cred: Use KMEM_CACHE() instead of kmem_cache_create()

Commit 0a31bd5f2bbb ("KMEM_CACHE(): simplify slab cache creation")
introduces a new macro. Use the new KMEM_CACHE() macro instead of
direct kmem

cred: Use KMEM_CACHE() instead of kmem_cache_create()

Commit 0a31bd5f2bbb ("KMEM_CACHE(): simplify slab cache creation")
introduces a new macro. Use the new KMEM_CACHE() macro instead of
direct kmem_cache_create() to simplify the creation of SLAB caches.

Signed-off-by: Kunwu Chan <chentao@kylinos.cn>
[PM: alignment fixes in both code and description]
Signed-off-by: Paul Moore <paul@paul-moore.com>

show more ...

cred: get rid of CONFIG_DEBUG_CREDENTIALS

This code is rarely (never?) enabled by distros, and it hasn't caught
anything in decades. Let's kill off this legacy debug code.

Suggested-by: Linus Torva

cred: get rid of CONFIG_DEBUG_CREDENTIALS

This code is rarely (never?) enabled by distros, and it hasn't caught
anything in decades. Let's kill off this legacy debug code.

Suggested-by: Linus Torvalds <torvalds@linuxfoundation.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

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cred: switch to using atomic_long_t

There are multiple ways to grab references to credentials, and the only
protection we have against overflowing it is the memory required to do
so.

With memory si

cred: switch to using atomic_long_t

There are multiple ways to grab references to credentials, and the only
protection we have against overflowing it is the memory required to do
so.

With memory sizes only moving in one direction, let's bump the reference
count to 64-bit and move it outside the realm of feasibly overflowing.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

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groups: Convert group_info.usage to refcount_t

atomic_t variables are currently used to implement reference counters
with the following properties:
- counter is initialized to 1 using atomic_set()

groups: Convert group_info.usage to refcount_t

atomic_t variables are currently used to implement reference counters
with the following properties:
- counter is initialized to 1 using atomic_set()
- a resource is freed upon counter reaching zero
- once counter reaches zero, its further
increments aren't allowed
- counter schema uses basic atomic operations
(set, inc, inc_not_zero, dec_and_test, etc.)

Such atomic variables should be converted to a newly provided
refcount_t type and API that prevents accidental counter overflows and
underflows. This is important since overflows and underflows can lead
to use-after-free situation and be exploitable.

The variable group_info.usage is used as pure reference counter.
Convert it to refcount_t and fix up the operations.

**Important note for maintainers:

Some functions from refcount_t API defined in refcount.h have different
memory ordering guarantees than their atomic counterparts. Please check
Documentation/core-api/refcount-vs-atomic.rst for more information.

Normally the differences should not matter since refcount_t provides
enough guarantees to satisfy the refcounting use cases, but in some
rare cases it might matter. Please double check that you don't have
some undocumented memory guarantees for this variable usage.

For the group_info.usage it might make a difference in following places:
- put_group_info(): decrement in refcount_dec_and_test() only
provides RELEASE ordering and ACQUIRE ordering on success vs. fully
ordered atomic counterpart

Suggested-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Elena Reshetova <elena.reshetova@intel.com>
Reviewed-by: David Windsor <dwindsor@gmail.com>
Reviewed-by: Hans Liljestrand <ishkamiel@gmail.com>
Link: https://lore.kernel.org/r/20230818041456.gonna.009-kees@kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>

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cred: add get_cred_many and put_cred_many

Some of the frequent consumers of get_cred and put_cred operate on 2
references on the same creds back-to-back.

Switch them to doing the work in one go ins

cred: add get_cred_many and put_cred_many

Some of the frequent consumers of get_cred and put_cred operate on 2
references on the same creds back-to-back.

Switch them to doing the work in one go instead.

Signed-off-by: Mateusz Guzik <mjguzik@gmail.com>
[PM: removed changelog from commit description]
Signed-off-by: Paul Moore <paul@paul-moore.com>

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cred: convert printks to pr_<level>

Use current logging style.

Link: https://lkml.kernel.org/r/20230625033452.GA22858@didi-ThinkCentre-M930t-N000
Signed-off-by: tiozhang <tiozhang@didiglobal.com>
R

cred: convert printks to pr_<level>

Use current logging style.

Link: https://lkml.kernel.org/r/20230625033452.GA22858@didi-ThinkCentre-M930t-N000
Signed-off-by: tiozhang <tiozhang@didiglobal.com>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Joe Perches <joe@perches.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Luis Chamberlain <mcgrof@kernel.org>
Cc: Paulo Alcantara <pc@cjr.nz>
Cc: Weiping Zhang <zwp10758@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

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cred: Do not default to init_cred in prepare_kernel_cred()

A common exploit pattern for ROP attacks is to abuse prepare_kernel_cred()
in order to construct escalated privileges[1]. Instead of provid

cred: Do not default to init_cred in prepare_kernel_cred()

A common exploit pattern for ROP attacks is to abuse prepare_kernel_cred()
in order to construct escalated privileges[1]. Instead of providing a
short-hand argument (NULL) to the "daemon" argument to indicate using
init_cred as the base cred, require that "daemon" is always set to
an actual task. Replace all existing callers that were passing NULL
with &init_task.

Future attacks will need to have sufficiently powerful read/write
primitives to have found an appropriately privileged task and written it
to the ROP stack as an argument to succeed, which is similarly difficult
to the prior effort needed to escalate privileges before struct cred
existed: locate the current cred and overwrite the uid member.

This has the added benefit of meaning that prepare_kernel_cred() can no
longer exceed the privileges of the init task, which may have changed from
the original init_cred (e.g. dropping capabilities from the bounding set).

[1] https://google.com/search?q=commit_creds(prepare_kernel_cred(0))

Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: David Howells <dhowells@redhat.com>
Cc: "Rafael J. Wysocki" <rafael@kernel.org>
Cc: Steve French <sfrench@samba.org>
Cc: Ronnie Sahlberg <lsahlber@redhat.com>
Cc: Shyam Prasad N <sprasad@microsoft.com>
Cc: Tom Talpey <tom@talpey.com>
Cc: Namjae Jeon <linkinjeon@kernel.org>
Cc: Trond Myklebust <trond.myklebust@hammerspace.com>
Cc: Anna Schumaker <anna@kernel.org>
Cc: Chuck Lever <chuck.lever@oracle.com>
Cc: Jeff Layton <jlayton@kernel.org>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: Paolo Abeni <pabeni@redhat.com>
Cc: "Michal Koutný" <mkoutny@suse.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: linux-cifs@vger.kernel.org
Cc: samba-technical@lists.samba.org
Cc: linux-nfs@vger.kernel.org
Cc: netdev@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
Acked-by: Luis Chamberlain <mcgrof@kernel.org>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Acked-by: Russ Weight <russell.h.weight@intel.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Paulo Alcantara (SUSE) <pc@cjr.nz>
Link: https://lore.kernel.org/r/20221026232943.never.775-kees@kernel.org

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x86: Mark __invalid_creds() __noreturn

vmlinux.o: warning: objtool: ksys_unshare()+0x36c: unreachable instruction

0000 0000000000067040 <ksys_unshare>:
...
0364 673a4: 4c 89 ef mov

x86: Mark __invalid_creds() __noreturn

vmlinux.o: warning: objtool: ksys_unshare()+0x36c: unreachable instruction

0000 0000000000067040 <ksys_unshare>:
...
0364 673a4: 4c 89 ef mov %r13,%rdi
0367 673a7: e8 00 00 00 00 call 673ac <ksys_unshare+0x36c> 673a8: R_X86_64_PLT32 __invalid_creds-0x4
036c 673ac: e9 28 ff ff ff jmp 672d9 <ksys_unshare+0x299>
0371 673b1: 41 bc f4 ff ff ff mov $0xfffffff4,%r12d
0377 673b7: e9 80 fd ff ff jmp 6713c <ksys_unshare+0xfc>

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/Yi9gOW9f1GGwwUD6@hirez.programming.kicks-ass.net

show more ...

ucounts: Base set_cred_ucounts changes on the real user

Michal Koutný <mkoutny@suse.com> wrote:
> Tasks are associated to multiple users at once. Historically and as per
> setrlimit(2) RLIMIT_NPROC

ucounts: Base set_cred_ucounts changes on the real user

Michal Koutný <mkoutny@suse.com> wrote:
> Tasks are associated to multiple users at once. Historically and as per
> setrlimit(2) RLIMIT_NPROC is enforce based on real user ID.
>
> The commit 21d1c5e386bc ("Reimplement RLIMIT_NPROC on top of ucounts")
> made the accounting structure "indexed" by euid and hence potentially
> account tasks differently.
>
> The effective user ID may be different e.g. for setuid programs but
> those are exec'd into already existing task (i.e. below limit), so
> different accounting is moot.
>
> Some special setresuid(2) users may notice the difference, justifying
> this fix.

I looked at cred->ucount and it is only used for rlimit operations
that were previously stored in cred->user. Making the fact
cred->ucount can refer to a different user from cred->user a bug,
affecting all uses of cred->ulimit not just RLIMIT_NPROC.

Fix set_cred_ucounts to always use the real uid not the effective uid.

Further simplify set_cred_ucounts by noticing that set_cred_ucounts
somehow retained a draft version of the check to see if alloc_ucounts
was needed that checks the new->user and new->user_ns against the
current_real_cred(). Remove that draft version of the check.

All that matters for setting the cred->ucounts are the user_ns and uid
fields in the cred.

Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/20220207121800.5079-4-mkoutny@suse.com
Link: https://lkml.kernel.org/r/20220216155832.680775-3-ebiederm@xmission.com
Reported-by: Michal Koutný <mkoutny@suse.com>
Reviewed-by: Michal Koutný <mkoutny@suse.com>
Fixes: 21d1c5e386bc ("Reimplement RLIMIT_NPROC on top of ucounts")
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

show more ...

ucounts: In set_cred_ucounts assume new->ucounts is non-NULL

Any cred that is destined for use by commit_creds must have a non-NULL
cred->ucounts field. Only curing credential construction is a NUL

ucounts: In set_cred_ucounts assume new->ucounts is non-NULL

Any cred that is destined for use by commit_creds must have a non-NULL
cred->ucounts field. Only curing credential construction is a NULL
cred->ucounts valid. Only abort_creds, put_cred, and put_cred_rcu
needs to deal with a cred with a NULL ucount. As set_cred_ucounts is
non of those case don't confuse people by handling something that can
not happen.

Link: https://lkml.kernel.org/r/871r4irzds.fsf_-_@disp2133
Tested-by: Yu Zhao <yuzhao@google.com>
Reviewed-by: Alexey Gladkov <legion@kernel.org>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

show more ...

ucounts: Move get_ucounts from cred_alloc_blank to key_change_session_keyring

Setting cred->ucounts in cred_alloc_blank does not make sense. The
uid and user_ns are deliberately not set in cred_all

ucounts: Move get_ucounts from cred_alloc_blank to key_change_session_keyring

Setting cred->ucounts in cred_alloc_blank does not make sense. The
uid and user_ns are deliberately not set in cred_alloc_blank but
instead the setting is delayed until key_change_session_keyring.

So move dealing with ucounts into key_change_session_keyring as well.

Unfortunately that movement of get_ucounts adds a new failure mode to
key_change_session_keyring. I do not see anything stopping the parent
process from calling setuid and changing the relevant part of it's
cred while keyctl_session_to_parent is running making it fundamentally
necessary to call get_ucounts in key_change_session_keyring. Which
means that the new failure mode cannot be avoided.

A failure of key_change_session_keyring results in a single threaded
parent keeping it's existing credentials. Which results in the parent
process not being able to access the session keyring and whichever
keys are in the new keyring.

Further get_ucounts is only expected to fail if the number of bits in
the refernece count for the structure is too few.

Since the code has no other way to report the failure of get_ucounts
and because such failures are not expected to be common add a WARN_ONCE
to report this problem to userspace.

Between the WARN_ONCE and the parent process not having access to
the keys in the new session keyring I expect any failure of get_ucounts
will be noticed and reported and we can find another way to handle this
condition. (Possibly by just making ucounts->count an atomic_long_t).

Cc: stable@vger.kernel.org
Fixes: 905ae01c4ae2 ("Add a reference to ucounts for each cred")
Link: https://lkml.kernel.org/r/7k0ias0uf.fsf_-_@disp2133
Tested-by: Yu Zhao <yuzhao@google.com>
Reviewed-by: Alexey Gladkov <legion@kernel.org>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

show more ...

ucounts: Proper error handling in set_cred_ucounts

Instead of leaking the ucounts in new if alloc_ucounts fails, store
the result of alloc_ucounts into a temporary variable, which is later
assigned

ucounts: Proper error handling in set_cred_ucounts

Instead of leaking the ucounts in new if alloc_ucounts fails, store
the result of alloc_ucounts into a temporary variable, which is later
assigned to new->ucounts.

Cc: stable@vger.kernel.org
Fixes: 905ae01c4ae2 ("Add a reference to ucounts for each cred")
Link: https://lkml.kernel.org/r/87pms2s0v8.fsf_-_@disp2133
Tested-by: Yu Zhao <yuzhao@google.com>
Reviewed-by: Alexey Gladkov <legion@kernel.org>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

show more ...

ucounts: Pair inc_rlimit_ucounts with dec_rlimit_ucoutns in commit_creds

The purpose of inc_rlimit_ucounts and dec_rlimit_ucounts in commit_creds
is to change which rlimit counter is used to track a

ucounts: Pair inc_rlimit_ucounts with dec_rlimit_ucoutns in commit_creds

The purpose of inc_rlimit_ucounts and dec_rlimit_ucounts in commit_creds
is to change which rlimit counter is used to track a process when the
credentials changes.

Use the same test for both to guarantee the tracking is correct.

Cc: stable@vger.kernel.org
Fixes: 21d1c5e386bc ("Reimplement RLIMIT_NPROC on top of ucounts")
Link: https://lkml.kernel.org/r/87v91us0w4.fsf_-_@disp2133
Tested-by: Yu Zhao <yuzhao@google.com>
Reviewed-by: Alexey Gladkov <legion@kernel.org>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

show more ...

ucounts: Increase ucounts reference counter before the security hook

We need to increment the ucounts reference counter befor security_prepare_creds()
because this function may fail and abort_creds(

ucounts: Increase ucounts reference counter before the security hook

We need to increment the ucounts reference counter befor security_prepare_creds()
because this function may fail and abort_creds() will try to decrement
this reference.

[ 96.465056][ T8641] FAULT_INJECTION: forcing a failure.
[ 96.465056][ T8641] name fail_page_alloc, interval 1, probability 0, space 0, times 0
[ 96.478453][ T8641] CPU: 1 PID: 8641 Comm: syz-executor668 Not tainted 5.14.0-rc6-syzkaller #0
[ 96.487215][ T8641] Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
[ 96.497254][ T8641] Call Trace:
[ 96.500517][ T8641] dump_stack_lvl+0x1d3/0x29f
[ 96.505758][ T8641] ? show_regs_print_info+0x12/0x12
[ 96.510944][ T8641] ? log_buf_vmcoreinfo_setup+0x498/0x498
[ 96.516652][ T8641] should_fail+0x384/0x4b0
[ 96.521141][ T8641] prepare_alloc_pages+0x1d1/0x5a0
[ 96.526236][ T8641] __alloc_pages+0x14d/0x5f0
[ 96.530808][ T8641] ? __rmqueue_pcplist+0x2030/0x2030
[ 96.536073][ T8641] ? lockdep_hardirqs_on_prepare+0x3e2/0x750
[ 96.542056][ T8641] ? alloc_pages+0x3f3/0x500
[ 96.546635][ T8641] allocate_slab+0xf1/0x540
[ 96.551120][ T8641] ___slab_alloc+0x1cf/0x350
[ 96.555689][ T8641] ? kzalloc+0x1d/0x30
[ 96.559740][ T8641] __kmalloc+0x2e7/0x390
[ 96.563980][ T8641] ? kzalloc+0x1d/0x30
[ 96.568029][ T8641] kzalloc+0x1d/0x30
[ 96.571903][ T8641] security_prepare_creds+0x46/0x220
[ 96.577174][ T8641] prepare_creds+0x411/0x640
[ 96.581747][ T8641] __sys_setfsuid+0xe2/0x3a0
[ 96.586333][ T8641] do_syscall_64+0x3d/0xb0
[ 96.590739][ T8641] entry_SYSCALL_64_after_hwframe+0x44/0xae
[ 96.596611][ T8641] RIP: 0033:0x445a69
[ 96.600483][ T8641] Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 11 15 00 00 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48
[ 96.620152][ T8641] RSP: 002b:00007f1054173318 EFLAGS: 00000246 ORIG_RAX: 000000000000007a
[ 96.628543][ T8641] RAX: ffffffffffffffda RBX: 00000000004ca4c8 RCX: 0000000000445a69
[ 96.636600][ T8641] RDX: 0000000000000010 RSI: 00007f10541732f0 RDI: 0000000000000000
[ 96.644550][ T8641] RBP: 00000000004ca4c0 R08: 0000000000000001 R09: 0000000000000000
[ 96.652500][ T8641] R10: 0000000000000000 R11: 0000000000000246 R12: 00000000004ca4cc
[ 96.660631][ T8641] R13: 00007fffffe0b62f R14: 00007f1054173400 R15: 0000000000022000

Fixes: 905ae01c4ae2 ("Add a reference to ucounts for each cred")
Reported-by: syzbot+01985d7909f9468f013c@syzkaller.appspotmail.com
Signed-off-by: Alexey Gladkov <legion@kernel.org>
Link: https://lkml.kernel.org/r/97433b1742c3331f02ad92de5a4f07d673c90613.1629735352.git.legion@kernel.org
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>

show more ...

cred: add missing return error code when set_cred_ucounts() failed

If set_cred_ucounts() failed, we need return the error code.

Fixes: 905ae01c4ae2 ("Add a reference to ucounts for each cred")
Repo

cred: add missing return error code when set_cred_ucounts() failed

If set_cred_ucounts() failed, we need return the error code.

Fixes: 905ae01c4ae2 ("Add a reference to ucounts for each cred")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Link: https://lkml.kernel.org/r/20210526143805.2549649-1-yangyingliang@huawei.com
Reviewed-by: Alexey Gladkov <legion@kernel.org>
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>

show more ...

kernel/cred.c: make init_groups static

init_groups is declared in both cred.h and init_task.h, but it is not
actually referenced anywhere outside of cred.c where it is defined. So
make it static an

kernel/cred.c: make init_groups static

init_groups is declared in both cred.h and init_task.h, but it is not
actually referenced anywhere outside of cred.c where it is defined. So
make it static and remove the declarations.

Link: https://lkml.kernel.org/r/20210310220102.2484201-1-linux@rasmusvillemoes.dk
Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

show more ...

Reimplement RLIMIT_NPROC on top of ucounts

The rlimit counter is tied to uid in the user_namespace. This allows
rlimit values to be specified in userns even if they are already
globally exceeded by

Reimplement RLIMIT_NPROC on top of ucounts

The rlimit counter is tied to uid in the user_namespace. This allows
rlimit values to be specified in userns even if they are already
globally exceeded by the user. However, the value of the previous
user_namespaces cannot be exceeded.

To illustrate the impact of rlimits, let's say there is a program that
does not fork. Some service-A wants to run this program as user X in
multiple containers. Since the program never fork the service wants to
set RLIMIT_NPROC=1.

service-A
\- program (uid=1000, container1, rlimit_nproc=1)
\- program (uid=1000, container2, rlimit_nproc=1)

The service-A sets RLIMIT_NPROC=1 and runs the program in container1.
When the service-A tries to run a program with RLIMIT_NPROC=1 in
container2 it fails since user X already has one running process.

We cannot use existing inc_ucounts / dec_ucounts because they do not
allow us to exceed the maximum for the counter. Some rlimits can be
overlimited by root or if the user has the appropriate capability.

Changelog

v11:
* Change inc_rlimit_ucounts() which now returns top value of ucounts.
* Drop inc_rlimit_ucounts_and_test() because the return code of
inc_rlimit_ucounts() can be checked.

Signed-off-by: Alexey Gladkov <legion@kernel.org>
Link: https://lkml.kernel.org/r/c5286a8aa16d2d698c222f7532f3d735c82bc6bc.1619094428.git.legion@kernel.org
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>

show more ...

Add a reference to ucounts for each cred

For RLIMIT_NPROC and some other rlimits the user_struct that holds the
global limit is kept alive for the lifetime of a process by keeping it
in struct cred.

Add a reference to ucounts for each cred

For RLIMIT_NPROC and some other rlimits the user_struct that holds the
global limit is kept alive for the lifetime of a process by keeping it
in struct cred. Adding a pointer to ucounts in the struct cred will
allow to track RLIMIT_NPROC not only for user in the system, but for
user in the user_namespace.

Updating ucounts may require memory allocation which may fail. So, we
cannot change cred.ucounts in the commit_creds() because this function
cannot fail and it should always return 0. For this reason, we modify
cred.ucounts before calling the commit_creds().

Changelog

v6:
* Fix null-ptr-deref in is_ucounts_overlimit() detected by trinity. This
error was caused by the fact that cred_alloc_blank() left the ucounts
pointer empty.

Reported-by: kernel test robot <oliver.sang@intel.com>
Signed-off-by: Alexey Gladkov <legion@kernel.org>
Link: https://lkml.kernel.org/r/b37aaef28d8b9b0d757e07ba6dd27281bbe39259.1619094428.git.legion@kernel.org
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>

show more ...

exec: Teach prepare_exec_creds how exec treats uids & gids

It is almost possible to use the result of prepare_exec_creds with no
modifications during exec. Update prepare_exec_creds to initialize
t

exec: Teach prepare_exec_creds how exec treats uids & gids

It is almost possible to use the result of prepare_exec_creds with no
modifications during exec. Update prepare_exec_creds to initialize
the suid and the fsuid to the euid, and the sgid and the fsgid to the
egid. This is all that is needed to handle the common case of exec
when nothing special like a setuid exec is happening.

That this preserves the existing behavior of exec can be verified
by examing bprm_fill_uid and cap_bprm_set_creds.

This change makes it clear that the later parts of exec that
update bprm->cred are just need to handle special cases such
as setuid exec and change of domains.

Link: https://lkml.kernel.org/r/871rng22dm.fsf_-_@x220.int.ebiederm.org
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

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kernel: doc: remove outdated comment cred.c

This removes an outdated comment in prepare_kernel_cred.

There is no "cred_replace_mutex" any more, so the comment must
go away.

Signed-off-by: Bernd Ed

kernel: doc: remove outdated comment cred.c

This removes an outdated comment in prepare_kernel_cred.

There is no "cred_replace_mutex" any more, so the comment must
go away.

Signed-off-by: Bernd Edlinger <bernd.edlinger@hotmail.de>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>

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keys: Fix request_key() cache

When the key cached by request_key() and co. is cleaned up on exit(),
the code looks in the wrong task_struct, and so clears the wrong cache.
This leads to anomalies i

keys: Fix request_key() cache

When the key cached by request_key() and co. is cleaned up on exit(),
the code looks in the wrong task_struct, and so clears the wrong cache.
This leads to anomalies in key refcounting when doing, say, a kernel
build on an afs volume, that then trigger kasan to report a
use-after-free when the key is viewed in /proc/keys.

Fix this by making exit_creds() look in the passed-in task_struct rather
than in current (the task_struct cleanup code is deferred by RCU and
potentially run in another task).

Fixes: 7743c48e54ee ("keys: Cache result of request_key*() temporarily in task_struct")
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

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memcg: account security cred as well to kmemcg

The cred_jar kmem_cache is already memcg accounted in the current kernel
but cred->security is not. Account cred->security to kmemcg.

Recently we saw

memcg: account security cred as well to kmemcg

The cred_jar kmem_cache is already memcg accounted in the current kernel
but cred->security is not. Account cred->security to kmemcg.

Recently we saw high root slab usage on our production and on further
inspection, we found a buggy application leaking processes. Though that
buggy application was contained within its memcg but we observe much
more system memory overhead, couple of GiBs, during that period. This
overhead can adversely impact the isolation on the system.

One source of high overhead we found was cred->security objects, which
have a lifetime of at least the life of the process which allocated
them.

Link: http://lkml.kernel.org/r/20191205223721.40034-1-shakeelb@google.com
Signed-off-by: Shakeel Butt <shakeelb@google.com>
Acked-by: Chris Down <chris@chrisdown.name>
Reviewed-by: Roman Gushchin <guro@fb.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

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access: avoid the RCU grace period for the temporary subjective credentials

It turns out that 'access()' (and 'faccessat()') can cause a lot of RCU
work because it installs a temporary credential th

access: avoid the RCU grace period for the temporary subjective credentials

It turns out that 'access()' (and 'faccessat()') can cause a lot of RCU
work because it installs a temporary credential that gets allocated and
freed for each system call.

The allocation and freeing overhead is mostly benign, but because
credentials can be accessed under the RCU read lock, the freeing
involves a RCU grace period.

Which is not a huge deal normally, but if you have a lot of access()
calls, this causes a fair amount of seconday damage: instead of having a
nice alloc/free patterns that hits in hot per-CPU slab caches, you have
all those delayed free's, and on big machines with hundreds of cores,
the RCU overhead can end up being enormous.

But it turns out that all of this is entirely unnecessary. Exactly
because access() only installs the credential as the thread-local
subjective credential, the temporary cred pointer doesn't actually need
to be RCU free'd at all. Once we're done using it, we can just free it
synchronously and avoid all the RCU overhead.

So add a 'non_rcu' flag to 'struct cred', which can be set by users that
know they only use it in non-RCU context (there are other potential
users for this). We can make it a union with the rcu freeing list head
that we need for the RCU case, so this doesn't need any extra storage.

Note that this also makes 'get_current_cred()' clear the new non_rcu
flag, in case we have filesystems that take a long-term reference to the
cred and then expect the RCU delayed freeing afterwards. It's not
entirely clear that this is required, but it makes for clear semantics:
the subjective cred remains non-RCU as long as you only access it
synchronously using the thread-local accessors, but you _can_ use it as
a generic cred if you want to.

It is possible that we should just remove the whole RCU markings for
->cred entirely. Only ->real_cred is really supposed to be accessed
through RCU, and the long-term cred copies that nfs uses might want to
explicitly re-enable RCU freeing if required, rather than have
get_current_cred() do it implicitly.

But this is a "minimal semantic changes" change for the immediate
problem.

Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Eric Dumazet <edumazet@google.com>
Acked-by: Paul E. McKenney <paulmck@linux.ibm.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Jan Glauber <jglauber@marvell.com>
Cc: Jiri Kosina <jikos@kernel.org>
Cc: Jayachandran Chandrasekharan Nair <jnair@marvell.com>
Cc: Greg KH <greg@kroah.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: David Howells <dhowells@redhat.com>
Cc: Miklos Szeredi <miklos@szeredi.hu>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

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keys: Cache result of request_key*() temporarily in task_struct

If a filesystem uses keys to hold authentication tokens, then it needs a
token for each VFS operation that might perform an authentica

keys: Cache result of request_key*() temporarily in task_struct

If a filesystem uses keys to hold authentication tokens, then it needs a
token for each VFS operation that might perform an authentication check -
either by passing it to the server, or using to perform a check based on
authentication data cached locally.

For open files this isn't a problem, since the key should be cached in the
file struct since it represents the subject performing operations on that
file descriptor.

During pathwalk, however, there isn't anywhere to cache the key, except
perhaps in the nameidata struct - but that isn't exposed to the
filesystems. Further, a pathwalk can incur a lot of operations, calling
one or more of the following, for instance:

->lookup()
->permission()
->d_revalidate()
->d_automount()
->get_acl()
->getxattr()

on each dentry/inode it encounters - and each one may need to call
request_key(). And then, at the end of pathwalk, it will call the actual
operation:

->mkdir()
->mknod()
->getattr()
->open()
...

which may need to go and get the token again.

However, it is very likely that all of the operations on a single
dentry/inode - and quite possibly a sequence of them - will all want to use
the same authentication token, which suggests that caching it would be a
good idea.

To this end:

(1) Make it so that a positive result of request_key() and co. that didn't
require upcalling to userspace is cached temporarily in task_struct.

(2) The cache is 1 deep, so a new result displaces the old one.

(3) The key is released by exit and by notify-resume.

(4) The cache is cleared in a newly forked process.

Signed-off-by: David Howells <dhowells@redhat.com>

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ptrace: restore smp_rmb() in __ptrace_may_access()

Restore the read memory barrier in __ptrace_may_access() that was deleted
a couple years ago. Also add comments on this barrier and the one it pair

ptrace: restore smp_rmb() in __ptrace_may_access()

Restore the read memory barrier in __ptrace_may_access() that was deleted
a couple years ago. Also add comments on this barrier and the one it pairs
with to explain why they're there (as far as I understand).

Fixes: bfedb589252c ("mm: Add a user_ns owner to mm_struct and fix ptrace permission checks")
Cc: stable@vger.kernel.org
Acked-by: Kees Cook <keescook@chromium.org>
Acked-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Jann Horn <jannh@google.com>
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>

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