1 /* Create /proc/self/fd-related names for subfiles of open directories. 2 3 Copyright (C) 2006, 2009-2012 Free Software Foundation, Inc. 4 5 This program is free software: you can redistribute it and/or modify 6 it under the terms of the GNU General Public License as published by 7 the Free Software Foundation; either version 3 of the License, or 8 (at your option) any later version. 9 10 This program is distributed in the hope that it will be useful, 11 but WITHOUT ANY WARRANTY; without even the implied warranty of 12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 13 GNU General Public License for more details. 14 15 You should have received a copy of the GNU General Public License 16 along with this program. If not, see <http://www.gnu.org/licenses/>. */ 17 18 /* Written by Paul Eggert. */ 19 20 #include <config.h> 21 22 #include "openat-priv.h" 23 24 #include <sys/types.h> 25 #include <sys/stat.h> 26 #include <fcntl.h> 27 28 #include <stdio.h> 29 #include <stdlib.h> 30 #include <string.h> 31 #include <unistd.h> 32 33 #include "intprops.h" 34 35 /* The results of open() in this file are not used with fchdir, 36 and we do not leak fds to any single-threaded code that could use stdio, 37 therefore save some unnecessary work in fchdir.c. 38 FIXME - if the kernel ever adds support for multi-thread safety for 39 avoiding standard fds, then we should use open_safer. */ 40 #undef open 41 #undef close 42 43 #define PROC_SELF_FD_FORMAT "/proc/self/fd/%d/%s" 44 45 #define PROC_SELF_FD_NAME_SIZE_BOUND(len) \ 46 (sizeof PROC_SELF_FD_FORMAT - sizeof "%d%s" \ 47 + INT_STRLEN_BOUND (int) + (len) + 1) 48 49 50 /* Set BUF to the expansion of PROC_SELF_FD_FORMAT, using FD and FILE 51 respectively for %d and %s. If successful, return BUF if the 52 result fits in BUF, dynamically allocated memory otherwise. But 53 return NULL if /proc is not reliable, either because the operating 54 system support is lacking or because memory is low. */ 55 char * 56 openat_proc_name (char buf[OPENAT_BUFFER_SIZE], int fd, char const *file) 57 { 58 static int proc_status = 0; 59 60 /* Make sure the caller gets ENOENT when appropriate. */ 61 if (!*file) 62 { 63 buf[0] = '\0'; 64 return buf; 65 } 66 67 if (! proc_status) 68 { 69 /* Set PROC_STATUS to a positive value if /proc/self/fd is 70 reliable, and a negative value otherwise. Solaris 10 71 /proc/self/fd mishandles "..", and any file name might expand 72 to ".." after symbolic link expansion, so avoid /proc/self/fd 73 if it mishandles "..". Solaris 10 has openat, but this 74 problem is exhibited on code that built on Solaris 8 and 75 running on Solaris 10. */ 76 77 int proc_self_fd = open ("/proc/self/fd", 78 O_SEARCH | O_DIRECTORY | O_NOCTTY | O_NONBLOCK); 79 if (proc_self_fd < 0) 80 proc_status = -1; 81 else 82 { 83 /* Detect whether /proc/self/fd/%i/../fd exists, where %i is the 84 number of a file descriptor open on /proc/self/fd. On Linux, 85 that name resolves to /proc/self/fd, which was opened above. 86 However, on Solaris, it may resolve to /proc/self/fd/fd, which 87 cannot exist, since all names in /proc/self/fd are numeric. */ 88 char dotdot_buf[PROC_SELF_FD_NAME_SIZE_BOUND (sizeof "../fd" - 1)]; 89 sprintf (dotdot_buf, PROC_SELF_FD_FORMAT, proc_self_fd, "../fd"); 90 proc_status = access (dotdot_buf, F_OK) ? -1 : 1; 91 close (proc_self_fd); 92 } 93 } 94 95 if (proc_status < 0) 96 return NULL; 97 else 98 { 99 size_t bufsize = PROC_SELF_FD_NAME_SIZE_BOUND (strlen (file)); 100 char *result = buf; 101 if (OPENAT_BUFFER_SIZE < bufsize) 102 { 103 result = malloc (bufsize); 104 if (! result) 105 return NULL; 106 } 107 sprintf (result, PROC_SELF_FD_FORMAT, fd, file); 108 return result; 109 } 110 } 111