1 // SPDX-License-Identifier: GPL-2.0 2 // Copyright (c) 2019 Facebook 3 4 #include <stdint.h> 5 #include <string.h> 6 7 #include <linux/stddef.h> 8 #include <linux/bpf.h> 9 10 #include "bpf_helpers.h" 11 12 #ifndef ARRAY_SIZE 13 #define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0])) 14 #endif 15 16 /* tcp_mem sysctl has only 3 ints, but this test is doing TCP_MEM_LOOPS */ 17 #define TCP_MEM_LOOPS 28 /* because 30 doesn't fit into 512 bytes of stack */ 18 #define MAX_ULONG_STR_LEN 7 19 #define MAX_VALUE_STR_LEN (TCP_MEM_LOOPS * MAX_ULONG_STR_LEN) 20 21 static __always_inline int is_tcp_mem(struct bpf_sysctl *ctx) 22 { 23 volatile char tcp_mem_name[] = "net/ipv4/tcp_mem/very_very_very_very_long_pointless_string"; 24 unsigned char i; 25 char name[64]; 26 int ret; 27 28 memset(name, 0, sizeof(name)); 29 ret = bpf_sysctl_get_name(ctx, name, sizeof(name), 0); 30 if (ret < 0 || ret != sizeof(tcp_mem_name) - 1) 31 return 0; 32 33 #pragma clang loop unroll(disable) 34 for (i = 0; i < sizeof(tcp_mem_name); ++i) 35 if (name[i] != tcp_mem_name[i]) 36 return 0; 37 38 return 1; 39 } 40 41 SEC("cgroup/sysctl") 42 int sysctl_tcp_mem(struct bpf_sysctl *ctx) 43 { 44 unsigned long tcp_mem[TCP_MEM_LOOPS] = {}; 45 char value[MAX_VALUE_STR_LEN]; 46 unsigned char i, off = 0; 47 /* a workaround to prevent compiler from generating 48 * codes verifier cannot handle yet. 49 */ 50 volatile int ret; 51 52 if (ctx->write) 53 return 0; 54 55 if (!is_tcp_mem(ctx)) 56 return 0; 57 58 ret = bpf_sysctl_get_current_value(ctx, value, MAX_VALUE_STR_LEN); 59 if (ret < 0 || ret >= MAX_VALUE_STR_LEN) 60 return 0; 61 62 #pragma clang loop unroll(disable) 63 for (i = 0; i < ARRAY_SIZE(tcp_mem); ++i) { 64 ret = bpf_strtoul(value + off, MAX_ULONG_STR_LEN, 0, 65 tcp_mem + i); 66 if (ret <= 0 || ret > MAX_ULONG_STR_LEN) 67 return 0; 68 off += ret & MAX_ULONG_STR_LEN; 69 } 70 71 return tcp_mem[0] < tcp_mem[1] && tcp_mem[1] < tcp_mem[2]; 72 } 73 74 char _license[] SEC("license") = "GPL"; 75