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/bpf_helpers.h> 11 12 /* Max supported length of a string with unsigned long in base 10 (pow2 - 1). */ 13 #define MAX_ULONG_STR_LEN 0xF 14 15 /* Max supported length of sysctl value string (pow2). */ 16 #define MAX_VALUE_STR_LEN 0x40 17 18 #ifndef ARRAY_SIZE 19 #define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0])) 20 #endif 21 22 static __always_inline int is_tcp_mem(struct bpf_sysctl *ctx) 23 { 24 char tcp_mem_name[] = "net/ipv4/tcp_mem"; 25 unsigned char i; 26 char name[64]; 27 int ret; 28 29 memset(name, 0, sizeof(name)); 30 ret = bpf_sysctl_get_name(ctx, name, sizeof(name), 0); 31 if (ret < 0 || ret != sizeof(tcp_mem_name) - 1) 32 return 0; 33 34 #pragma clang loop unroll(full) 35 for (i = 0; i < sizeof(tcp_mem_name); ++i) 36 if (name[i] != tcp_mem_name[i]) 37 return 0; 38 39 return 1; 40 } 41 42 SEC("cgroup/sysctl") 43 int sysctl_tcp_mem(struct bpf_sysctl *ctx) 44 { 45 unsigned long tcp_mem[3] = {0, 0, 0}; 46 char value[MAX_VALUE_STR_LEN]; 47 unsigned char i, off = 0; 48 volatile int ret; 49 50 if (ctx->write) 51 return 0; 52 53 if (!is_tcp_mem(ctx)) 54 return 0; 55 56 ret = bpf_sysctl_get_current_value(ctx, value, MAX_VALUE_STR_LEN); 57 if (ret < 0 || ret >= MAX_VALUE_STR_LEN) 58 return 0; 59 60 #pragma clang loop unroll(full) 61 for (i = 0; i < ARRAY_SIZE(tcp_mem); ++i) { 62 ret = bpf_strtoul(value + off, MAX_ULONG_STR_LEN, 0, 63 tcp_mem + i); 64 if (ret <= 0 || ret > MAX_ULONG_STR_LEN) 65 return 0; 66 off += ret & MAX_ULONG_STR_LEN; 67 } 68 69 70 return tcp_mem[0] < tcp_mem[1] && tcp_mem[1] < tcp_mem[2]; 71 } 72 73 char _license[] SEC("license") = "GPL"; 74