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 #include "bpf_compiler.h" 13 14 /* Max supported length of a string with unsigned long in base 10 (pow2 - 1). */ 15 #define MAX_ULONG_STR_LEN 0xF 16 17 /* Max supported length of sysctl value string (pow2). */ 18 #define MAX_VALUE_STR_LEN 0x40 19 20 #ifndef ARRAY_SIZE 21 #define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0])) 22 #endif 23 24 const char tcp_mem_name[] = "net/ipv4/tcp_mem"; 25 static __always_inline int is_tcp_mem(struct bpf_sysctl *ctx) 26 { 27 unsigned char i; 28 char name[sizeof(tcp_mem_name)]; 29 int ret; 30 31 memset(name, 0, sizeof(name)); 32 ret = bpf_sysctl_get_name(ctx, name, sizeof(name), 0); 33 if (ret < 0 || ret != sizeof(tcp_mem_name) - 1) 34 return 0; 35 36 __pragma_loop_unroll_full 37 for (i = 0; i < sizeof(tcp_mem_name); ++i) 38 if (name[i] != tcp_mem_name[i]) 39 return 0; 40 41 return 1; 42 } 43 44 SEC("cgroup/sysctl") 45 int sysctl_tcp_mem(struct bpf_sysctl *ctx) 46 { 47 unsigned long tcp_mem[3] = {0, 0, 0}; 48 char value[MAX_VALUE_STR_LEN]; 49 unsigned char i, off = 0; 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_loop_unroll_full 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 72 return tcp_mem[0] < tcp_mem[1] && tcp_mem[1] < tcp_mem[2]; 73 } 74 75 char _license[] SEC("license") = "GPL"; 76