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 #include "bpf_misc.h" 14 15 /* Max supported length of a string with unsigned long in base 10 (pow2 - 1). */ 16 #define MAX_ULONG_STR_LEN 0xF 17 18 /* Max supported length of sysctl value string (pow2). */ 19 #define MAX_VALUE_STR_LEN 0x40 20 21 const char tcp_mem_name[] = "net/ipv4/tcp_mem"; 22 static __always_inline int is_tcp_mem(struct bpf_sysctl *ctx) 23 { 24 unsigned char i; 25 char name[sizeof(tcp_mem_name)]; 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_loop_unroll_full 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[3] = {0, 0, 0}; 45 char value[MAX_VALUE_STR_LEN]; 46 unsigned char i, off = 0; 47 volatile int ret; 48 49 if (ctx->write) 50 return 0; 51 52 if (!is_tcp_mem(ctx)) 53 return 0; 54 55 ret = bpf_sysctl_get_current_value(ctx, value, MAX_VALUE_STR_LEN); 56 if (ret < 0 || ret >= MAX_VALUE_STR_LEN) 57 return 0; 58 59 __pragma_loop_unroll_full 60 for (i = 0; i < ARRAY_SIZE(tcp_mem); ++i) { 61 ret = bpf_strtoul(value + off, MAX_ULONG_STR_LEN, 0, 62 tcp_mem + i); 63 if (ret <= 0 || ret > MAX_ULONG_STR_LEN) 64 return 0; 65 off += ret & MAX_ULONG_STR_LEN; 66 } 67 68 69 return tcp_mem[0] < tcp_mem[1] && tcp_mem[1] < tcp_mem[2]; 70 } 71 72 char _license[] SEC("license") = "GPL"; 73