[PATCH net-next] sk-filter: Add ability to get socket filter program
From: Pavel Emelyanov <hidden>
Date: 2012-10-26 17:15:41
The SO_ATTACH_FILTER option is set only. I propose to add the get ability by using SO_ATTACH_FILTER in getsockopt. To be less irritating to eyes the SO_GET_FILTER alias to it is declared. There are two issues with getting filter back. First, kernel modifies the sock_filter->code on filter load, thus in order to return the filter element back to user we have to decode it into user-visible constants. Fortunately the modification in question is interconvertible. Second, the BPF_S_ALU_DIV_K code modifies the command argument k to speed up the run-time division by doing kernel_k = reciprocal(user_k). Bad news is that different user_k may result in same kernel_k, so we can't get the original user_k back. Good news is that we don't have to do it. What we need to is calculate a user2_k so, that reciprocal(user2_k) == reciprocal(user_k) == kernel_k i.e. if it's re-loaded back the compiled again value will be exactly the same as it was. That said, the user2_k can be calculated like this user2_k = reciprocal(kernel_k) with an exception, that if kernel_k == 0, then user2_k == 1. The optlen argument is treated like this -- when zero, kernel returns the amount of sock_fprog elements in filter, otherwise it should be large enough for the sock_fprog array. Signed-off-by: Pavel Emelyanov <redacted> ---
diff --git a/include/linux/filter.h b/include/linux/filter.h
index 24d251f..6ca0085 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h@@ -45,6 +45,7 @@ extern void sk_unattached_filter_destroy(struct sk_filter *fp); extern int sk_attach_filter(struct sock_fprog *fprog, struct sock *sk); extern int sk_detach_filter(struct sock *sk); extern int sk_chk_filter(struct sock_filter *filter, unsigned int flen); +extern int sk_get_filter(struct sock *sk, struct sock_filter __user *filter, unsigned len); #ifdef CONFIG_BPF_JIT extern void bpf_jit_compile(struct sk_filter *fp);
diff --git a/include/uapi/asm-generic/socket.h b/include/uapi/asm-generic/socket.h
index b1bea03..2d32d07 100644
--- a/include/uapi/asm-generic/socket.h
+++ b/include/uapi/asm-generic/socket.h@@ -43,6 +43,7 @@ /* Socket filtering */ #define SO_ATTACH_FILTER 26 #define SO_DETACH_FILTER 27 +#define SO_GET_FILTER SO_ATTACH_FILTER #define SO_PEERNAME 28 #define SO_TIMESTAMP 29
diff --git a/net/core/filter.c b/net/core/filter.c
index 3d92ebb..0a8cb99 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c@@ -751,3 +751,131 @@ int sk_detach_filter(struct sock *sk) return ret; } EXPORT_SYMBOL_GPL(sk_detach_filter); + +static void sk_decode_filter(struct sock_filter *filt, struct sock_filter *to) +{ + static const u16 decodes[] = { + [BPF_S_ALU_ADD_K] = BPF_ALU|BPF_ADD|BPF_K, + [BPF_S_ALU_ADD_X] = BPF_ALU|BPF_ADD|BPF_X, + [BPF_S_ALU_SUB_K] = BPF_ALU|BPF_SUB|BPF_K, + [BPF_S_ALU_SUB_X] = BPF_ALU|BPF_SUB|BPF_X, + [BPF_S_ALU_MUL_K] = BPF_ALU|BPF_MUL|BPF_K, + [BPF_S_ALU_MUL_X] = BPF_ALU|BPF_MUL|BPF_X, + [BPF_S_ALU_DIV_X] = BPF_ALU|BPF_DIV|BPF_X, + [BPF_S_ALU_MOD_K] = BPF_ALU|BPF_MOD|BPF_K, + [BPF_S_ALU_MOD_X] = BPF_ALU|BPF_MOD|BPF_X, + [BPF_S_ALU_AND_K] = BPF_ALU|BPF_AND|BPF_K, + [BPF_S_ALU_AND_X] = BPF_ALU|BPF_AND|BPF_X, + [BPF_S_ALU_OR_K] = BPF_ALU|BPF_OR|BPF_K, + [BPF_S_ALU_OR_X] = BPF_ALU|BPF_OR|BPF_X, + [BPF_S_ALU_XOR_K] = BPF_ALU|BPF_XOR|BPF_K, + [BPF_S_ALU_XOR_X] = BPF_ALU|BPF_XOR|BPF_X, + [BPF_S_ALU_LSH_K] = BPF_ALU|BPF_LSH|BPF_K, + [BPF_S_ALU_LSH_X] = BPF_ALU|BPF_LSH|BPF_X, + [BPF_S_ALU_RSH_K] = BPF_ALU|BPF_RSH|BPF_K, + [BPF_S_ALU_RSH_X] = BPF_ALU|BPF_RSH|BPF_X, + [BPF_S_ALU_NEG] = BPF_ALU|BPF_NEG, + [BPF_S_LD_W_ABS] = BPF_LD|BPF_W|BPF_ABS, + [BPF_S_LD_H_ABS] = BPF_LD|BPF_H|BPF_ABS, + [BPF_S_LD_B_ABS] = BPF_LD|BPF_B|BPF_ABS, + [BPF_S_ANC_PROTOCOL] = BPF_LD|BPF_B|BPF_ABS, + [BPF_S_ANC_PKTTYPE] = BPF_LD|BPF_B|BPF_ABS, + [BPF_S_ANC_IFINDEX] = BPF_LD|BPF_B|BPF_ABS, + [BPF_S_ANC_NLATTR] = BPF_LD|BPF_B|BPF_ABS, + [BPF_S_ANC_NLATTR_NEST] = BPF_LD|BPF_B|BPF_ABS, + [BPF_S_ANC_MARK] = BPF_LD|BPF_B|BPF_ABS, + [BPF_S_ANC_QUEUE] = BPF_LD|BPF_B|BPF_ABS, + [BPF_S_ANC_HATYPE] = BPF_LD|BPF_B|BPF_ABS, + [BPF_S_ANC_RXHASH] = BPF_LD|BPF_B|BPF_ABS, + [BPF_S_ANC_CPU] = BPF_LD|BPF_B|BPF_ABS, + [BPF_S_ANC_ALU_XOR_X] = BPF_LD|BPF_B|BPF_ABS, + [BPF_S_ANC_SECCOMP_LD_W] = BPF_LD|BPF_B|BPF_ABS, + [BPF_S_LD_W_LEN] = BPF_LD|BPF_W|BPF_LEN, + [BPF_S_LD_W_IND] = BPF_LD|BPF_W|BPF_IND, + [BPF_S_LD_H_IND] = BPF_LD|BPF_H|BPF_IND, + [BPF_S_LD_B_IND] = BPF_LD|BPF_B|BPF_IND, + [BPF_S_LD_IMM] = BPF_LD|BPF_IMM, + [BPF_S_LDX_W_LEN] = BPF_LDX|BPF_W|BPF_LEN, + [BPF_S_LDX_B_MSH] = BPF_LDX|BPF_B|BPF_MSH, + [BPF_S_LDX_IMM] = BPF_LDX|BPF_IMM, + [BPF_S_MISC_TAX] = BPF_MISC|BPF_TAX, + [BPF_S_MISC_TXA] = BPF_MISC|BPF_TXA, + [BPF_S_RET_K] = BPF_RET|BPF_K, + [BPF_S_RET_A] = BPF_RET|BPF_A, + [BPF_S_ALU_DIV_K] = BPF_ALU|BPF_DIV|BPF_K, + [BPF_S_LD_MEM] = BPF_LD|BPF_MEM, + [BPF_S_LDX_MEM] = BPF_LDX|BPF_MEM, + [BPF_S_ST] = BPF_ST, + [BPF_S_STX] = BPF_STX, + [BPF_S_JMP_JA] = BPF_JMP|BPF_JA, + [BPF_S_JMP_JEQ_K] = BPF_JMP|BPF_JEQ|BPF_K, + [BPF_S_JMP_JEQ_X] = BPF_JMP|BPF_JEQ|BPF_X, + [BPF_S_JMP_JGE_K] = BPF_JMP|BPF_JGE|BPF_K, + [BPF_S_JMP_JGE_X] = BPF_JMP|BPF_JGE|BPF_X, + [BPF_S_JMP_JGT_K] = BPF_JMP|BPF_JGT|BPF_K, + [BPF_S_JMP_JGT_X] = BPF_JMP|BPF_JGT|BPF_X, + [BPF_S_JMP_JSET_K] = BPF_JMP|BPF_JSET|BPF_K, + [BPF_S_JMP_JSET_X] = BPF_JMP|BPF_JSET|BPF_X, + }; + u16 code; + + code = filt->code; + + to->code = decodes[code]; + to->jt = filt->jt; + to->jf = filt->jf; + + if (code == BPF_S_ALU_DIV_K) { + /* + * When loaded this rule user gave us X, which was + * translated into R = r(X). Now we calculate the + * RR = r(R) and report it back. If next time this + * value is loaded and RRR = r(RR) is calculated + * then the R == RRR will be true. + * + * One exception. X == 1 translates into R == 0 and + * we can't calculate RR out of it with r(). + */ + + if (filt->k == 0) + to->k = 1; + else + to->k = reciprocal_value(filt->k); + + BUG_ON(reciprocal_value(to->k) != filt->k); + } else + to->k = filt->k; +} + +int sk_get_filter(struct sock *sk, struct sock_filter __user *ubuf, unsigned int len) +{ + struct sk_filter *filter; + int i, ret; + + lock_sock(sk); + filter = rcu_dereference_protected(sk->sk_filter, + sock_owned_by_user(sk)); + ret = 0; + if (!filter) + goto out; + ret = filter->len; + if (!len) + goto out; + ret = -EINVAL; + if (len < filter->len) + goto out; + + ret = -EFAULT; + for (i = 0; i < filter->len; i++) { + struct sock_filter fb; + + sk_decode_filter(&filter->insns[i], &fb); + if (copy_to_user(&ubuf[i], &fb, sizeof(fb))) + goto out; + } + + ret = filter->len; +out: + release_sock(sk); + return ret; +}
diff --git a/net/core/sock.c b/net/core/sock.c
index 0a023b8..0628600 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c@@ -1077,6 +1077,12 @@ int sock_getsockopt(struct socket *sock, int level, int optname, case SO_BINDTODEVICE: v.val = sk->sk_bound_dev_if; break; + case SO_GET_FILTER: + len = sk_get_filter(sk, (struct sock_filter __user *)optval, len); + if (len < 0) + return len; + + goto lenout; default: return -ENOPROTOOPT; }