From 5f9fde5f799df7156eeb3fa58282e9fd2f38a5f8 Mon Sep 17 00:00:00 2001 From: Daniel Borkmann Date: Sat, 5 Apr 2014 01:04:03 +0200 Subject: [PATCH] net: filter: be more defensive on div/mod by X==0 The old interpreter behaviour was that we returned with 0 whenever we found a division by 0 would take place. In the new interpreter we would currently just skip that instead and continue execution. It's true that a value of 0 as return might not be appropriate in all cases, but current users (socket filters -> drop packet, seccomp -> SECCOMP_RET_KILL, cls_bpf -> unclassified, etc) seem fine with that behaviour. Better this than undefined BPF program behaviour as it's expected that A contains the result of the division. In future, as more use cases open up, we could further adapt this return value to our needs, if necessary. So reintroduce return of 0 for division by 0 as in the old interpreter. Also in case of K which is guaranteed to be 32bit wide, sk_chk_filter() already takes care of preventing division by 0 invoked through K, so we can generally spare us these tests. Signed-off-by: Daniel Borkmann Reviewed-by: Alexei Starovoitov Signed-off-by: David S. Miller --- net/core/filter.c | 32 ++++++++++++++++---------------- 1 file changed, 16 insertions(+), 16 deletions(-) diff --git a/net/core/filter.c b/net/core/filter.c index 765556b..e08b382 100644 --- a/net/core/filter.c +++ b/net/core/filter.c @@ -295,43 +295,43 @@ select_insn: (*(s64 *) &A) >>= K; CONT; BPF_ALU64_BPF_MOD_BPF_X: + if (unlikely(X == 0)) + return 0; tmp = A; - if (X) - A = do_div(tmp, X); + A = do_div(tmp, X); CONT; BPF_ALU_BPF_MOD_BPF_X: + if (unlikely(X == 0)) + return 0; tmp = (u32) A; - if (X) - A = do_div(tmp, (u32) X); + A = do_div(tmp, (u32) X); CONT; BPF_ALU64_BPF_MOD_BPF_K: tmp = A; - if (K) - A = do_div(tmp, K); + A = do_div(tmp, K); CONT; BPF_ALU_BPF_MOD_BPF_K: tmp = (u32) A; - if (K) - A = do_div(tmp, (u32) K); + A = do_div(tmp, (u32) K); CONT; BPF_ALU64_BPF_DIV_BPF_X: - if (X) - do_div(A, X); + if (unlikely(X == 0)) + return 0; + do_div(A, X); CONT; BPF_ALU_BPF_DIV_BPF_X: + if (unlikely(X == 0)) + return 0; tmp = (u32) A; - if (X) - do_div(tmp, (u32) X); + do_div(tmp, (u32) X); A = (u32) tmp; CONT; BPF_ALU64_BPF_DIV_BPF_K: - if (K) - do_div(A, K); + do_div(A, K); CONT; BPF_ALU_BPF_DIV_BPF_K: tmp = (u32) A; - if (K) - do_div(tmp, (u32) K); + do_div(tmp, (u32) K); A = (u32) tmp; CONT; BPF_ALU_BPF_END_BPF_TO_BE: -- 2.7.4