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authorDaniel Borkmann <dborkman@redhat.com>2014-04-05 03:04:03 +0400
committerDavid S. Miller <davem@davemloft.net>2014-04-07 20:54:39 +0400
commit5f9fde5f799df7156eeb3fa58282e9fd2f38a5f8 (patch)
tree26556f3c6534b9f725615d7db4a3772338add528 /net
parentd80e773f16f66a610e04f6875d4da84e74a8fb6c (diff)
downloadlinux-5f9fde5f799df7156eeb3fa58282e9fd2f38a5f8.tar.xz
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 <dborkman@redhat.com> Reviewed-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net')
-rw-r--r--net/core/filter.c32
1 files changed, 16 insertions, 16 deletions
diff --git a/net/core/filter.c b/net/core/filter.c
index 765556ba32ef..e08b3822c72a 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: