From: John Fastabend john.fastabend@gmail.com
[ Upstream commit 3e104c23816220919ea1b3fd93fabe363c67c484 ]
When sk_msg_pop() is called where the pop operation is working on the end of a sge element and there is no additional trailing data and there _is_ data in front of pop, like the following case,
|____________a_____________|__pop__|
We have out of order operations where we incorrectly set the pop variable so that instead of zero'ing pop we incorrectly leave it untouched, effectively. This can cause later logic to shift the buffers around believing it should pop extra space. The result is we have 'popped' more data then we expected potentially breaking program logic.
It took us a while to hit this case because typically we pop headers which seem to rarely be at the end of a scatterlist elements but we can't rely on this.
Fixes: 7246d8ed4dcce ("bpf: helper to pop data from messages") Signed-off-by: John Fastabend john.fastabend@gmail.com Signed-off-by: Daniel Borkmann daniel@iogearbox.net Reviewed-by: Jakub Sitnicki jakub@cloudflare.com Acked-by: Martin KaFai Lau kafai@fb.com Link: https://lore.kernel.org/bpf/158861288359.14306.7654891716919968144.stgit@joh... Signed-off-by: Sasha Levin sashal@kernel.org --- net/core/filter.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/net/core/filter.c b/net/core/filter.c index d59dbc88fef5d..f1f2304822e3b 100644 --- a/net/core/filter.c +++ b/net/core/filter.c @@ -2590,8 +2590,8 @@ BPF_CALL_4(bpf_msg_pop_data, struct sk_msg *, msg, u32, start, } pop = 0; } else if (pop >= sge->length - a) { - sge->length = a; pop -= (sge->length - a); + sge->length = a; } }