diff mbox series

[5.4,064/147] bpf, sockmap: msg_pop_data can incorrecty set an sge length

Message ID 20200518173522.043577325@linuxfoundation.org
State New
Headers show
Series None | expand

Commit Message

Greg Kroah-Hartman May 18, 2020, 5:36 p.m. UTC 
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@john-Precision-5820-Tower
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 net/core/filter.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
diff mbox series

Patch

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;
 		}
 	}