flow_dissector_is_valid_access doesn't check that the context access is
aligned. As a consequence, an unaligned access within one of the exposed
field is considered valid and later rejected by
flow_dissector_convert_ctx_access when we try to convert it.
The later rejection is problematic because it's reported as a verifier
bug with a kernel warning and doesn't point to the right instruction in
verifier logs.
Fixes: d58e468b1112 ("flow_dissector: implements flow dissector BPF hook")
Reported-by: syzbot+ccac90e482b2a81d74aa@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://syzkaller.appspot.com/bug?extid=ccac90e482b2a81d74aa
Signed-off-by: Paul Chaignon <paul.chaignon@xxxxxxxxx>
---
net/core/filter.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/net/core/filter.c b/net/core/filter.c
index c09a85c17496..da391e2b0788 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -9458,6 +9458,9 @@ static bool flow_dissector_is_valid_access(int off, int size,
if (off < 0 || off >= sizeof(struct __sk_buff))
return false;
+ if (off % size != 0)
+ return false;
+
if (type == BPF_WRITE)
return false;
--
2.43.0
