[PATCH net] sctp: validate STALE_COOKIE cause length before reading staleness
From: Weiming Shi <hidden>
Date: 2026-07-04 03:35:59
Also in:
linux-sctp, stable
Subsystem:
networking [general], sctp protocol, the rest · Maintainers:
"David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Marcelo Ricardo Leitner, Xin Long, Linus Torvalds
When an ERROR chunk with a STALE_COOKIE cause is received in the
COOKIE_ECHOED state, sctp_sf_do_5_2_6_stale() reads the 4-byte Measure
of Staleness that follows the cause header:
err = (struct sctp_errhdr *)(chunk->skb->data);
stale = ntohl(*(__be32 *)((u8 *)err + sizeof(*err)));
err is the first cause in the chunk, not the STALE_COOKIE cause that
caused the dispatch, and nothing guarantees the staleness field is
present. sctp_walk_errors() only requires a cause to be as long as the
4-byte header, so for a STALE_COOKIE cause of length 4 the read runs
past the cause, and for a minimal ERROR chunk past skb->tail. The value
is echoed to the peer in the Cookie Preservative of the reply INIT,
leaking uninitialized memory.
sctp_sf_cookie_echoed_err() already walks to the STALE_COOKIE cause, so
check its length there and pass it to sctp_sf_do_5_2_6_stale(), which
reads that cause instead of the first one. A STALE_COOKIE cause too
short to hold the staleness field is discarded.
The read is reachable by any peer that can drive an association into
COOKIE_ECHOED, including an unprivileged process using a raw SCTP socket
in a user and network namespace.
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Reported-by: Xiang Mei <redacted>
Assisted-by: Claude:claude-opus-4-8
Cc: stable@vger.kernel.org
Signed-off-by: Weiming Shi <redacted>
---
net/sctp/sm_statefuns.c | 23 ++++++++++++++---------
1 file changed, 14 insertions(+), 9 deletions(-)
diff --git a/net/sctp/sm_statefuns.c b/net/sctp/sm_statefuns.c
index d23d935e128e..3893b44448b3 100644
--- a/net/sctp/sm_statefuns.c
+++ b/net/sctp/sm_statefuns.c@@ -74,7 +74,8 @@ static enum sctp_disposition sctp_sf_do_5_2_6_stale( const struct sctp_association *asoc, const union sctp_subtype type, void *arg, - struct sctp_cmd_seq *commands); + struct sctp_cmd_seq *commands, + struct sctp_errhdr *err); static enum sctp_disposition sctp_sf_shut_8_4_5( struct net *net, const struct sctp_endpoint *ep,
@@ -2529,9 +2530,15 @@ enum sctp_disposition sctp_sf_cookie_echoed_err( * errors. */ sctp_walk_errors(err, chunk->chunk_hdr) { - if (SCTP_ERROR_STALE_COOKIE == err->cause) - return sctp_sf_do_5_2_6_stale(net, ep, asoc, type, - arg, commands); + if (err->cause != SCTP_ERROR_STALE_COOKIE) + continue; + /* The staleness is only meaningful if the cause is long + * enough to hold it; a shorter one is malformed. + */ + if (ntohs(err->length) < sizeof(*err) + sizeof(__be32)) + break; + return sctp_sf_do_5_2_6_stale(net, ep, asoc, type, + arg, commands, err); } /* It is possible to have malformed error causes, and that
@@ -2573,13 +2580,13 @@ static enum sctp_disposition sctp_sf_do_5_2_6_stale( const struct sctp_association *asoc, const union sctp_subtype type, void *arg, - struct sctp_cmd_seq *commands) + struct sctp_cmd_seq *commands, + struct sctp_errhdr *err) { int attempts = asoc->init_err_counter + 1; - struct sctp_chunk *chunk = arg, *reply; struct sctp_cookie_preserve_param bht; struct sctp_bind_addr *bp; - struct sctp_errhdr *err; + struct sctp_chunk *reply; u32 stale; if (attempts > asoc->max_init_attempts) {
@@ -2590,8 +2597,6 @@ static enum sctp_disposition sctp_sf_do_5_2_6_stale( return SCTP_DISPOSITION_DELETE_TCB; } - err = (struct sctp_errhdr *)(chunk->skb->data); - /* When calculating the time extension, an implementation * SHOULD use the RTT information measured based on the * previous COOKIE ECHO / ERROR exchange, and should add no
--
2.43.0