[lvc-project] [PATCH 6.1.y] sctp: linearize cloned gso packets in sctp_rcv

[Vasiliy Kovalev]

From: Xin Long <lucien.xin at gmail.com>

commit fd60d8a086191fe33c2d719732d2482052fa6805 upstream.

A cloned head skb still shares these frag skbs in fraglist with the
original head skb. It's not safe to access these frag skbs.

syzbot reported two use-of-uninitialized-memory bugs caused by this:

  BUG: KMSAN: uninit-value in sctp_inq_pop+0x15b7/0x1920 net/sctp/inqueue.c:211
   sctp_inq_pop+0x15b7/0x1920 net/sctp/inqueue.c:211
   sctp_assoc_bh_rcv+0x1a7/0xc50 net/sctp/associola.c:998
   sctp_inq_push+0x2ef/0x380 net/sctp/inqueue.c:88
   sctp_backlog_rcv+0x397/0xdb0 net/sctp/input.c:331
   sk_backlog_rcv+0x13b/0x420 include/net/sock.h:1122
   __release_sock+0x1da/0x330 net/core/sock.c:3106
   release_sock+0x6b/0x250 net/core/sock.c:3660
   sctp_wait_for_connect+0x487/0x820 net/sctp/socket.c:9360
   sctp_sendmsg_to_asoc+0x1ec1/0x1f00 net/sctp/socket.c:1885
   sctp_sendmsg+0x32b9/0x4a80 net/sctp/socket.c:2031
   inet_sendmsg+0x25a/0x280 net/ipv4/af_inet.c:851
   sock_sendmsg_nosec net/socket.c:718 [inline]

and

  BUG: KMSAN: uninit-value in sctp_assoc_bh_rcv+0x34e/0xbc0 net/sctp/associola.c:987
   sctp_assoc_bh_rcv+0x34e/0xbc0 net/sctp/associola.c:987
   sctp_inq_push+0x2a3/0x350 net/sctp/inqueue.c:88
   sctp_backlog_rcv+0x3c7/0xda0 net/sctp/input.c:331
   sk_backlog_rcv+0x142/0x420 include/net/sock.h:1148
   __release_sock+0x1d3/0x330 net/core/sock.c:3213
   release_sock+0x6b/0x270 net/core/sock.c:3767
   sctp_wait_for_connect+0x458/0x820 net/sctp/socket.c:9367
   sctp_sendmsg_to_asoc+0x223a/0x2260 net/sctp/socket.c:1886
   sctp_sendmsg+0x3910/0x49f0 net/sctp/socket.c:2032
   inet_sendmsg+0x269/0x2a0 net/ipv4/af_inet.c:851
   sock_sendmsg_nosec net/socket.c:712 [inline]

This patch fixes it by linearizing cloned gso packets in sctp_rcv().

Fixes: 90017accff61 ("sctp: Add GSO support")
Reported-by: syzbot+773e51afe420baaf0e2b at syzkaller.appspotmail.com
Reported-by: syzbot+70a42f45e76bede082be at syzkaller.appspotmail.com
Signed-off-by: Xin Long <lucien.xin at gmail.com>
Reviewed-by: Marcelo Ricardo Leitner <marcelo.leitner at gmail.com>
Link: https://patch.msgid.link/dd7dc337b99876d4132d0961f776913719f7d225.1754595611.git.lucien.xin@gmail.com
Signed-off-by: Jakub Kicinski <kuba at kernel.org>
[ kovalev: bp to fix CVE-2025-38718 ]
Signed-off-by: Vasiliy Kovalev <kovalev at altlinux.org>
---
This patch is lost/missing, as it has already been added
into stable branches less than and greater than 6.1.
---
 net/sctp/input.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/sctp/input.c b/net/sctp/input.c
index 4ee9374dcfb9..182898cb754a 100644
--- a/net/sctp/input.c
+++ b/net/sctp/input.c
@@ -114,7 +114,7 @@ int sctp_rcv(struct sk_buff *skb)
 	 * it's better to just linearize it otherwise crc computing
 	 * takes longer.
 	 */
-	if ((!is_gso && skb_linearize(skb)) ||
+	if (((!is_gso || skb_cloned(skb)) && skb_linearize(skb)) ||
 	    !pskb_may_pull(skb, sizeof(struct sctphdr)))
 		goto discard_it;
 
-- 
2.50.1