From: Xin Long lucien.xin@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@syzkaller.appspotmail.com Reported-by: syzbot+70a42f45e76bede082be@syzkaller.appspotmail.com Signed-off-by: Xin Long lucien.xin@gmail.com Reviewed-by: Marcelo Ricardo Leitner marcelo.leitner@gmail.com Link: https://patch.msgid.link/dd7dc337b99876d4132d0961f776913719f7d225.1754595611... Signed-off-by: Jakub Kicinski kuba@kernel.org [ kovalev: bp to fix CVE-2025-38718 ] Signed-off-by: Vasiliy Kovalev kovalev@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;