CVE-2025-38718

In the Linux kernel, the following vulnerability has been resolved:

sctp: linearize cloned gso packets in sctp_rcv

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 sctpinqpop+0x15b7/0x1920 net/sctp/inqueue.c:211 sctpinqpop+0x15b7/0x1920 net/sctp/inqueue.c:211 sctpassocbhrcv+0x1a7/0xc50 net/sctp/associola.c:998 sctpinqpush+0x2ef/0x380 net/sctp/inqueue.c:88 sctpbacklogrcv+0x397/0xdb0 net/sctp/input.c:331 skbacklog_rcv+0x13b/0x420 include/net/sock.h:1122 _releasesock+0x1da/0x330 net/core/sock.c:3106 releasesock+0x6b/0x250 net/core/sock.c:3660 sctpwaitforconnect+0x487/0x820 net/sctp/socket.c:9360 sctpsendmsgtoasoc+0x1ec1/0x1f00 net/sctp/socket.c:1885 sctpsendmsg+0x32b9/0x4a80 net/sctp/socket.c:2031 inetsendmsg+0x25a/0x280 net/ipv4/afinet.c:851 socksendmsgnosec net/socket.c:718 [inline]

and

BUG: KMSAN: uninit-value in sctpassocbhrcv+0x34e/0xbc0 net/sctp/associola.c:987 sctpassocbhrcv+0x34e/0xbc0 net/sctp/associola.c:987 sctpinqpush+0x2a3/0x350 net/sctp/inqueue.c:88 sctpbacklogrcv+0x3c7/0xda0 net/sctp/input.c:331 skbacklogrcv+0x142/0x420 include/net/sock.h:1148 _releasesock+0x1d3/0x330 net/core/sock.c:3213 releasesock+0x6b/0x270 net/core/sock.c:3767 sctpwaitforconnect+0x458/0x820 net/sctp/socket.c:9367 sctpsendmsgtoasoc+0x223a/0x2260 net/sctp/socket.c:1886 sctpsendmsg+0x3910/0x49f0 net/sctp/socket.c:2032 inetsendmsg+0x269/0x2a0 net/ipv4/afinet.c:851 socksendmsgnosec net/socket.c:712 [inline]

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