From: Eric Dumazet edumazet@google.com

[ Upstream commit 10206302af856791fbcc27a33ed3c3eb09b2793d ]

We must serialize calls to sctp_udp_sock_stop() and sctp_udp_sock_start() or risk a crash as syzbot reported:

Oops: general protection fault, probably for non-canonical address 0xdffffc000000000d: 0000 [#1] SMP KASAN PTI KASAN: null-ptr-deref in range [0x0000000000000068-0x000000000000006f] CPU: 1 UID: 0 PID: 6551 Comm: syz.1.44 Not tainted 6.14.0-syzkaller-g7f2ff7b62617 #0 PREEMPT(full) Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2025 RIP: 0010:kernel_sock_shutdown+0x47/0x70 net/socket.c:3653 Call Trace: <TASK> udp_tunnel_sock_release+0x68/0x80 net/ipv4/udp_tunnel_core.c:181 sctp_udp_sock_stop+0x71/0x160 net/sctp/protocol.c:930 proc_sctp_do_udp_port+0x264/0x450 net/sctp/sysctl.c:553 proc_sys_call_handler+0x3d0/0x5b0 fs/proc/proc_sysctl.c:601 iter_file_splice_write+0x91c/0x1150 fs/splice.c:738 do_splice_from fs/splice.c:935 [inline] direct_splice_actor+0x18f/0x6c0 fs/splice.c:1158 splice_direct_to_actor+0x342/0xa30 fs/splice.c:1102 do_splice_direct_actor fs/splice.c:1201 [inline] do_splice_direct+0x174/0x240 fs/splice.c:1227 do_sendfile+0xafd/0xe50 fs/read_write.c:1368 __do_sys_sendfile64 fs/read_write.c:1429 [inline] __se_sys_sendfile64 fs/read_write.c:1415 [inline] __x64_sys_sendfile64+0x1d8/0x220 fs/read_write.c:1415 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]

Fixes: 046c052b475e ("sctp: enable udp tunneling socks") Reported-by: syzbot+fae49d997eb56fa7c74d@syzkaller.appspotmail.com Closes: https://lore.kernel.org/netdev/67ea5c01.050a0220.1547ec.012b.GAE@google.com/... Signed-off-by: Eric Dumazet edumazet@google.com Cc: Marcelo Ricardo Leitner marcelo.leitner@gmail.com Acked-by: Xin Long lucien.xin@gmail.com Link: https://patch.msgid.link/20250331091532.224982-1-edumazet@google.com Signed-off-by: Jakub Kicinski kuba@kernel.org [Minor conflict resolved due to code context change.] Signed-off-by: Jianqi Ren jianqi.ren.cn@windriver.com Signed-off-by: He Zhe zhe.he@windriver.com --- Verified the build test --- net/sctp/sysctl.c | 4 ++++ 1 file changed, 4 insertions(+)

diff --git a/net/sctp/sysctl.c b/net/sctp/sysctl.c index 916dc2e81e42..f3d09998c24d 100644 --- a/net/sctp/sysctl.c +++ b/net/sctp/sysctl.c @@ -518,6 +518,8 @@ static int proc_sctp_do_auth(struct ctl_table *ctl, int write, return ret; }

+static DEFINE_MUTEX(sctp_sysctl_mutex); + static int proc_sctp_do_udp_port(struct ctl_table *ctl, int write, void *buffer, size_t *lenp, loff_t *ppos) { @@ -542,6 +544,7 @@ static int proc_sctp_do_udp_port(struct ctl_table *ctl, int write, if (new_value > max || new_value < min) return -EINVAL;

+ mutex_lock(&sctp_sysctl_mutex); net->sctp.udp_port = new_value; sctp_udp_sock_stop(net); if (new_value) { @@ -554,6 +557,7 @@ static int proc_sctp_do_udp_port(struct ctl_table *ctl, int write, lock_sock(sk); sctp_sk(sk)->udp_port = htons(net->sctp.udp_port); release_sock(sk); + mutex_unlock(&sctp_sysctl_mutex); }

return ret;