UBSAN: shift-out-of-bounds in sctp_transport_update

UBSAN: shift-out-of-bounds in sctp_transport_update_rto (2)

Status: upstream: reported on 2025/11/06 11:08
Subsystems: sctp
[Documentation on labels]
Reported-by: syzbot+f8c46c8b2b7f6e076e99@syzkaller.appspotmail.com
Fix commit: 1534ff77757e sctp: prevent possible shift-out-of-bounds in sctp_transport_update_rto
Patched on: [ci-qemu-gce-upstream-auto ci-qemu-upstream ci-qemu-upstream-386 ci-qemu2-arm32 ci-qemu2-arm64 ci-qemu2-arm64-compat ci-qemu2-arm64-mte ci-qemu2-riscv64 ci-snapshot-upstream-root ci-upstream-bpf-kasan-gce ci-upstream-bpf-next-kasan-gce ci-upstream-gce-arm64 ci-upstream-gce-leak ci-upstream-kasan-badwrites-root ci-upstream-kasan-gce ci-upstream-kasan-gce-386 ci-upstream-kasan-gce-root ci-upstream-kasan-gce-selinux-root ci-upstream-kasan-gce-smack-root ci-upstream-kmsan-gce-386-root ci-upstream-kmsan-gce-root ci-upstream-linux-next-kasan-gce-root ci-upstream-net-kasan-gce ci-upstream-net-this-kasan-gce ci-upstream-rust-kasan-gce ci2-upstream-fs ci2-upstream-kcsan-gce ci2-upstream-usb], missing on: [ci-qemu-native-arm64-kvm]
First crash: 49d, last: 49d

▶ ▼ Discussions (3)

Title	Replies (including bot)	Last reply
[PATCH net] sctp: prevent possible shift-out-of-bounds in sctp_transport_update_rto	5 (5)	2025/11/11 00:30
Re: [PATCH net] sctp: prevent possible shift-out-of-bounds in sctp_transport_update_rto	2 (2)	2025/11/10 16:28
[syzbot] [sctp?] UBSAN: shift-out-of-bounds in sctp_transport_update_rto (2)	0 (1)	2025/11/06 11:08

▶ ▼ Similar bugs (1)

Kernel	Title	Rank 🛈	Repro	Cause bisect	Fix bisect	Count	Last	Reported	Patched	Status
upstream	UBSAN: shift-out-of-bounds in sctp_transport_update_rto sctp	-1				1	159d	156d	0/29	auto-obsoleted due to no activity on 2025/10/26 07:28

Sample crash report:

------------[ cut here ]------------
UBSAN: shift-out-of-bounds in net/sctp/transport.c:509:41
shift exponent 64 is too large for 32-bit type 'unsigned int'
CPU: 0 UID: 0 PID: 16704 Comm: syz.2.2320 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x16c/0x1f0 lib/dump_stack.c:120
 ubsan_epilogue lib/ubsan.c:233 [inline]
 __ubsan_handle_shift_out_of_bounds+0x27f/0x420 lib/ubsan.c:494
 sctp_transport_update_rto.cold+0x1c/0x34b net/sctp/transport.c:509
 sctp_check_transmitted+0x11c4/0x1c30 net/sctp/outqueue.c:1502
 sctp_outq_sack+0x4ef/0x1b20 net/sctp/outqueue.c:1338
 sctp_cmd_process_sack net/sctp/sm_sideeffect.c:840 [inline]
 sctp_cmd_interpreter net/sctp/sm_sideeffect.c:1372 [inline]
 sctp_side_effects net/sctp/sm_sideeffect.c:1204 [inline]
 sctp_do_sm+0x36df/0x5c80 net/sctp/sm_sideeffect.c:1175
 sctp_assoc_bh_rcv+0x392/0x6f0 net/sctp/associola.c:1034
 sctp_inq_push+0x1db/0x270 net/sctp/inqueue.c:88
 sctp_backlog_rcv+0x169/0x590 net/sctp/input.c:331
 sk_backlog_rcv include/net/sock.h:1158 [inline]
 __release_sock+0x3a9/0x450 net/core/sock.c:3180
 release_sock+0x5a/0x220 net/core/sock.c:3735
 sctp_sendmsg+0xeb9/0x1e00 net/sctp/socket.c:2036
 inet_sendmsg+0x11c/0x140 net/ipv4/af_inet.c:853
 sock_sendmsg_nosec net/socket.c:727 [inline]
 __sock_sendmsg net/socket.c:742 [inline]
 sock_write_iter+0x509/0x610 net/socket.c:1195
 new_sync_write fs/read_write.c:593 [inline]
 vfs_write+0x7d3/0x11d0 fs/read_write.c:686
 ksys_write+0x1f8/0x250 fs/read_write.c:738
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xcd/0xfa0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f3e92f8f6c9
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f3e93e34038 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007f3e931e6090 RCX: 00007f3e92f8f6c9
RDX: 000000000000fdef RSI: 0000000000000000 RDI: 0000000000000003
RBP: 00007f3e93011f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f3e931e6128 R14: 00007f3e931e6090 R15: 00007ffc44d78078
 </TASK>
---[ end trace ]---

Crashes (1):
Time	Kernel	Commit	Syzkaller	Config	Log	Report	Syz repro	C repro	VM info	Assets (help?)	Manager	Title
2025/11/05 04:16	upstream	c9cfc122f037	a6c9c731	.config	console log	report			info	[disk image] [vmlinux] [kernel image]	ci-qemu-gce-upstream-auto	UBSAN: shift-out-of-bounds in sctp_transport_update_rto

* ~~Struck through~~ repros no longer work on HEAD.