Subject: [syzbot] [sctp?] UBSAN: shift-out-of-bounds in sctp_transport_update_rto (2)

From: syzbot <[email-masked]>
Date: Thu, 06 Nov 2025 03:08:30 -0800

Hello,

syzbot found the following issue on:

HEAD commit:    c9cfc122f037 Merge tag 'for-6.18-rc4-tag' of git://git.ker..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=17d72114580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=19d831c6d0386a9c
dashboard link: https://syzkaller.appspot.com/bug?extid=f8c46c8b2b7f6e076e99
compiler:       gcc (Debian 12.2.0-14+deb12u1) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/c1699c8b52f1/disk-c9cfc122.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/a1af4e539151/vmlinux-c9cfc122.xz
kernel image: https://storage.googleapis.com/syzbot-assets/771c6be9d72b/bzImage-c9cfc122.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: [email-masked]

------------[ 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 ]---

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