[v6.1] UBSAN: shift-out-of-bounds in __vcc_connect

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: e4f7d8be268e Linux 6.1.182
git tree: linux-6.1.y
console output: https://syzkaller.appspot.com/x/log.txt?x=13e2d149580000
kernel config: https://syzkaller.appspot.com/x/.config?x=31dfefc4a14efea3
dashboard link: https://syzkaller.appspot.com/bug?extid=27621bbad59218d4af8b
compiler: Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/156843a60452/disk-e4f7d8be.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/719d532a0151/vmlinux-e4f7d8be.xz
kernel image: https://storage.googleapis.com/syzbot-assets/12160bc2f9ec/bzImage-e4f7d8be.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+27621b...@syzkaller.appspotmail.com

================================================================================
UBSAN: shift-out-of-bounds in net/atm/common.c:389:10
shift exponent -1 is negative
CPU: 0 PID: 4717 Comm: syz.2.115 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
Call Trace:
<TASK>
dump_stack_lvl+0x188/0x24e lib/dump_stack.c:106
ubsan_epilogue+0xa/0x30 lib/ubsan.c:151
__ubsan_handle_shift_out_of_bounds+0x364/0x3f0 lib/ubsan.c:321
__vcc_connect+0x11b7/0x1600 net/atm/common.c:389
vcc_connect+0x31f/0x880 net/atm/common.c:510
pvc_bind+0x262/0x370 net/atm/pvc.c:52
__sys_bind+0x2e9/0x3e0 net/socket.c:1811
__do_sys_bind net/socket.c:1822 [inline]
__se_sys_bind net/socket.c:1820 [inline]
__x64_sys_bind+0x76/0x80 net/socket.c:1820
do_syscall_x64 arch/x86/entry/common.c:46 [inline]
do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:76
entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7fe07e79e0d9
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 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 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fe07f658028 EFLAGS: 00000246 ORIG_RAX: 0000000000000031
RAX: ffffffffffffffda RBX: 00007fe07ea25fa0 RCX: 00007fe07e79e0d9
RDX: 000000000000000c RSI: 0000200000000300 RDI: 0000000000000003
RBP: 00007fe07e835024 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fe07ea26038 R14: 00007fe07ea25fa0 R15: 00007fff80420378
</TASK>
================================================================================


---
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[syzbot]

syzbot has found a reproducer for the following issue on:

HEAD commit: e4f7d8be268e Linux 6.1.182
git tree: linux-6.1.y

console output: https://syzkaller.appspot.com/x/log.txt?x=16f28a25580000

kernel config: https://syzkaller.appspot.com/x/.config?x=31dfefc4a14efea3
dashboard link: https://syzkaller.appspot.com/bug?extid=27621bbad59218d4af8b
compiler: Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8

syz repro: https://syzkaller.appspot.com/x/repro.syz?x=17510279580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/156843a60452/disk-e4f7d8be.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/719d532a0151/vmlinux-e4f7d8be.xz
kernel image: https://storage.googleapis.com/syzbot-assets/12160bc2f9ec/bzImage-e4f7d8be.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+27621b...@syzkaller.appspotmail.com

================================================================================
UBSAN: shift-out-of-bounds in net/atm/common.c:389:10
shift exponent -1 is negative

CPU: 1 PID: 4433 Comm: syz.0.17 Not tainted syzkaller #0

Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
Call Trace:
<TASK>
dump_stack_lvl+0x188/0x24e lib/dump_stack.c:106
ubsan_epilogue+0xa/0x30 lib/ubsan.c:151
__ubsan_handle_shift_out_of_bounds+0x364/0x3f0 lib/ubsan.c:321
__vcc_connect+0x11b7/0x1600 net/atm/common.c:389
vcc_connect+0x31f/0x880 net/atm/common.c:510
pvc_bind+0x262/0x370 net/atm/pvc.c:52
__sys_bind+0x2e9/0x3e0 net/socket.c:1811
__do_sys_bind net/socket.c:1822 [inline]
__se_sys_bind net/socket.c:1820 [inline]
__x64_sys_bind+0x76/0x80 net/socket.c:1820
do_syscall_x64 arch/x86/entry/common.c:46 [inline]
do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:76
entry_SYSCALL_64_after_hwframe+0x68/0xd2

RIP: 0033:0x7f6a67d9e0d9

Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 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 e8 ff ff ff f7 d8 64 89 01 48

RSP: 002b:00007ffcce950828 EFLAGS: 00000246 ORIG_RAX: 0000000000000031
RAX: ffffffffffffffda RBX: 00007f6a68025fa0 RCX: 00007f6a67d9e0d9
RDX: 000000000000000c RSI: 0000200000000300 RDI: 0000000000000004
RBP: 00007f6a67e35024 R08: 0000000000000000 R09: 0000000000000000

R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000

R13: 00007f6a68025fac R14: 00007f6a68025fa0 R15: 00007f6a68025fa0
</TASK>
================================================================================


---
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