[syzbot] [net?] [usb?] UBSAN: shift-out-of-bounds in vcc_connect

[syzbot] [net?] [usb?] UBSAN: shift-out-of-bounds in vcc_connect

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    bd5f485f3f02 Merge tag 'soc-arm-7.3' of git://git.kernel.o..
git tree:       upstream
console+strace: https://syzkaller.appspot.com/x/log.txt?x=16736e79580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=6d6c2a05eaadaf10
dashboard link: https://syzkaller.appspot.com/bug?extid=6665d3db5fef15914802
compiler:       gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=133f2549580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/2da33ef8d789/disk-bd5f485f.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/7e8921e0c1e1/vmlinux-bd5f485f.xz
kernel image: https://storage.googleapis.com/syzbot-assets/c7e5335b79c8/bzImage-bd5f485f.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+6665d3db5fef15914802@syzkaller.appspotmail.com

------------[ cut here ]------------
UBSAN: shift-out-of-bounds in net/atm/common.c:381:10
shift exponent -1 is negative
CPU: 0 UID: 0 PID: 6073 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/16/2026
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x100/0x190 lib/dump_stack.c:120
 ubsan_epilogue+0xa/0x30 lib/ubsan.c:233
 __ubsan_handle_shift_out_of_bounds+0x279/0x2a0 lib/ubsan.c:494
 __vcc_connect net/atm/common.c:381 [inline]
 vcc_connect.cold+0xe0/0x123 net/atm/common.c:498
 pvc_bind+0x33f/0x460 net/atm/pvc.c:52
 __sys_bind_socket net/socket.c:1945 [inline]
 __sys_bind_socket net/socket.c:1937 [inline]
 __sys_bind+0x1a9/0x260 net/socket.c:1976
 __do_sys_bind net/socket.c:1981 [inline]
 __se_sys_bind net/socket.c:1979 [inline]
 __x64_sys_bind+0x72/0xb0 net/socket.c:1979
 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
 do_syscall_64+0x123/0x790 arch/x86/entry/syscall_64.c:84
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f6a3099e0d9
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:00007fff44bcea08 EFLAGS: 00000246 ORIG_RAX: 0000000000000031
RAX: ffffffffffffffda RBX: 00007f6a30c25fa0 RCX: 00007f6a3099e0d9
RDX: 000000000000000c RSI: 0000200000000100 RDI: 0000000000000004
RBP: 00007f6a30a35024 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f6a30c25fac R14: 00007f6a30c25fa0 R15: 00007f6a30c25fa0
 </TASK>
---[ end trace ]---


---
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Forwarded: [PATCH] net: atm: fix shift-out-of-bounds in __vcc_connect()

[syzbot]

For archival purposes, forwarding an incoming command email to
linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com.

***

Subject: [PATCH] net: atm: fix shift-out-of-bounds in __vcc_connect()
Author: kartikey406@gmail.com

#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master


dev->ci_range.vpi_bits and vci_bits can legitimately be ATM_CI_MAX (-1),
a sentinel meaning "no range configured, use maximum" (see
include/uapi/linux/atmdev.h). Some drivers, such as usbatm_atm_init()
in drivers/usb/atm/usbatm.c, set this sentinel and never resolve it to
an actual bit width.

__vcc_connect() uses these fields directly as a shift amount without
checking for the sentinel, so binding a PVC socket on such a device
triggers a negative shift:

  UBSAN: shift-out-of-bounds in net/atm/common.c:381:10
  shift exponent -1 is negative

Skip the range check when ci_range.vpi_bits/vci_bits is still
ATM_CI_MAX, since that value means "unrestricted".

Reported-by: syzbot+6665d3db5fef15914802@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=6665d3db5fef15914802
Signed-off-by: Deepanshu Kartikey <kartikey406@gmail.com>
---
 net/atm/common.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/net/atm/common.c b/net/atm/common.c
index 81195727fa18..73057bb016f7 100644
--- a/net/atm/common.c
+++ b/net/atm/common.c
@@ -378,8 +378,11 @@ static int __vcc_connect(struct atm_vcc *vcc, struct atm_dev *dev, short vpi,
 	int error;
 
 	if ((vpi != ATM_VPI_UNSPEC && vpi != ATM_VPI_ANY &&
+	    dev->ci_range.vpi_bits != ATM_CI_MAX &&
 	    vpi >> dev->ci_range.vpi_bits) || (vci != ATM_VCI_UNSPEC &&
-	    vci != ATM_VCI_ANY && vci >> dev->ci_range.vci_bits))
+	    vci != ATM_VCI_ANY &&
+	    dev->ci_range.vci_bits != ATM_CI_MAX &&
+	    vci >> dev->ci_range.vci_bits))
 		return -EINVAL;
 	if (vci > 0 && vci < ATM_NOT_RSV_VCI && !capable(CAP_NET_BIND_SERVICE))
 		return -EPERM;
-- 
2.34.1

Re: [syzbot] [net?] [usb?] UBSAN: shift-out-of-bounds in vcc_connect

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-by: syzbot+6665d3db5fef15914802@syzkaller.appspotmail.com
Tested-by: syzbot+6665d3db5fef15914802@syzkaller.appspotmail.com

Tested on:

commit:         4352b8ae Merge tag 'i3c/for-7.3' of git://git.kernel.o..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=12523549580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=a7b54093c8b7a894
dashboard link: https://syzkaller.appspot.com/bug?extid=6665d3db5fef15914802
compiler:       gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44
patch:          https://syzkaller.appspot.com/x/patch.diff?x=16682625580000

Note: testing is done by a robot and is best-effort only.