In the Linux kernel, the following vulnerability has been resolved: usb: atm: usbatm: fix invalid ci_range initialization syzbot reported

In the Linux kernel, the following vulnerability has been resolved:

usb: atm: usbatm: fix invalid ci_range initialization

syzbot reported a shift-out-of-bounds in __vcc_connect():

UBSAN: shift-out-of-bounds in net/atm/common.c:382:32
shift exponent -1 is negative
CPU: 0 UID: 0 PID: 5987 Comm: syz.0.18 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Compute Engine/Google Compute Engine, BIOS Google 08/05/2026
Call Trace:
<TASK>
dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
ubsan_epilogue+0xa/0x30 lib/ubsan.c:233
__ubsan_handle_shift_out_of_bounds+0x36d/0x400 lib/ubsan.c:494
__vcc_connect+0x14b4/0x19c0 net/atm/common.c:382
vcc_connect+0x328/0x8f0 net/atm/common.c:498
pvc_bind+0x272/0x380 net/atm/pvc.c:52
__sys_bind+0x2e3/0x410 net/socket.c:1976
__x64_sys_bind+0x7a/0x90 net/socket.c:1979
...

ATM device ci_range fields (vpi_bits and vci_bits) represent the
number of bits supported for VPI and VCI addressing on the device.
net/atm/common.c directly uses these fields as bit shift counts:
vpi >> dev->ci_range.vpi_bits
vci >> dev->ci_range.vci_bits
1 << vcc->dev->ci_range.vpi_bits
1 << vcc->dev->ci_range.vci_bits

usbatm_atm_init() sets ci_range.vpi_bits and ci_range.vci_bits to
ATM_CI_MAX (-1), which is defined in <uapi/linux/atmdev.h> as a
sentinel value for userspace ATM_SETCIRANGE requests, not a valid bit
count. Shifting by -1 is undefined behavior and triggers UBSAN
warnings.

ATM UNI cell headers allow up to 8 bits for VPI (0..255) and 16 bits
for VCI (0..65535). Initialize vpi_bits to 8 and vci_bits to 16, as
done by solos-pci.