CVE-2026-90055usb: atm: usbatm: fix invalid ci_range initialization

Official description

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.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/8442586526c406527bf31206e538c0ce6bc672e6
• https://git.kernel.org/stable/c/561cbd6d49022c9a383e22a39c87a165a4d39f9c
• https://git.kernel.org/stable/c/76bc7c3a44856744b64aa91d9afe6d9522a78c42
• https://git.kernel.org/stable/c/7baa0c92be39eb3da755ed6f200497a57078c47b
• https://git.kernel.org/stable/c/1e964d414bfd9f8dfe9948d08e4b9dda4ed2e422
• https://git.kernel.org/stable/c/ff7f77a234f7b74e5955a6e34fa74eca4c9ca44c
• https://git.kernel.org/stable/c/75667703115154a4fd9cf259d4f826d8729cbcda
• https://git.kernel.org/stable/c/a60fd8c6dbaa76da4163cf225ed2b9e982540f39