CVE-2021-47497

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

nvmem: Fix shift-out-of-bound (UBSAN) with byte size cells

If a cell has nbits equal to a multiple of BITS_PER_BYTE the logic

*p &= GENMASK((cell->nbits%BITS_PER_BYTE) - 1, 0);

will become undefined behavior because nbits modulo BITS_PER_BYTE is 0, and we subtract one from that making a large number that is then shifted more than the number of bits that fit into an unsigned long.

UBSAN reports this problem:

UBSAN: shift-out-of-bounds in drivers/nvmem/core.c:1386:8 shift exponent 64 is too large for 64-bit type unsigned long CPU: 6 PID: 7 Comm: kworker/u16:0 Not tainted 5.15.0-rc3+ #9 Hardware name: Google Lazor (rev3+) with KB Backlight (DT) Workqueue: events_unbound deferred_probe_work_func Call trace: dump_backtrace+0x0/0x170 show_stack+0x24/0x30 dump_stack_lvl+0x64/0x7c dump_stack+0x18/0x38 ubsan_epilogue+0x10/0x54 __ubsan_handle_shift_out_of_bounds+0x180/0x194 __nvmem_cell_read+0x1ec/0x21c nvmem_cell_read+0x58/0x94 nvmem_cell_read_variable_common+0x4c/0xb0 nvmem_cell_read_variable_le_u32+0x40/0x100 a6xx_gpu_init+0x170/0x2f4 adreno_bind+0x174/0x284 component_bind_all+0xf0/0x264 msm_drm_bind+0x1d8/0x7a0 try_to_bring_up_master+0x164/0x1ac __component_add+0xbc/0x13c component_add+0x20/0x2c dp_display_probe+0x340/0x384 platform_probe+0xc0/0x100 really_probe+0x110/0x304 __driver_probe_device+0xb8/0x120 driver_probe_device+0x4c/0xfc __device_attach_driver+0xb0/0x128 bus_for_each_drv+0x90/0xdc __device_attach+0xc8/0x174 device_initial_probe+0x20/0x2c bus_probe_device+0x40/0xa4 deferred_probe_work_func+0x7c/0xb8 process_one_work+0x128/0x21c process_scheduled_works+0x40/0x54 worker_thread+0x1ec/0x2a8 kthread+0x138/0x158 ret_from_fork+0x10/0x20

Fix it by making sure there are any bits to mask out.

Affected Software

References

• https://git.kernel.org/stable/c/0594f1d048d8dc338eb9a240021b1d00ae1eb082
• https://git.kernel.org/stable/c/0e822e5413da1af28cca350cb1cb42b6133bdcae
• https://git.kernel.org/stable/c/2df6c023050205c4d04ffc121bc549f65cb8d1df
• https://git.kernel.org/stable/c/57e48886401b14cd351423fabfec2cfd18df4f66
• https://git.kernel.org/stable/c/5d388fa01fa6eb310ac023a363a6cb216d9d8fe9
• https://git.kernel.org/stable/c/60df06bbdf497e37ed25ad40572c362e5b0998df
• https://git.kernel.org/stable/c/abcb8d33e4d2215ccde5ab5ccf9f730a59d79d97
• https://git.kernel.org/stable/c/eb0fc8e7170e61eaf65d28dee4a8baf4e86b19ca