Vulnerability CVE-2024-44981
Published: 2024-09-04

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

workqueue: Fix UBSAN 'subtraction overflow' error in shift_and_mask()

UBSAN reports the following 'subtraction overflow' error when booting
in a virtual machine on Android:

| Internal error: UBSAN: integer subtraction overflow: 00000000f2005515 [#1] PREEMPT SMP
| Modules linked in:
| CPU: 0 PID: 1 Comm: swapper/0 Not tainted 6.10.0-00006-g3cbe9e5abd46-dirty #4
| Hardware name: linux,dummy-virt (DT)
| pstate: 600000c5 (nZCv daIF -PAN -UAO -TCO -DIT -SSBS BTYPE=--)
| pc : cancel_delayed_work+0x34/0x44
| lr : cancel_delayed_work+0x2c/0x44
| sp : ffff80008002ba60
| x29: ffff80008002ba60 x28: 0000000000000000 x27: 0000000000000000
| x26: 0000000000000000 x25: 0000000000000000 x24: 0000000000000000
| x23: 0000000000000000 x22: 0000000000000000 x21: ffff1f65014cd3c0
| x20: ffffc0e84c9d0da0 x19: ffffc0e84cab3558 x18: ffff800080009058
| x17: 00000000247ee1f8 x16: 00000000247ee1f8 x15: 00000000bdcb279d
| x14: 0000000000000001 x13: 0000000000000075 x12: 00000a0000000000
| x11: ffff1f6501499018 x10: 00984901651fffff x9 : ffff5e7cc35af000
| x8 : 0000000000000001 x7 : 3d4d455453595342 x6 : 000000004e514553
| x5 : ffff1f6501499265 x4 : ffff1f650ff60b10 x3 : 0000000000000620
| x2 : ffff80008002ba78 x1 : 0000000000000000 x0 : 0000000000000000
| Call trace:
| cancel_delayed_work+0x34/0x44
| deferred_probe_extend_timeout+0x20/0x70
| driver_register+0xa8/0x110
| __platform_driver_register+0x28/0x3c
| syscon_init+0x24/0x38
| do_one_initcall+0xe4/0x338
| do_initcall_level+0xac/0x178
| do_initcalls+0x5c/0xa0
| do_basic_setup+0x20/0x30
| kernel_init_freeable+0x8c/0xf8
| kernel_init+0x28/0x1b4
| ret_from_fork+0x10/0x20
| Code: f9000fbf 97fffa2f 39400268 37100048 (d42aa2a0)
| ---[ end trace 0000000000000000 ]---
| Kernel panic - not syncing: UBSAN: integer subtraction overflow: Fatal exception

This is due to shift_and_mask() using a signed immediate to construct
the mask and being called with a shift of 31 (WORK_OFFQ_POOL_SHIFT) so
that it ends up decrementing from INT_MIN.

Use an unsigned constant '1U' to generate the mask in shift_and_mask().

 References:
https://git.kernel.org/stable/c/90a6a844b2d9927d192758438a4ada33d8cd9de5
https://git.kernel.org/stable/c/38f7e14519d39cf524ddc02d4caee9b337dad703
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