GHSA-g922-58r5-qrpv

Описание

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

blk-iocost: Fix an UBSAN shift-out-of-bounds warning

When iocg_kick_delay() is called from a CPU different than the one which set the delay, @now may be in the past of @iocg->delay_at leading to the following warning:

UBSAN: shift-out-of-bounds in block/blk-iocost.c:1359:23 shift exponent 18446744073709 is too large for 64-bit type 'u64' (aka 'unsigned long long') ... Call Trace: dump_stack_lvl+0x79/0xc0 __ubsan_handle_shift_out_of_bounds+0x2ab/0x300 iocg_kick_delay+0x222/0x230 ioc_rqos_merge+0x1d7/0x2c0 __rq_qos_merge+0x2c/0x80 bio_attempt_back_merge+0x83/0x190 blk_attempt_plug_merge+0x101/0x150 blk_mq_submit_bio+0x2b1/0x720 submit_bio_noacct_nocheck+0x320/0x3e0 __swap_writepage+0x2ab/0x9d0

The underflow itself doesn't really affect the behavior in any meaningful way; however, the past timestamp may exaggerate the delay amount calculated later in the code, which shouldn't be a material problem given the nature of the delay mechanism.

If @now is in the past, this CPU is racing another CPU which recently set up the delay and there's nothing this CPU can contribute w.r.t. the delay. Let's bail early from iocg_kick_delay() in such cases.