Messages in this thread | | | Date | Fri, 26 Apr 2024 19:34:45 +0200 | From | Michal Koutný <> | Subject | Re: CVE-2023-52630: blk-iocost: Fix an UBSAN shift-out-of-bounds warning |
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On Tue, Apr 02, 2024 at 08:22:20AM +0200, Greg Kroah-Hartman <gregkh@linuxfoundation.org> wrote: > Description > =========== > > 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: > <TASK> > 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.
The worst implication is unfair or slowed IO but that can't be quantified given empirical implementation 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.
This means the user has limited control (with noise) over such placements.
> Let's bail early from iocg_kick_delay() in such cases. > > The Linux kernel CVE team has assigned CVE-2023-52630 to this issue.
Based on the above I don't think this fix deserves CVE tracking. Shall it be rejected?
Michal [unhandled content-type:application/pgp-signature] | |