CVE-2025-38063 Information

Jun 19, 2025 cve

Description

In the Linux kernel the following vulnerability has been resolved:

dm: fix unconditional IO throttle caused by REQ_PREFLUSH

When a bio with REQ_PREFLUSH is submitted to dm __send_empty_flush() generates a flush_bio with REQ_OP_WRITE | REQ_PREFLUSH | REQ_SYNC which causes the flush_bio to be throttled by wbt_wait().

An example from v5.4 similar problem also exists in upstream:

crash> bt 2091206
PID: 2091206  TASK: ffff2050df92a300  CPU: 109  COMMAND: \kworker/u260:0\n     0 [ffff800084a2f7f0] __switch_to at ffff80004008aeb8
 1 [ffff800084a2f820] __schedule at ffff800040bfa0c4
 2 [ffff800084a2f880] schedule at ffff800040bfa4b4
 3 [ffff800084a2f8a0] io_schedule at ffff800040bfa9c4
 4 [ffff800084a2f8c0] rq_qos_wait at ffff8000405925bc
 5 [ffff800084a2f940] wbt_wait at ffff8000405bb3a0
 6 [ffff800084a2f9a0] __rq_qos_throttle at ffff800040592254
 7 [ffff800084a2f9c0] blk_mq_make_request at ffff80004057cf38
 8 [ffff800084a2fa60] generic_make_request at ffff800040570138
 9 [ffff800084a2fae0] submit_bio at ffff8000405703b4
10 [ffff800084a2fb50] xlog_write_iclog at ffff800001280834 [xfs]
11 [ffff800084a2fbb0] xlog_sync at ffff800001280c3c [xfs]
12 [ffff800084a2fbf0] xlog_state_release_iclog at ffff800001280df4 [xfs]
13 [ffff800084a2fc10] xlog_write at ffff80000128203c [xfs]
14 [ffff800084a2fcd0] xlog_cil_push at ffff8000012846dc [xfs]
15 [ffff800084a2fda0] xlog_cil_push_work at ffff800001284a2c [xfs]
16 [ffff800084a2fdb0] process_one_work at ffff800040111d08
17 [ffff800084a2fe00] worker_thread at ffff8000401121cc
18 [ffff800084a2fe70] kthread at ffff800040118de4

After commit 2def2845cc33 (s: don’t allow log IO to be throttled) the metadata submitted by xlog_write_iclog() should not be throttled. But due to the existence of the dm layer throttling flush_bio indirectly causes the metadata bio to be throttled.

Fix this by conditionally adding REQ_IDLE to flush_bio.bi_opf which makes wbt_should_throttle() return false to avoid wbt_wait().

Reference

https://git.kernel.org/stable/c/2858cda9a8d95e6deee7e3b0a26adde696a9a4f5 https://git.kernel.org/stable/c/52aa28f7b1708d76e315d78b5ed397932a1a97c3 https://git.kernel.org/stable/c/88f7f56d16f568f19e1a695af34a7f4a6ce537a6 https://git.kernel.org/stable/c/95d08924335f3b6f4ea0b92ebfe4fe0731c502d9 https://git.kernel.org/stable/c/b55a97d1bd4083729a60d19beffe85d4c96680de

CNNVD-202506-2191 (Published: 2025-06-18)

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