# CVE-2021-47375: linux: In the Linux kernel, the following vulnerability has been resolved:  blktrace: Fix uaf in blk_trace access after remo...

CVE-2021-47375 is fixed in linux on 1 platform, first by DEBIAN-CVE-2021-47375, released May 21, 2024. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2021-47375
- Priority: Routine
- CVSS: 6.2 (medium)
- EPSS: 0.0025
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: May 21, 2024

## Description

In the Linux kernel, the following vulnerability has been resolved:  blktrace: Fix uaf in blk_trace access after removing by sysfs  There is an use-after-free problem triggered by following process:        P1(sda)				P2(sdb) 			echo 0 > /sys/block/sdb/trace/enable 			  blk_trace_remove_queue 			    synchronize_rcu 			    blk_trace_free 			      relay_close rcu_read_lock __blk_add_trace   trace_note_tsk   (Iterate running_trace_list) 			        relay_close_buf 				  relay_destroy_buf 				    kfree(buf)     trace_note(sdb's bt)       relay_reserve         buf->offset <- nullptr deference (use-after-free) !!! rcu_read_unlock  [  502.714379] BUG: kernel NULL pointer dereference, address: 0000000000000010 [  502.715260] #PF: supervisor read access in kernel mode [  502.715903] #PF: error_code(0x0000) - not-present page [  502.716546] PGD 103984067 P4D 103984067 PUD 17592b067 PMD 0 [  502.717252] Oops: 0000 [#1] SMP [  502.720308] RIP: 0010:trace_note.isra.0+0x86/0x360 [  502.732872] Call Trace: [  502.733193]  __blk_add_trace.cold+0x137/0x1a3 [  502.733734]  blk_add_trace_rq+0x7b/0xd0 [  502.734207]  blk_add_trace_rq_issue+0x54/0xa0 [  502.734755]  blk_mq_start_request+0xde/0x1b0 [  502.735287]  scsi_queue_rq+0x528/0x1140 ... [  502.742704]  sg_new_write.isra.0+0x16e/0x3e0 [  502.747501]  sg_ioctl+0x466/0x1100  Reproduce method:   ioctl(/dev/sda, BLKTRACESETUP, blk_user_trace_setup[buf_size=127])   ioctl(/dev/sda, BLKTRACESTART)   ioctl(/dev/sdb, BLKTRACESETUP, blk_user_trace_setup[buf_size=127])   ioctl(/dev/sdb, BLKTRACESTART)    echo 0 > /sys/block/sdb/trace/enable &   // Add delay(mdelay/msleep) before kernel enters blk_trace_free()    ioctl$SG_IO(/dev/sda, SG_IO, ...)   // Enters trace_note_tsk() after blk_trace_free() returned   // Use mdelay in rcu region rather than msleep(which may schedule out)  Remove blk_trace from running_list before calling blk_trace_free() by sysfs if blk_trace is at Blktrace_running state.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | linux Debian 12.15 (bookworm) | 5.14.9-1 | [DEBIAN-CVE-2021-47375](https://patchblox.com/security/data/fix/linux/debian-cve-2021-47375.md) | May 21, 2024 |
| Linux | linux Debian 13.5 (trixie) | 5.14.9-1 | [DEBIAN-CVE-2021-47375](https://patchblox.com/security/data/fix/linux/debian-cve-2021-47375.md) | May 21, 2024 |
| Linux | linux Debian 14 | 5.14.9-1 | [DEBIAN-CVE-2021-47375](https://patchblox.com/security/data/fix/linux/debian-cve-2021-47375.md) | May 21, 2024 |

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