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CVE-2021-47375

Disclosure Date: May 21, 2024 •
CVE-2021-47375
Add MITRE ATT&CK tactics and techniques that apply to this CVE.

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.

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CVSS V3 Severity and Metrics
Base Score:
None
Impact Score:
Unknown
Exploitability Score:
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Vector:
Unknown
Attack Vector (AV):
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Attack Complexity (AC):
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Privileges Required (PR):
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User Interaction (UI):
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Scope (S):
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Confidentiality (C):
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Integrity (I):
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Availability (A):
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General Information

Offensive Application
Unknown
Utility Class
Unknown
Ports
Unknown
OS
Unknown
Vulnerable Versions
Linux 488da313edf3
Linux not down converted
Prerequisites
Unknown
Discovered By
Unknown
PoC Author
Unknown
Metasploit Module
Unknown
Reporter
Unknown

Vendors

  • Linux

Products

  • Linux
Technical Analysis