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CVE-2021-47375
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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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