CVE-2021-47375

Published: 21 May 2024

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.

Status

References

• https://www.cve.org/CVERecord?id=CVE-2021-47375
• https://git.kernel.org/linus/5afedf670caf30a2b5a52da96eb7eac7dee6a9c9 (5.15-rc3)
• https://git.kernel.org/stable/c/488da313edf3abea7f7733efe011c96b23740ab5
• https://git.kernel.org/stable/c/dacfd5e4d1142bfb3809aab3634a375f6f373269
• https://git.kernel.org/stable/c/d56171d9360c0170c5c5f8f7e2362a2e999eca40
• https://git.kernel.org/stable/c/677e362ba807f3aafe6f405c07e0b37244da5222
• https://git.kernel.org/stable/c/ebb8d26d93c3ec3c7576c52a8373a2309423c069
• https://git.kernel.org/stable/c/3815fe7371d2411ce164281cef40d9fc7b323dee
• https://git.kernel.org/stable/c/a5f8e86192612d0183047448d8bbe7918b3f1a26
• https://git.kernel.org/stable/c/5afedf670caf30a2b5a52da96eb7eac7dee6a9c9
• NVD
• Launchpad
• Debian