CVE-2021-47435

In the Linux kernel, the following vulnerability has been resolved: dm: fix
mempool NULL pointer race when completing IO dm_io_dec_pending() calls
end_io_acct() first and will then dec md in-flight pending count. But if a
task is swapping DM table at same time this can result in a crash due to
mempool->elements being NULL: task1 task2 do_resume ->do_suspend
->dm_wait_for_completion bio_endio ->clone_endio ->dm_io_dec_pending
->end_io_acct ->wakeup task1 ->dm_swap_table ->__bind ->__bind_mempools
->bioset_exit ->mempool_exit ->free_io [ 67.330330] Unable to handle kernel
NULL pointer dereference at virtual address 0000000000000000 … [
67.330494] pstate: 80400085 (Nzcv daIf +PAN -UAO) [ 67.330510] pc :
mempool_free+0x70/0xa0 [ 67.330515] lr : mempool_free+0x4c/0xa0 [
67.330520] sp : ffffff8008013b20 [ 67.330524] x29: ffffff8008013b20 x28:
0000000000000004 [ 67.330530] x27: ffffffa8c2ff40a0 x26: 00000000ffff1cc8 [
67.330535] x25: 0000000000000000 x24: ffffffdada34c800 [ 67.330541] x23:
0000000000000000 x22: ffffffdada34c800 [ 67.330547] x21: 00000000ffff1cc8
x20: ffffffd9a1304d80 [ 67.330552] x19: ffffffdada34c970 x18:
000000b312625d9c [ 67.330558] x17: 00000000002dcfbf x16: 00000000000006dd [
67.330563] x15: 000000000093b41e x14: 0000000000000010 [ 67.330569] x13:
0000000000007f7a x12: 0000000034155555 [ 67.330574] x11: 0000000000000001
x10: 0000000000000001 [ 67.330579] x9 : 0000000000000000 x8 :
0000000000000000 [ 67.330585] x7 : 0000000000000000 x6 : ffffff80148b5c1a [
67.330590] x5 : ffffff8008013ae0 x4 : 0000000000000001 [ 67.330596] x3 :
ffffff80080139c8 x2 : ffffff801083bab8 [ 67.330601] x1 : 0000000000000000
x0 : ffffffdada34c970 [ 67.330609] Call trace: [ 67.330616]
mempool_free+0x70/0xa0 [ 67.330627] bio_put+0xf8/0x110 [ 67.330638]
dec_pending+0x13c/0x230 [ 67.330644] clone_endio+0x90/0x180 [ 67.330649]
bio_endio+0x198/0x1b8 [ 67.330655] dec_pending+0x190/0x230 [ 67.330660]
clone_endio+0x90/0x180 [ 67.330665] bio_endio+0x198/0x1b8 [ 67.330673]
blk_update_request+0x214/0x428 [ 67.330683] scsi_end_request+0x2c/0x300 [
67.330688] scsi_io_completion+0xa0/0x710 [ 67.330695]
scsi_finish_command+0xd8/0x110 [ 67.330700] scsi_softirq_done+0x114/0x148 [
67.330708] blk_done_softirq+0x74/0xd0 [ 67.330716] __do_softirq+0x18c/0x374
[ 67.330724] irq_exit+0xb4/0xb8 [ 67.330732] __handle_domain_irq+0x84/0xc0
[ 67.330737] gic_handle_irq+0x148/0x1b0 [ 67.330744] el1_irq+0xe8/0x190 [
67.330753] lpm_cpuidle_enter+0x4f8/0x538 [ 67.330759]
cpuidle_enter_state+0x1fc/0x398 [ 67.330764] cpuidle_enter+0x18/0x20 [
67.330772] do_idle+0x1b4/0x290 [ 67.330778] cpu_startup_entry+0x20/0x28 [
67.330786] secondary_start_kernel+0x160/0x170 Fix this by: 1) Establishing
pointers to ‘struct dm_io’ members in dm_io_dec_pending() so that they may
be passed into end_io_acct() after free_io() is called. 2) Moving
end_io_acct() after free_io().