CVE-2021-47435

In the Linux kernel, the following vulnerability has been resolved:<br /> <br /> dm: fix mempool NULL pointer race when completing IO<br /> <br /> dm_io_dec_pending() calls end_io_acct() first and will then dec md<br /> in-flight pending count. But if a task is swapping DM table at same<br /> time this can result in a crash due to mempool-&gt;elements being NULL:<br /> <br /> task1 task2<br /> do_resume<br /> -&gt;do_suspend<br /> -&gt;dm_wait_for_completion<br /> bio_endio<br /> -&gt;clone_endio<br /> -&gt;dm_io_dec_pending<br /> -&gt;end_io_acct<br /> -&gt;wakeup task1<br /> -&gt;dm_swap_table<br /> -&gt;__bind<br /> -&gt;__bind_mempools<br /> -&gt;bioset_exit<br /> -&gt;mempool_exit<br /> -&gt;free_io<br /> <br /> [ 67.330330] Unable to handle kernel NULL pointer dereference at<br /> virtual address 0000000000000000<br /> ......<br /> [ 67.330494] pstate: 80400085 (Nzcv daIf +PAN -UAO)<br /> [ 67.330510] pc : mempool_free+0x70/0xa0<br /> [ 67.330515] lr : mempool_free+0x4c/0xa0<br /> [ 67.330520] sp : ffffff8008013b20<br /> [ 67.330524] x29: ffffff8008013b20 x28: 0000000000000004<br /> [ 67.330530] x27: ffffffa8c2ff40a0 x26: 00000000ffff1cc8<br /> [ 67.330535] x25: 0000000000000000 x24: ffffffdada34c800<br /> [ 67.330541] x23: 0000000000000000 x22: ffffffdada34c800<br /> [ 67.330547] x21: 00000000ffff1cc8 x20: ffffffd9a1304d80<br /> [ 67.330552] x19: ffffffdada34c970 x18: 000000b312625d9c<br /> [ 67.330558] x17: 00000000002dcfbf x16: 00000000000006dd<br /> [ 67.330563] x15: 000000000093b41e x14: 0000000000000010<br /> [ 67.330569] x13: 0000000000007f7a x12: 0000000034155555<br /> [ 67.330574] x11: 0000000000000001 x10: 0000000000000001<br /> [ 67.330579] x9 : 0000000000000000 x8 : 0000000000000000<br /> [ 67.330585] x7 : 0000000000000000 x6 : ffffff80148b5c1a<br /> [ 67.330590] x5 : ffffff8008013ae0 x4 : 0000000000000001<br /> [ 67.330596] x3 : ffffff80080139c8 x2 : ffffff801083bab8<br /> [ 67.330601] x1 : 0000000000000000 x0 : ffffffdada34c970<br /> [ 67.330609] Call trace:<br /> [ 67.330616] mempool_free+0x70/0xa0<br /> [ 67.330627] bio_put+0xf8/0x110<br /> [ 67.330638] dec_pending+0x13c/0x230<br /> [ 67.330644] clone_endio+0x90/0x180<br /> [ 67.330649] bio_endio+0x198/0x1b8<br /> [ 67.330655] dec_pending+0x190/0x230<br /> [ 67.330660] clone_endio+0x90/0x180<br /> [ 67.330665] bio_endio+0x198/0x1b8<br /> [ 67.330673] blk_update_request+0x214/0x428<br /> [ 67.330683] scsi_end_request+0x2c/0x300<br /> [ 67.330688] scsi_io_completion+0xa0/0x710<br /> [ 67.330695] scsi_finish_command+0xd8/0x110<br /> [ 67.330700] scsi_softirq_done+0x114/0x148<br /> [ 67.330708] blk_done_softirq+0x74/0xd0<br /> [ 67.330716] __do_softirq+0x18c/0x374<br /> [ 67.330724] irq_exit+0xb4/0xb8<br /> [ 67.330732] __handle_domain_irq+0x84/0xc0<br /> [ 67.330737] gic_handle_irq+0x148/0x1b0<br /> [ 67.330744] el1_irq+0xe8/0x190<br /> [ 67.330753] lpm_cpuidle_enter+0x4f8/0x538<br /> [ 67.330759] cpuidle_enter_state+0x1fc/0x398<br /> [ 67.330764] cpuidle_enter+0x18/0x20<br /> [ 67.330772] do_idle+0x1b4/0x290<br /> [ 67.330778] cpu_startup_entry+0x20/0x28<br /> [ 67.330786] secondary_start_kernel+0x160/0x170<br /> <br /> Fix this by:<br /> 1) Establishing pointers to &amp;#39;struct dm_io&amp;#39; members in<br /> dm_io_dec_pending() so that they may be passed into end_io_acct()<br /> _after_ free_io() is called.<br /> 2) Moving end_io_acct() after free_io().