From: Jason Andryuk jandryuk@gmail.com
[ Upstream commit f9710c357e5bbf64d7ce45ba0bc75a52222491c1 ]
When a VBD is not fully created and then closed, the kernel can have a NULL pointer dereference:
The reproducer is trivial:
[user@dom0 ~]$ sudo xl block-attach work backend=sys-usb vdev=xvdi target=/dev/sdz [user@dom0 ~]$ xl block-list work Vdev BE handle state evt-ch ring-ref BE-path 51712 0 241 4 -1 -1 /local/domain/0/backend/vbd/241/51712 51728 0 241 4 -1 -1 /local/domain/0/backend/vbd/241/51728 51744 0 241 4 -1 -1 /local/domain/0/backend/vbd/241/51744 51760 0 241 4 -1 -1 /local/domain/0/backend/vbd/241/51760 51840 3 241 3 -1 -1 /local/domain/3/backend/vbd/241/51840 ^ note state, the /dev/sdz doesn't exist in the backend
[user@dom0 ~]$ sudo xl block-detach work xvdi [user@dom0 ~]$ xl block-list work Vdev BE handle state evt-ch ring-ref BE-path work is an invalid domain identifier
And its console has:
BUG: kernel NULL pointer dereference, address: 0000000000000050 PGD 80000000edebb067 P4D 80000000edebb067 PUD edec2067 PMD 0 Oops: 0000 [#1] PREEMPT SMP PTI CPU: 1 PID: 52 Comm: xenwatch Not tainted 5.16.18-2.43.fc32.qubes.x86_64 #1 RIP: 0010:blk_mq_stop_hw_queues+0x5/0x40 Code: 00 48 83 e0 fd 83 c3 01 48 89 85 a8 00 00 00 41 39 5c 24 50 77 c0 5b 5d 41 5c 41 5d c3 c3 0f 1f 80 00 00 00 00 0f 1f 44 00 00 <8b> 47 50 85 c0 74 32 41 54 49 89 fc 55 53 31 db 49 8b 44 24 48 48 RSP: 0018:ffffc90000bcfe98 EFLAGS: 00010293 RAX: ffffffffc0008370 RBX: 0000000000000005 RCX: 0000000000000000 RDX: 0000000000000000 RSI: 0000000000000005 RDI: 0000000000000000 RBP: ffff88800775f000 R08: 0000000000000001 R09: ffff888006e620b8 R10: ffff888006e620b0 R11: f000000000000000 R12: ffff8880bff39000 R13: ffff8880bff39000 R14: 0000000000000000 R15: ffff88800604be00 FS: 0000000000000000(0000) GS:ffff8880f3300000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000000000000050 CR3: 00000000e932e002 CR4: 00000000003706e0 Call Trace: <TASK> blkback_changed+0x95/0x137 [xen_blkfront] ? read_reply+0x160/0x160 xenwatch_thread+0xc0/0x1a0 ? do_wait_intr_irq+0xa0/0xa0 kthread+0x16b/0x190 ? set_kthread_struct+0x40/0x40 ret_from_fork+0x22/0x30 </TASK> Modules linked in: snd_seq_dummy snd_hrtimer snd_seq snd_seq_device snd_timer snd soundcore ipt_REJECT nf_reject_ipv4 xt_state xt_conntrack nft_counter nft_chain_nat xt_MASQUERADE nf_nat nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 nft_compat nf_tables nfnetlink intel_rapl_msr intel_rapl_common crct10dif_pclmul crc32_pclmul crc32c_intel ghash_clmulni_intel xen_netfront pcspkr xen_scsiback target_core_mod xen_netback xen_privcmd xen_gntdev xen_gntalloc xen_blkback xen_evtchn ipmi_devintf ipmi_msghandler fuse bpf_preload ip_tables overlay xen_blkfront CR2: 0000000000000050 ---[ end trace 7bc9597fd06ae89d ]--- RIP: 0010:blk_mq_stop_hw_queues+0x5/0x40 Code: 00 48 83 e0 fd 83 c3 01 48 89 85 a8 00 00 00 41 39 5c 24 50 77 c0 5b 5d 41 5c 41 5d c3 c3 0f 1f 80 00 00 00 00 0f 1f 44 00 00 <8b> 47 50 85 c0 74 32 41 54 49 89 fc 55 53 31 db 49 8b 44 24 48 48 RSP: 0018:ffffc90000bcfe98 EFLAGS: 00010293 RAX: ffffffffc0008370 RBX: 0000000000000005 RCX: 0000000000000000 RDX: 0000000000000000 RSI: 0000000000000005 RDI: 0000000000000000 RBP: ffff88800775f000 R08: 0000000000000001 R09: ffff888006e620b8 R10: ffff888006e620b0 R11: f000000000000000 R12: ffff8880bff39000 R13: ffff8880bff39000 R14: 0000000000000000 R15: ffff88800604be00 FS: 0000000000000000(0000) GS:ffff8880f3300000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000000000000050 CR3: 00000000e932e002 CR4: 00000000003706e0 Kernel panic - not syncing: Fatal exception Kernel Offset: disabled
info->rq and info->gd are only set in blkfront_connect(), which is called for state 4 (XenbusStateConnected). Guard against using NULL variables in blkfront_closing() to avoid the issue.
The rest of blkfront_closing looks okay. If info->nr_rings is 0, then for_each_rinfo won't do anything.
blkfront_remove also needs to check for non-NULL pointers before cleaning up the gendisk and request queue.
Fixes: 05d69d950d9d "xen-blkfront: sanitize the removal state machine" Reported-by: Marek Marczykowski-Górecki marmarek@invisiblethingslab.com Signed-off-by: Jason Andryuk jandryuk@gmail.com Reviewed-by: Juergen Gross jgross@suse.com Link: https://lore.kernel.org/r/20220601195341.28581-1-jandryuk@gmail.com Signed-off-by: Juergen Gross jgross@suse.com Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/block/xen-blkfront.c | 19 ++++++++++++------- 1 file changed, 12 insertions(+), 7 deletions(-)
diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c index 390817cf1221..d7a9bf43fb32 100644 --- a/drivers/block/xen-blkfront.c +++ b/drivers/block/xen-blkfront.c @@ -2140,9 +2140,11 @@ static void blkfront_closing(struct blkfront_info *info) return;
/* No more blkif_request(). */ - blk_mq_stop_hw_queues(info->rq); - blk_mark_disk_dead(info->gd); - set_capacity(info->gd, 0); + if (info->rq && info->gd) { + blk_mq_stop_hw_queues(info->rq); + blk_mark_disk_dead(info->gd); + set_capacity(info->gd, 0); + }
for_each_rinfo(info, rinfo, i) { /* No more gnttab callback work. */ @@ -2478,16 +2480,19 @@ static int blkfront_remove(struct xenbus_device *xbdev)
dev_dbg(&xbdev->dev, "%s removed", xbdev->nodename);
- del_gendisk(info->gd); + if (info->gd) + del_gendisk(info->gd);
mutex_lock(&blkfront_mutex); list_del(&info->info_list); mutex_unlock(&blkfront_mutex);
blkif_free(info, 0); - xlbd_release_minors(info->gd->first_minor, info->gd->minors); - blk_cleanup_disk(info->gd); - blk_mq_free_tag_set(&info->tag_set); + if (info->gd) { + xlbd_release_minors(info->gd->first_minor, info->gd->minors); + blk_cleanup_disk(info->gd); + blk_mq_free_tag_set(&info->tag_set); + }
kfree(info); return 0;