From: Filipe Manana fdmanana@suse.com
[ Upstream commit 2d892ccdc163a3d2e08c5ed1cea8b61bf7e4f531 ]
When trying to get a new fs root for a snapshot during the transaction at transaction.c:create_pending_snapshot(), if btrfs_get_new_fs_root() fails we leave "pending->snap" pointing to an error pointer, and then later at ioctl.c:create_snapshot() we dereference that pointer, resulting in a crash:
[12264.614689] BUG: kernel NULL pointer dereference, address: 00000000000007c4 [12264.615650] #PF: supervisor write access in kernel mode [12264.616487] #PF: error_code(0x0002) - not-present page [12264.617436] PGD 0 P4D 0 [12264.618328] Oops: 0002 [#1] PREEMPT SMP DEBUG_PAGEALLOC PTI [12264.619150] CPU: 0 PID: 2310635 Comm: fsstress Tainted: G W 5.9.0-rc3-btrfs-next-67 #1 [12264.619960] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.13.0-0-gf21b5a4aeb02-prebuilt.qemu.org 04/01/2014 [12264.621769] RIP: 0010:btrfs_mksubvol+0x438/0x4a0 [btrfs] [12264.622528] Code: bc ef ff ff (...) [12264.624092] RSP: 0018:ffffaa6fc7277cd8 EFLAGS: 00010282 [12264.624669] RAX: 00000000fffffff4 RBX: ffff9d3e8f151a60 RCX: 0000000000000000 [12264.625249] RDX: 0000000000000001 RSI: ffffffff9d56c9be RDI: fffffffffffffff4 [12264.625830] RBP: ffff9d3e8f151b48 R08: 0000000000000000 R09: 0000000000000000 [12264.626413] R10: 0000000000000000 R11: 0000000000000000 R12: 00000000fffffff4 [12264.626994] R13: ffff9d3ede380538 R14: ffff9d3ede380500 R15: ffff9d3f61b2eeb8 [12264.627582] FS: 00007f140d5d8200(0000) GS:ffff9d3fb5e00000(0000) knlGS:0000000000000000 [12264.628176] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [12264.628773] CR2: 00000000000007c4 CR3: 000000020f8e8004 CR4: 00000000003706f0 [12264.629379] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 [12264.629994] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 [12264.630594] Call Trace: [12264.631227] btrfs_mksnapshot+0x7b/0xb0 [btrfs] [12264.631840] __btrfs_ioctl_snap_create+0x16f/0x1a0 [btrfs] [12264.632458] btrfs_ioctl_snap_create_v2+0xb0/0xf0 [btrfs] [12264.633078] btrfs_ioctl+0x1864/0x3130 [btrfs] [12264.633689] ? do_sys_openat2+0x1a7/0x2d0 [12264.634295] ? kmem_cache_free+0x147/0x3a0 [12264.634899] ? __x64_sys_ioctl+0x83/0xb0 [12264.635488] __x64_sys_ioctl+0x83/0xb0 [12264.636058] do_syscall_64+0x33/0x80 [12264.636616] entry_SYSCALL_64_after_hwframe+0x44/0xa9
(gdb) list *(btrfs_mksubvol+0x438) 0x7c7b8 is in btrfs_mksubvol (fs/btrfs/ioctl.c:858). 853 ret = 0; 854 pending_snapshot->anon_dev = 0; 855 fail: 856 /* Prevent double freeing of anon_dev */ 857 if (ret && pending_snapshot->snap) 858 pending_snapshot->snap->anon_dev = 0; 859 btrfs_put_root(pending_snapshot->snap); 860 btrfs_subvolume_release_metadata(root, &pending_snapshot->block_rsv); 861 free_pending: 862 if (pending_snapshot->anon_dev)
So fix this by setting "pending->snap" to NULL if we get an error from the call to btrfs_get_new_fs_root() at transaction.c:create_pending_snapshot().
Fixes: 2dfb1e43f57dd3 ("btrfs: preallocate anon block device at first phase of snapshot creation") Signed-off-by: Filipe Manana fdmanana@suse.com Reviewed-by: David Sterba dsterba@suse.com Signed-off-by: David Sterba dsterba@suse.com Signed-off-by: Sasha Levin sashal@kernel.org --- fs/btrfs/transaction.c | 1 + 1 file changed, 1 insertion(+)
diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c index 2710f8ddb95fb..b43ebf55b93e1 100644 --- a/fs/btrfs/transaction.c +++ b/fs/btrfs/transaction.c @@ -1636,6 +1636,7 @@ static noinline int create_pending_snapshot(struct btrfs_trans_handle *trans, pending->snap = btrfs_get_new_fs_root(fs_info, objectid, pending->anon_dev); if (IS_ERR(pending->snap)) { ret = PTR_ERR(pending->snap); + pending->snap = NULL; btrfs_abort_transaction(trans, ret); goto fail; }