From: Qu Wenruo wqu@suse.com
commit 57949d033a09c57d77be218b5bec07af6878ab32 upstream.
[BUG] When mounting a fs with reloc tree and has qgroup enabled, it can cause NULL pointer dereference at mount time:
BUG: kernel NULL pointer dereference, address: 00000000000000a8 #PF: supervisor read access in kernel mode #PF: error_code(0x0000) - not-present page PGD 0 P4D 0 Oops: 0000 [#1] PREEMPT SMP NOPTI RIP: 0010:btrfs_qgroup_add_swapped_blocks+0x186/0x300 [btrfs] Call Trace: replace_path.isra.23+0x685/0x900 [btrfs] merge_reloc_root+0x26e/0x5f0 [btrfs] merge_reloc_roots+0x10a/0x1a0 [btrfs] btrfs_recover_relocation+0x3cd/0x420 [btrfs] open_ctree+0x1bc8/0x1ed0 [btrfs] btrfs_mount_root+0x544/0x680 [btrfs] legacy_get_tree+0x34/0x60 vfs_get_tree+0x2d/0xf0 fc_mount+0x12/0x40 vfs_kern_mount.part.12+0x61/0xa0 vfs_kern_mount+0x13/0x20 btrfs_mount+0x16f/0x860 [btrfs] legacy_get_tree+0x34/0x60 vfs_get_tree+0x2d/0xf0 do_mount+0x81f/0xac0 ksys_mount+0xbf/0xe0 __x64_sys_mount+0x25/0x30 do_syscall_64+0x65/0x240 entry_SYSCALL_64_after_hwframe+0x49/0xbe
[CAUSE] In btrfs_recover_relocation(), we don't have enough info to determine which block group we're relocating, but only to merge existing reloc trees.
Thus in btrfs_recover_relocation(), rc->block_group is NULL. btrfs_qgroup_add_swapped_blocks() hasn't taken this into consideration, and causes a NULL pointer dereference.
The bug is introduced by commit 3d0174f78e72 ("btrfs: qgroup: Only trace data extents in leaves if we're relocating data block group"), and later qgroup refactoring still keeps this optimization.
[FIX] Thankfully in the context of btrfs_recover_relocation(), there is no other progress can modify tree blocks, thus those swapped tree blocks pair will never affect qgroup numbers, no matter whatever we set for block->trace_leaf.
So we only need to check if @bg is NULL before accessing @bg->flags.
Reported-by: Juan Erbes jerbes@gmail.com Link: https://bugzilla.opensuse.org/show_bug.cgi?id=1134806 Fixes: 3d0174f78e72 ("btrfs: qgroup: Only trace data extents in leaves if we're relocating data block group") CC: stable@vger.kernel.org # 4.20+ Signed-off-by: Qu Wenruo wqu@suse.com Signed-off-by: David Sterba dsterba@suse.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- fs/btrfs/qgroup.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-)
--- a/fs/btrfs/qgroup.c +++ b/fs/btrfs/qgroup.c @@ -3831,7 +3831,13 @@ int btrfs_qgroup_add_swapped_blocks(stru subvol_slot); block->last_snapshot = last_snapshot; block->level = level; - if (bg->flags & BTRFS_BLOCK_GROUP_DATA) + + /* + * If we have bg == NULL, we're called from btrfs_recover_relocation(), + * no one else can modify tree blocks thus we qgroup will not change + * no matter the value of trace_leaf. + */ + if (bg && bg->flags & BTRFS_BLOCK_GROUP_DATA) block->trace_leaf = true; else block->trace_leaf = false;