From 57949d033a09c57d77be218b5bec07af6878ab32 Mon Sep 17 00:00:00 2001 From: Qu Wenruo Date: Tue, 21 May 2019 19:28:08 +0800 Subject: [PATCH] btrfs: qgroup: Check bg while resuming relocation to avoid NULL pointer dereference [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 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 Signed-off-by: David Sterba --- fs/btrfs/qgroup.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c index 2f708f2c4e67..3e6ffbbd8b0a 100644 --- a/fs/btrfs/qgroup.c +++ b/fs/btrfs/qgroup.c @@ -3830,7 +3830,13 @@ int btrfs_qgroup_add_swapped_blocks(struct btrfs_trans_handle *trans, 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;