[PATCH 4.14 197/222] btrfs: Handle owner mismatch gracefully when walking up tree

Greg Kroah-Hartman
2018-11-11T22:51:45Z

From: Qu Wenruo <wqu@suse.com>

commit 65c6e82becec33731f48786e5a30f98662c86b16 upstream.

[BUG]
When mounting certain crafted image, btrfs will trigger kernel BUG_ON()
when trying to recover balance:

kernel BUG at fs/btrfs/extent-tree.c:8956!
invalid opcode: 0000 [#1] PREEMPT SMP NOPTI
CPU: 1 PID: 662 Comm: mount Not tainted 4.18.0-rc1-custom+ #10
RIP: 0010:walk_up_proc+0x336/0x480 [btrfs]
RSP: 0018:ffffb53540c9b890 EFLAGS: 00010202
Call Trace:
walk_up_tree+0x172/0x1f0 [btrfs]
btrfs_drop_snapshot+0x3a4/0x830 [btrfs]
merge_reloc_roots+0xe1/0x1d0 [btrfs]
btrfs_recover_relocation+0x3ea/0x420 [btrfs]
open_ctree+0x1af3/0x1dd0 [btrfs]
btrfs_mount_root+0x66b/0x740 [btrfs]
mount_fs+0x3b/0x16a
vfs_kern_mount.part.9+0x54/0x140
btrfs_mount+0x16d/0x890 [btrfs]
mount_fs+0x3b/0x16a
vfs_kern_mount.part.9+0x54/0x140
do_mount+0x1fd/0xda0
ksys_mount+0xba/0xd0
__x64_sys_mount+0x21/0x30
do_syscall_64+0x60/0x210
entry_SYSCALL_64_after_hwframe+0x49/0xbe

[CAUSE]
Extent tree corruption. In this particular case, reloc tree root's
owner is DATA_RELOC_TREE (should be TREE_RELOC), thus its backref is
corrupted and we failed the owner check in walk_up_tree().

[FIX]
It's pretty hard to take care of every extent tree corruption, but at
least we can remove such BUG_ON() and exit more gracefully.

And since in this particular image, DATA_RELOC_TREE and TREE_RELOC share
the same root (which is obviously invalid), we needs to make
__del_reloc_root() more robust to detect such invalid sharing to avoid
possible NULL dereference as root->node can be NULL in this case.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=200411
Reported-by: Xu Wen <wen.xu@gatech.edu>
CC: stable@vger.kernel.org # 4.4+
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
fs/btrfs/extent-tree.c | 18 ++++++++++++------
fs/btrfs/relocation.c | 2 +-
2 files changed, 13 insertions(+), 7 deletions(-)

--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -9028,15 +9028,14 @@ static noinline int walk_up_proc(struct
if (eb == root->node) {
if (wc->flags[level] & BTRFS_BLOCK_FLAG_FULL_BACKREF)
parent = eb->start;
- else
- BUG_ON(root->root_key.objectid !=
- btrfs_header_owner(eb));
+ else if (root->root_key.objectid != btrfs_header_owner(eb))
+ goto owner_mismatch;
} else {
if (wc->flags[level + 1] & BTRFS_BLOCK_FLAG_FULL_BACKREF)
parent = path->nodes[level + 1]->start;
- else
- BUG_ON(root->root_key.objectid !=
- btrfs_header_owner(path->nodes[level + 1]));
+ else if (root->root_key.objectid !=
+ btrfs_header_owner(path->nodes[level + 1]))
+ goto owner_mismatch;
}

btrfs_free_tree_block(trans, root, eb, parent, wc->refs[level] == 1);
@@ -9044,6 +9043,11 @@ out:
wc->refs[level] = 0;
wc->flags[level] = 0;
return 0;
+
+owner_mismatch:
+ btrfs_err_rl(fs_info, "unexpected tree owner, have %llu expect %llu",
+ btrfs_header_owner(eb), root->root_key.objectid);
+ return -EUCLEAN;
}

static noinline int walk_down_tree(struct btrfs_trans_handle *trans,
@@ -9097,6 +9101,8 @@ static noinline int walk_up_tree(struct
ret = walk_up_proc(trans, root, path, wc);
if (ret > 0)
return 0;
+ if (ret < 0)
+ return ret;

if (path->locks[level]) {
btrfs_tree_unlock_rw(path->nodes[level],
--- a/fs/btrfs/relocation.c
+++ b/fs/btrfs/relocation.c
@@ -1334,7 +1334,7 @@ static void __del_reloc_root(struct btrf
struct mapping_node *node = NULL;
struct reloc_control *rc = fs_info->reloc_ctl;

- if (rc) {
+ if (rc && root->node) {
spin_lock(&rc->reloc_root_tree.lock);
rb_node = tree_search(&rc->reloc_root_tree.rb_root,
root->node->start);