Re: [PATCH 1/1] btrfs: Handle owner mismatch gracefully when walking up tree

[Nikolay Borisov <nborisov@suse.com>]

On  1.08.2018 11:08, Qu Wenruo wrote:
> [BUG]
> When mounting certain crafted image, btrfs will trigger kernel BUG_ON()
> when try to recover balance:
> ------
> ------------[ cut here ]------------
> 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
> ---[ end trace d4344e4deee03435 ]---
> ------
> 
> [CAUSE]
> Another extent tree corruption.
> 
> In this particular case, tree reloc root's owner is
> DATA_RELOC_TREE (should be TREE_RELOC_TREE), 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_TREE
> shares the same root (which is obviously invalid), we needs to make
> __del_reloc_root() more robust to detect such invalid share 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>
> Signed-off-by: Qu Wenruo <wqu@suse.com>
> ---
> As always, the patch is also pushed to my github repo, along with other
> fuzzed images related fixes:
> https://github.com/adam900710/linux/tree/tree_checker_enhance
> (BTW, is it correct to indicate a branch like above?)
> ---
>  fs/btrfs/extent-tree.c | 27 +++++++++++++++++++--------
>  fs/btrfs/relocation.c  |  2 +-
>  2 files changed, 20 insertions(+), 9 deletions(-)
> 
> diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
> index da615ebc072e..5f4ca61348b5 100644
> --- a/fs/btrfs/extent-tree.c
> +++ b/fs/btrfs/extent-tree.c
> @@ -8949,17 +8949,26 @@ static noinline int walk_up_proc(struct btrfs_trans_handle *trans,
>  	}
>  
>  	if (eb == root->node) {
> -		if (wc->flags[level] & BTRFS_BLOCK_FLAG_FULL_BACKREF)
> +		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)) {
> +			btrfs_err_rl(fs_info,
> +			"unexpected tree owner, have %llu expect %llu",
> +				     btrfs_header_owner(eb),
> +				     root->root_key.objectid);
> +			return -EINVAL;

EINVAL or ECLEANUP?

> +		}
>  	} else {
> -		if (wc->flags[level + 1] & BTRFS_BLOCK_FLAG_FULL_BACKREF)
> +		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])) {
> +			btrfs_err_rl(fs_info,
> +			"unexpected tree owner, have %llu expect %llu",
> +				     btrfs_header_owner(eb),
> +				     root->root_key.objectid);
> +			return -EINVAL;
ditto
> +		}
>  	}
>  
>  	btrfs_free_tree_block(trans, root, eb, parent, wc->refs[level] == 1);
> @@ -9020,6 +9029,8 @@ static noinline int walk_up_tree(struct btrfs_trans_handle *trans,
>  			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],
> diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c
> index a2fc0bd83a40..c64051d33d05 100644
> --- a/fs/btrfs/relocation.c
> +++ b/fs/btrfs/relocation.c
> @@ -1321,7 +1321,7 @@ static void __del_reloc_root(struct btrfs_root *root)
>  	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);
>