[PATCH] btrfs: fix use after free iterating extrefs

[PATCH] btrfs: fix use after free iterating extrefs

[Chris Mason]

The code for btrfs inode-resolve has never worked properly for
files with enough hard links to trigger extrefs.  It was trying to
get the leaf out of a path after freeing the path:

	btrfs_release_path(path);
	leaf = path->nodes[0];
	item_size = btrfs_item_size_nr(leaf, slot);

The fix here is to use the extent buffer we cloned just a little higher
up to avoid deadlocks caused by using the leaf in the path.

Signed-off-by: Chris Mason <clm@fb.com>
cc: stable@vger.kernel.org # v3.7+
cc: Mark Fasheh <mfasheh@suse.de>
---
 fs/btrfs/backref.c | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/fs/btrfs/backref.c b/fs/btrfs/backref.c
index ecbc63d..9a2ec79 100644
--- a/fs/btrfs/backref.c
+++ b/fs/btrfs/backref.c
@@ -1828,7 +1828,6 @@ static int iterate_inode_extrefs(u64 inum, struct btrfs_root *fs_root,
 	int found = 0;
 	struct extent_buffer *eb;
 	struct btrfs_inode_extref *extref;
-	struct extent_buffer *leaf;
 	u32 item_size;
 	u32 cur_offset;
 	unsigned long ptr;
@@ -1856,9 +1855,8 @@ static int iterate_inode_extrefs(u64 inum, struct btrfs_root *fs_root,
 		btrfs_set_lock_blocking_rw(eb, BTRFS_READ_LOCK);
 		btrfs_release_path(path);
 
-		leaf = path->nodes[0];
-		item_size = btrfs_item_size_nr(leaf, slot);
-		ptr = btrfs_item_ptr_offset(leaf, slot);
+		item_size = btrfs_item_size_nr(eb, slot);
+		ptr = btrfs_item_ptr_offset(eb, slot);
 		cur_offset = 0;
 
 		while (cur_offset < item_size) {
@@ -1872,7 +1870,7 @@ static int iterate_inode_extrefs(u64 inum, struct btrfs_root *fs_root,
 			if (ret)
 				break;
 
-			cur_offset += btrfs_inode_extref_name_len(leaf, extref);
+			cur_offset += btrfs_inode_extref_name_len(eb, extref);
 			cur_offset += sizeof(*extref);
 		}
 		btrfs_tree_read_unlock_blocking(eb);
-- 
2.4.6

Re: [PATCH] btrfs: fix use after free iterating extrefs

[Filipe Manana]

On Tue, Oct 13, 2015 at 7:06 PM, Chris Mason <clm@fb.com> wrote:
> The code for btrfs inode-resolve has never worked properly for
> files with enough hard links to trigger extrefs.  It was trying to
> get the leaf out of a path after freeing the path:
>
>         btrfs_release_path(path);
>         leaf = path->nodes[0];
>         item_size = btrfs_item_size_nr(leaf, slot);
>
> The fix here is to use the extent buffer we cloned just a little higher
> up to avoid deadlocks caused by using the leaf in the path.
>
> Signed-off-by: Chris Mason <clm@fb.com>
> cc: stable@vger.kernel.org # v3.7+
> cc: Mark Fasheh <mfasheh@suse.de>
Reviewed-by: Filipe Manana <fdmanana@suse.com>

Looks good to me.
I failed to notice that problem at commit [1]

[1] https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=3fe81ce206f3805e0eb5d886aabbf91064655144

> ---
>  fs/btrfs/backref.c | 8 +++-----
>  1 file changed, 3 insertions(+), 5 deletions(-)
>
> diff --git a/fs/btrfs/backref.c b/fs/btrfs/backref.c
> index ecbc63d..9a2ec79 100644
> --- a/fs/btrfs/backref.c
> +++ b/fs/btrfs/backref.c
> @@ -1828,7 +1828,6 @@ static int iterate_inode_extrefs(u64 inum, struct btrfs_root *fs_root,
>         int found = 0;
>         struct extent_buffer *eb;
>         struct btrfs_inode_extref *extref;
> -       struct extent_buffer *leaf;
>         u32 item_size;
>         u32 cur_offset;
>         unsigned long ptr;
> @@ -1856,9 +1855,8 @@ static int iterate_inode_extrefs(u64 inum, struct btrfs_root *fs_root,
>                 btrfs_set_lock_blocking_rw(eb, BTRFS_READ_LOCK);
>                 btrfs_release_path(path);
>
> -               leaf = path->nodes[0];
> -               item_size = btrfs_item_size_nr(leaf, slot);
> -               ptr = btrfs_item_ptr_offset(leaf, slot);
> +               item_size = btrfs_item_size_nr(eb, slot);
> +               ptr = btrfs_item_ptr_offset(eb, slot);
>                 cur_offset = 0;
>
>                 while (cur_offset < item_size) {
> @@ -1872,7 +1870,7 @@ static int iterate_inode_extrefs(u64 inum, struct btrfs_root *fs_root,
>                         if (ret)
>                                 break;
>
> -                       cur_offset += btrfs_inode_extref_name_len(leaf, extref);
> +                       cur_offset += btrfs_inode_extref_name_len(eb, extref);
>                         cur_offset += sizeof(*extref);
>                 }
>                 btrfs_tree_read_unlock_blocking(eb);
> --
> 2.4.6
>
> --
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-- 
Filipe David Manana,

"Reasonable men adapt themselves to the world.
 Unreasonable men adapt the world to themselves.
 That's why all progress depends on unreasonable men."

Re: [PATCH] btrfs: fix use after free iterating extrefs

[Mark Fasheh]

On Tue, Oct 13, 2015 at 02:06:48PM -0400, Chris Mason wrote:
> The code for btrfs inode-resolve has never worked properly for
> files with enough hard links to trigger extrefs.  It was trying to
> get the leaf out of a path after freeing the path:
> 
> 	btrfs_release_path(path);
> 	leaf = path->nodes[0];
> 	item_size = btrfs_item_size_nr(leaf, slot);
> 
> The fix here is to use the extent buffer we cloned just a little higher
> up to avoid deadlocks caused by using the leaf in the path.
> 
> Signed-off-by: Chris Mason <clm@fb.com>
> cc: stable@vger.kernel.org # v3.7+
> cc: Mark Fasheh <mfasheh@suse.de>
Reviewed-by: Mark Fasheh <mfasheh@suse.de>

Thanks for the CC Chris.
	--Mark

--
Mark Fasheh

Re: [PATCH] btrfs: fix use after free iterating extrefs

[Chris Mason]

On Tue, Oct 13, 2015 at 12:17:55PM -0700, Mark Fasheh wrote:
> On Tue, Oct 13, 2015 at 02:06:48PM -0400, Chris Mason wrote:
> > The code for btrfs inode-resolve has never worked properly for
> > files with enough hard links to trigger extrefs.  It was trying to
> > get the leaf out of a path after freeing the path:
> > 
> > 	btrfs_release_path(path);
> > 	leaf = path->nodes[0];
> > 	item_size = btrfs_item_size_nr(leaf, slot);
> > 
> > The fix here is to use the extent buffer we cloned just a little higher
> > up to avoid deadlocks caused by using the leaf in the path.
> > 
> > Signed-off-by: Chris Mason <clm@fb.com>
> > cc: stable@vger.kernel.org # v3.7+
> > cc: Mark Fasheh <mfasheh@suse.de>
> Reviewed-by: Mark Fasheh <mfasheh@suse.de>

Thanks Mark and Filipe, I've tested this and queued it up.

-chris