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Subject[PATCH 3.12 094/123] btrfs: fix use after free iterating extrefs
Date
From: Chris Mason <clm@fb.com>

3.12-stable review patch. If anyone has any objections, please let me know.

===============

commit dc6c5fb3b514221f2e9d21ee626a9d95d3418dff upstream.

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: Mark Fasheh <mfasheh@suse.de>
Reviewed-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: Mark Fasheh <mfasheh@suse.de>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
---
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 53039de1495d..db6818878462 100644
--- a/fs/btrfs/backref.c
+++ b/fs/btrfs/backref.c
@@ -1668,7 +1668,6 @@ 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;
@@ -1693,9 +1692,8 @@ 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, path->slots[0]);
- ptr = btrfs_item_ptr_offset(leaf, path->slots[0]);
+ item_size = btrfs_item_size_nr(eb, path->slots[0]);
+ ptr = btrfs_item_ptr_offset(eb, path->slots[0]);
cur_offset = 0;

while (cur_offset < item_size) {
@@ -1709,7 +1707,7 @@ 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);
--
2.6.2


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