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    Subject[PATCH 4.1 23/46] btrfs: fix use after free iterating extrefs
    Date
    4.1-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Chris Mason <clm@fb.com>

    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: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    fs/btrfs/backref.c | 8 +++-----
    1 file changed, 3 insertions(+), 5 deletions(-)

    --- a/fs/btrfs/backref.c
    +++ b/fs/btrfs/backref.c
    @@ -1786,7 +1786,6 @@ static int iterate_inode_extrefs(u64 inu
    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;
    @@ -1814,9 +1813,8 @@ static int iterate_inode_extrefs(u64 inu
    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) {
    @@ -1830,7 +1828,7 @@ static int iterate_inode_extrefs(u64 inu
    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);



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