Btrfs: fix use-after-free during inode eviction

commit 421f0922a2cfb0c75acd9746454aaa576c711a65 upstream.

At inode.c:evict_inode_truncate_pages(), when we iterate over the
inode's extent states, we access an extent state record's "state" field
after we unlocked the inode's io tree lock. This can lead to a
use-after-free issue because after we unlock the io tree that extent
state record might have been freed due to being merged into another
adjacent extent state record (a previous inflight bio for a read
operation finished in the meanwhile which unlocked a range in the io
tree and cause a merge of extent state records, as explained in the
comment before the while loop added in commit 6ca0709756710 ("Btrfs: fix
hang during inode eviction due to concurrent readahead")).

Fix this by keeping a copy of the extent state's flags in a local
variable and using it after unlocking the io tree.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=201189
Fixes: b9d0b38928e2 ("btrfs: Add handler for invalidate page")
CC: stable@vger.kernel.org # 4.4+
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Filipe Manana <fdmanana@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>

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 50cd0118bcd2aae11c89f319b88263ab38b4f412..dc0f9d089b1931ad669d3df2a08a1cdc7b36318a 100644 (file)
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -5302,11 +5302,13 @@ static void evict_inode_truncate_pages(struct inode *inode)
                struct extent_state *cached_state = NULL;
                u64 start;
                u64 end;
+               unsigned state_flags;
 
                node = rb_first(&io_tree->state);
                state = rb_entry(node, struct extent_state, rb_node);
                start = state->start;
                end = state->end;
+               state_flags = state->state;
                spin_unlock(&io_tree->lock);
 
                lock_extent_bits(io_tree, start, end, &cached_state);
@@ -5319,7 +5321,7 @@ static void evict_inode_truncate_pages(struct inode *inode)
                 *
                 * Note, end is the bytenr of last byte, so we need + 1 here.
                 */
-               if (state->state & EXTENT_DELALLOC)
+               if (state_flags & EXTENT_DELALLOC)
                        btrfs_qgroup_free_data(inode, NULL, start, end - start + 1);
 
                clear_extent_bit(io_tree, start, end,