Btrfs: fix use-after-free during inode eviction

fdmanana · kdave · commit 421f0922a2cf · 2018-10-19T12:25:33.000+02:00
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 6ca0709 ("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: b9d0b38 ("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>
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
@@ -5268,11 +5268,13 @@ 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);
@@ -5285,7 +5287,7 @@ 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,
