[PATCH 5.15.y 2/2] btrfs: fix extent map leak in NOCOW direct I/O write

[Sasha Levin <sashal@kernel.org>]

From: Shuangpeng Bai <shuangpeng.kernel@gmail.com>

[ Upstream commit 3f950867c307c5413d628a153ac44915bd117ffd ]

btrfs_dio_iomap_begin() calls btrfs_get_extent(), which returns an
extent map reference that must be dropped on all exit paths.

For direct writes into a NOCOW range, btrfs_get_blocks_direct_write()
keeps using that extent map and asks btrfs_create_dio_extent() to
allocate the ordered extent. If that fails, for example because
btrfs_alloc_ordered_extent() fails, the function returns the error
without dropping the input extent map. The PREALLOC path avoided this by
dropping the input extent map before replacing it with the newly created
one.

Check the error from btrfs_create_dio_extent() before replacing the
map and drop the input extent map on failure.

Fixes: 5f9a8a51d8b9 ("Btrfs: add semaphore to synchronize direct IO writes with fsync")
CC: stable@vger.kernel.org
Reviewed-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Shuangpeng Bai <shuangpeng.kernel@gmail.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
[ relocated the direct-I/O fix from fs/btrfs/direct-io.c to fs/btrfs/inode.c ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/btrfs/inode.c | 18 +++++++++++++-----
 1 file changed, 13 insertions(+), 5 deletions(-)

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index f2778d2b96663..84ea24a8e66cf 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -7954,15 +7954,23 @@ static int btrfs_get_blocks_direct_write(struct extent_map **map,
 					      len, orig_block_len,
 					      ram_bytes, type);
 		btrfs_dec_nocow_writers(fs_info, block_start);
-		if (type == BTRFS_ORDERED_PREALLOC) {
-			btrfs_free_extent_map(em);
-			*map = em = em2;
-		}
-
 		if (IS_ERR(em2)) {
 			ret = PTR_ERR(em2);
+			btrfs_free_extent_map(em);
+			*map = NULL;
 			goto out;
 		}
+
+		/*
+		 * True NOCOW writes don't need to create a new extent map,
+		 * while PREALLOC writes must replace the existing one.
+		 */
+		if (em2) {
+			ASSERT(type == BTRFS_ORDERED_PREALLOC);
+			btrfs_free_extent_map(em);
+			*map = em2;
+			em = em2;
+		}
 	} else {
 		/* Our caller expects us to free the input extent map. */
 		btrfs_free_extent_map(em);
-- 
2.53.0