[PATCH] ext4: free the new extent block when getting its buffer fails

[Alan <3164729207@qq.com>]

ext4_ext_grow_indepth() allocates and accounts a metadata block before
calling sb_getblk_gfp(). If the buffer allocation fails, the new block
has not been linked into the extent tree, but the error path returns
without freeing it. This leaks the block and leaves i_blocks larger
than the number of blocks reachable from the inode.

Commit 8a83ac54940d ("ext4: call bdev_getblk() from sb_getblk_gfp()")
removed the implicit __GFP_NOFAIL from this allocation, making this
error path reachable.

Free the new metadata block before returning -ENOMEM. Use
ext4_free_blocks() to undo both the allocation and inode accounting.

Tested on Linux 6.12.1 by injecting a NULL result at the caller's buffer
acquisition boundary. Before the fix, seven failed extent tree growth
operations left seven allocated but unreachable blocks and i_blocks of
40 instead of 32 on a filesystem with 4 KiB blocks. After the fix, the
same failures leave i_blocks at 32, and e2fsck -fn passes after a normal
unmount. Retrying the operation, truncating the file, and growing the
tree without injection also succeed.

Fixes: 8a83ac54940d ("ext4: call bdev_getblk() from sb_getblk_gfp()")
Cc: stable@vger.kernel.org
Signed-off-by: Alan <3164729207@qq.com>
---
 fs/ext4/extents.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index ad0d80e33f6090..7358df54bcd4ae 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -1333,8 +1333,12 @@ static int ext4_ext_grow_indepth(handle_t *handle, struct inode *inode,
 		return err;
 
 	bh = sb_getblk_gfp(inode->i_sb, newblock, __GFP_MOVABLE | GFP_NOFS);
-	if (unlikely(!bh))
+	if (unlikely(!bh)) {
+		/* The new block has not been linked into the extent tree yet. */
+		ext4_free_blocks(handle, inode, NULL, newblock, 1,
+				 EXT4_FREE_BLOCKS_METADATA);
 		return -ENOMEM;
+	}
 	lock_buffer(bh);
 
 	err = ext4_journal_get_create_access(handle, inode->i_sb, bh,

base-commit: d135ab453a7400a34930bdda1ef4bdc8acfac80e
-- 
2.53.0