[PATCH] ext4: Fix buffer_head refcnt leak when ext4_iget() fails

[PATCH] ext4: Fix buffer_head refcnt leak when ext4_iget() fails

[Xiyu Yang]

ext4_orphan_get() invokes ext4_read_inode_bitmap(), which returns a
reference of the specified buffer_head object to "bitmap_bh" with
increased refcnt.

When ext4_orphan_get() returns, local variable "bitmap_bh" becomes
invalid, so the refcount should be decreased to keep refcount balanced.

The reference counting issue happens in one exception handling path of
ext4_orphan_get(). When ext4_iget() fails, the function forgets to
decrease the refcnt increased by ext4_read_inode_bitmap(), causing a
refcnt leak.

Fix this issue by calling brelse() when ext4_iget() fails.

Signed-off-by: Xiyu Yang <xiyuyang19@fudan.edu.cn>
Signed-off-by: Xin Tan <tanxin.ctf@gmail.com>
---
 fs/ext4/ialloc.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/fs/ext4/ialloc.c b/fs/ext4/ialloc.c
index f95ee99091e4..2e4729ba17e6 100644
--- a/fs/ext4/ialloc.c
+++ b/fs/ext4/ialloc.c
@@ -1234,6 +1234,7 @@ struct inode *ext4_orphan_get(struct super_block *sb, unsigned long ino)
 		ext4_set_errno(sb, -err);
 		ext4_error(sb, "couldn't read orphan inode %lu (err %d)",
 			   ino, err);
+		brelse(bitmap_bh);
 		return inode;
 	}
 
-- 
2.7.4

Re: [PATCH] ext4: Fix buffer_head refcnt leak when ext4_iget() fails

[Theodore Y. Ts'o]

On Thu, Apr 23, 2020 at 01:09:27PM +0800, Xiyu Yang wrote:
> ext4_orphan_get() invokes ext4_read_inode_bitmap(), which returns a
> reference of the specified buffer_head object to "bitmap_bh" with
> increased refcnt.
> 
> When ext4_orphan_get() returns, local variable "bitmap_bh" becomes
> invalid, so the refcount should be decreased to keep refcount balanced.
> 
> The reference counting issue happens in one exception handling path of
> ext4_orphan_get(). When ext4_iget() fails, the function forgets to
> decrease the refcnt increased by ext4_read_inode_bitmap(), causing a
> refcnt leak.
> 
> Fix this issue by calling brelse() when ext4_iget() fails.
> 
> Signed-off-by: Xiyu Yang <xiyuyang19@fudan.edu.cn>
> Signed-off-by: Xin Tan <tanxin.ctf@gmail.com>

Applied, thanks.

					- Ted