Re: [PATCH RFC 01/28] ecryptfs: don't leak the inode when a lookup can't open the lower file

[Tyler Hicks <code@tyhicks.com>]

On 2026-10-12 12:20:46, Christian Brauner wrote:
> ecryptfs_lookup_interpose() opens the lower file of a regular file to
> read the size from the header. If that fails it calls make_bad_inode()
> and returns the error. A new inode is still I_NEW at that point and
> nothing ever unlocks or puts it, so it leaks together with the reference
> it holds on the lower inode. And an inode that was already in the cache
> gets marked bad for all its other users instead of just losing the
> reference this lookup took.
> 
> umount then complains:
> 
>   VFS: Busy inodes after unmount of ecryptfs (ecryptfs)
> 
> That's a WARN, or a BUG with CONFIG_BUG_ON_DATA_CORRUPTION. The lower
> filesystem reports the same when it is unmounted. Use iget_failed() for
> a new inode and iput() for one from the cache.
> 
> Reproducer, opening the lower file read-write fails on a read-only bind
> mount:
> 
>   sig=$(printf x | ecryptfs-add-passphrase - | sed -n 's/.*\[\(.*\)\].*/\1/p')
>   mount --bind -o ro /lower /lower
>   mount -i -t ecryptfs -o ecryptfs_sig=$sig,ecryptfs_cipher=aes,ecryptfs_key_bytes=16,ecryptfs_passthrough /lower /upper
>   cat /upper/f      # EROFS
>   umount /upper     # VFS: Busy inodes after unmount of ecryptfs
> 
> Fixes: 3b06b3ebf441 ("eCryptfs: Fix new inode race condition")
> Cc: stable@vger.kernel.org
> Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>

Thanks, Christian! I ran this through the regression tests in the
ecryptfs-utils project and everything passed. I also followed the steps
in your reproducer, with and without this change, and verified that it
fixes the intended issue.

  Acked-by: Tyler Hicks <code@tyhicks.com>

Tyler

> ---
>  fs/ecryptfs/inode.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/ecryptfs/inode.c b/fs/ecryptfs/inode.c
> index 525297c7ebd8..0d8452558a98 100644
> --- a/fs/ecryptfs/inode.c
> +++ b/fs/ecryptfs/inode.c
> @@ -362,7 +362,10 @@ static struct dentry *ecryptfs_lookup_interpose(struct dentry *dentry,
>  	if (S_ISREG(inode->i_mode)) {
>  		rc = ecryptfs_i_size_read(dentry, inode);
>  		if (rc) {
> -			make_bad_inode(inode);
> +			if (inode_state_read_once(inode) & I_NEW)
> +				iget_failed(inode);
> +			else
> +				iput(inode);
>  			return ERR_PTR(rc);
>  		}
>  	}
> 
> -- 
> 2.53.0
> 
>