[PATCH] fuse: do not allow mapping a non-regular backing file

[PATCH] fuse: do not allow mapping a non-regular backing file

[Amir Goldstein]

We do not support passthrough operations other than read/write on
regular file, so allowing non-regular backing files makes no sense.

Fixes: efad7153bf93 ("fuse: allow O_PATH fd for FUSE_DEV_IOC_BACKING_OPEN")
Cc: <stable@vger.kernel.org>
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
---

Miklos,

While working on readdir passthrough, I realized that we accidentrly
allowed creating backing fds for non-regular files.
This needs to go to stable kernels IMO.

Thanks,
Amir.

 fs/fuse/passthrough.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/fs/fuse/passthrough.c b/fs/fuse/passthrough.c
index 607ef735ad4a..eb97ac009e75 100644
--- a/fs/fuse/passthrough.c
+++ b/fs/fuse/passthrough.c
@@ -237,6 +237,11 @@ int fuse_backing_open(struct fuse_conn *fc, struct fuse_backing_map *map)
 	if (!file)
 		goto out;
 
+	/* read/write/splice/mmap passthrough only relevant for regular files */
+	res = d_is_dir(file->f_path.dentry) ? -EISDIR : -EINVAL;
+	if (!d_is_reg(file->f_path.dentry))
+		goto out_fput;
+
 	backing_sb = file_inode(file)->i_sb;
 	res = -ELOOP;
 	if (backing_sb->s_stack_depth >= fc->max_stack_depth)
-- 
2.43.0

Re: [PATCH] fuse: do not allow mapping a non-regular backing file

[Bernd Schubert]

On 7/10/25 12:08, Amir Goldstein wrote:
> We do not support passthrough operations other than read/write on
> regular file, so allowing non-regular backing files makes no sense.
> 
> Fixes: efad7153bf93 ("fuse: allow O_PATH fd for FUSE_DEV_IOC_BACKING_OPEN")
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Amir Goldstein <amir73il@gmail.com>
> ---
> 
> Miklos,
> 
> While working on readdir passthrough, I realized that we accidentrly
> allowed creating backing fds for non-regular files.
> This needs to go to stable kernels IMO.
> 
> Thanks,
> Amir.
> 
>  fs/fuse/passthrough.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/fs/fuse/passthrough.c b/fs/fuse/passthrough.c
> index 607ef735ad4a..eb97ac009e75 100644
> --- a/fs/fuse/passthrough.c
> +++ b/fs/fuse/passthrough.c
> @@ -237,6 +237,11 @@ int fuse_backing_open(struct fuse_conn *fc, struct fuse_backing_map *map)
>  	if (!file)
>  		goto out;
>  
> +	/* read/write/splice/mmap passthrough only relevant for regular files */
> +	res = d_is_dir(file->f_path.dentry) ? -EISDIR : -EINVAL;
> +	if (!d_is_reg(file->f_path.dentry))
> +		goto out_fput;
> +
>  	backing_sb = file_inode(file)->i_sb;
>  	res = -ELOOP;
>  	if (backing_sb->s_stack_depth >= fc->max_stack_depth)

LGTM,

Reviewed-by: Bernd Schubert <bschubert@ddn.com>