On Thu, 2023-12-28 at 15:15 -0500, trondmy@xxxxxxxxxx wrote:
> From: Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx>
>
> The fallback implementation for the get_name export operation uses
> readdir() to try to match the inode number to a filename. That filename
> is then used together with lookup_one() to produce a dentry.
> A problem arises when we match the '.' or '..' entries, since that
> causes lookup_one() to fail. This has sometimes been seen to occur for
> filesystems that violate POSIX requirements around uniqueness of inode
> numbers, something that is common for snapshot directories.
>
> This patch just ensures that we skip '.' and '..' rather than allowing a
> match.
>
> Fixes: 21d8a15ac333 ("lookup_one_len: don't accept . and ..")
> Signed-off-by: Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx>
> ---
> fs/exportfs/expfs.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/fs/exportfs/expfs.c b/fs/exportfs/expfs.c
> index 3ae0154c5680..84af58eaf2ca 100644
> --- a/fs/exportfs/expfs.c
> +++ b/fs/exportfs/expfs.c
> @@ -255,7 +255,9 @@ static bool filldir_one(struct dir_context *ctx, const char *name, int len,
> container_of(ctx, struct getdents_callback, ctx);
>
> buf->sequence++;
> - if (buf->ino == ino && len <= NAME_MAX) {
> + /* Ignore the '.' and '..' entries */
> + if ((len > 2 || name[0] != '.' || (len == 2 && name[1] != '.')) &&
> + buf->ino == ino && len <= NAME_MAX) {
> memcpy(buf->name, name, len);
> buf->name[len] = '\0';
> buf->found = 1;
Reviewed-by: Jeff Layton <jlayton@xxxxxxxxxx>
