On Fri, Sep 08, 2023 at 05:05:27PM -0400, Jeff Layton wrote:
> In the not too distant past, the VFS ACL infrastructure would return
> -EOPNOTSUPP on filesystems (like NFS) that set SB_POSIXACL but that
> don't supply a get_acl or get_inode_acl method. On more recent kernels
> this returns -ENODATA, which breaks one method of detecting when ACLs
> are supported.
>
> Fix __get_acl to also check whether the inode has a "get_(inode_)?acl"
> method and to just return -EOPNOTSUPP if not.
>
> Reported-by: Ondrej Valousek <ondrej.valousek.xm@xxxxxxxxxxx>
> Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx>
> ---
> This patch is another approach to fixing this issue. I don't care too
> much either way which approach we take, but this may fix the problem
> for other filesystems too. Should we take a belt and suspenders
> approach here and fix it in both places?
> ---
> fs/posix_acl.c | 8 ++++++--
> 1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/fs/posix_acl.c b/fs/posix_acl.c
> index a05fe94970ce..4c7c62040c43 100644
> --- a/fs/posix_acl.c
> +++ b/fs/posix_acl.c
> @@ -130,8 +130,12 @@ static struct posix_acl *__get_acl(struct mnt_idmap *idmap,
> if (!is_uncached_acl(acl))
> return acl;
>
> - if (!IS_POSIXACL(inode))
> - return NULL;
> + /*
> + * NB: checking this after checking for a cached ACL allows tmpfs
> + * (which doesn't specify a get_acl operation) to work properly.
> + */
> + if (!IS_POSIXACL(inode) || (!inode->i_op->get_acl && !inode->i_op->get_inode_acl))
> + return ERR_PTR(-EOPNOTSUPP);
Hmmm, I think that'll cause issues for permission checking during
lookup:
generic_permission()
-> acl_permission_check()
-> check_acl()
-> get_inode_acl()
-> __get_acl()
// return ERR_PTR(-EOPNOTSUPP) instead of NULL
Before this change this would've returned NULL and thus check_acl()
would've returned EAGAIN which would've informed acl_permission_check()
to continue with non-ACL based permission checking.
Now you're going to error out with EOPNOTSUPP and cause permission
checking to fallback to CAP_DAC_READ_SEARCH/CAP_DAC_OVERRIDE.
So if you want this change you'll either need to change check_acl() as well.
Unless I'm misreading.
