Re: [PATCH] fix vfs/utils.c for big-endian systems

["Darrick J. Wong" <djwong@kernel.org>]

On Mon, Jan 27, 2025 at 03:43:24PM -0600, Eric Sandeen wrote:
> generic/633 was failing with EINVAL on the fsxgetattr call on s390.
> Looks like this is due to a failure to properly endian swap the
> arguments to the syscall, so fix that, and the magic_etc compare
> in expected_dummy_vfs_caps_uid() as well while we're at it.

Hmmm, I see this when running the same test on ext4:

--- /tmp/fstests/tests/generic/633.out  2025-01-16 12:11:43.921449208 -0800
+++ /var/tmp/fstests/generic/633.out.bad        2025-01-27 13:49:27.413943989 -0800
@@ -1,2 +1,4 @@
 QA output created by 633
 Silence is golden
+utils.c: 928: openat_tmpfile_supported - Invalid argument - failure: create
+utils.c: 928: openat_tmpfile_supported - Invalid argument - failure: create

I think this is a separate bug?  And curiously it doesn't trigger on xfs
or btrfs :P

> Fixes: 0d1af68e ("generic: add fstests for idmapped mounts")
> Signed-off-by: Eric Sandeen <sandeen@redhat.com>
> ---
> 
> diff --git a/src/vfs/utils.c b/src/vfs/utils.c
> index c1c7951c..52bb7e42 100644
> --- a/src/vfs/utils.c
> +++ b/src/vfs/utils.c
> @@ -650,7 +650,7 @@ bool expected_dummy_vfs_caps_uid(int fd, uid_t expected_uid)
>  	if (ret < 0 || ret == 0)
>  		return false;
>  
> -	if (ns_xattr.magic_etc & VFS_CAP_REVISION_3) {
> +	if (le32_to_cpu(ns_xattr.magic_etc) & VFS_CAP_REVISION_3) {
>  
>  		if (le32_to_cpu(ns_xattr.rootid) != expected_uid) {
>  			errno = EINVAL;
> @@ -673,10 +673,12 @@ int set_dummy_vfs_caps(int fd, int flags, int rootuid)
>  	ns_cap_data.data[(x) >> 5].permitted |= (1 << ((x)&31))
>  
>  	struct vfs_ns_cap_data ns_xattr;
> +	__le32 magic_etc;
>  
>  	memset(&ns_xattr, 0, sizeof(ns_xattr));
>  	__raise_cap_permitted(CAP_NET_RAW, ns_xattr);
> -	ns_xattr.magic_etc |= VFS_CAP_REVISION_3 | VFS_CAP_FLAGS_EFFECTIVE;
> +	magic_etc = (VFS_CAP_REVISION_3 | VFS_CAP_FLAGS_EFFECTIVE);
> +	ns_xattr.magic_etc |= cpu_to_le32(magic_etc);

Not sure why you wouldn't just pass (VFS_CAP_REVISION_3 |
VFS_CAP_FLAGS_EFFECTIVE) directly to cpu_to_le32 but it doesn't matter.

Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>

--D

>  	ns_xattr.rootid = cpu_to_le32(rootuid);
>  
>  	return fsetxattr(fd, "security.capability",
> 
>