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SubjectRe: [PATCH 1/1] xattr: Allow user.* xattr on symlink/special files with CAP_SYS_RESOURCE
On Fri, Jun 25, 2021 at 03:12:29PM -0400, Vivek Goyal wrote:
> As of now user.* xattrs are allowed only on regular files and directories.
> And in case of directories if sticky bit is set, then it is allowed
> only if caller is owner or has CAP_FOWNER.
>
> "man xattr" suggests that primary reason behind this restrcition is that
> users can set unlimited amount of "user.*" xattrs on symlinks and special
> files and bypass quota checks. Following is from man page.
>
> "These differences would allow users to consume filesystem resources in
> a way not controllable by disk quotas for group or world writable spe‐
> cial files and directories"
>
> Capability CAP_SYS_RESOURCE allows for overriding disk quota limits. If
> being able to bypass quota is primary reason behind these restrictions,
> can we relax these restrictions if caller has CAP_SYS_RESOURCE.
>
> Signed-off-by: Vivek Goyal <vgoyal@redhat.com>

Got an email from intel kernel test robot that xfstest generic/062 breaks
due to this change.

I think I will have to fix the test case because test is working with
previous behvior where "user.*" xattr will not be permitted on
non-regular/non-dir file.

Thanks
Vivek

> ---
> fs/xattr.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/fs/xattr.c b/fs/xattr.c
> index 5c8c5175b385..10bb918029dd 100644
> --- a/fs/xattr.c
> +++ b/fs/xattr.c
> @@ -124,7 +124,8 @@ xattr_permission(struct user_namespace *mnt_userns, struct inode *inode,
> * extended attributes. For sticky directories, only the owner and
> * privileged users can write attributes.
> */
> - if (!strncmp(name, XATTR_USER_PREFIX, XATTR_USER_PREFIX_LEN)) {
> + if (!strncmp(name, XATTR_USER_PREFIX, XATTR_USER_PREFIX_LEN) &&
> + !capable(CAP_SYS_RESOURCE)) {
> if (!S_ISREG(inode->i_mode) && !S_ISDIR(inode->i_mode))
> return (mask & MAY_WRITE) ? -EPERM : -ENODATA;
> if (S_ISDIR(inode->i_mode) && (inode->i_mode & S_ISVTX) &&
> --
> 2.25.4
>

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