[PATCH v2 03/10] fs: tweak fsuidgid_has_mapping()

Christian Brauner
2021-11-30T12:11:08Z

If the caller's fs{g,u}id aren't mapped in the mount's idmapping we can
return early and skip the check whether the mapped fs{g,u}id also have a
mapping in the filesystem's idmapping. If the fs{g,u}id aren't mapped in
the mount's idmapping they consequently can't be mapped in the
filesystem's idmapping. So there's no point in checking that.

Link: https://lore.kernel.org/r/20211123114227.3124056-4-brauner@kernel.org (v1)
Cc: Seth Forshee <sforshee@digitalocean.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Al Viro <viro@zeniv.linux.org.uk>
CC: linux-fsdevel@vger.kernel.org
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
---
/* v2 */
unchanged
---
include/linux/fs.h | 14 +++++++++++---
1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/include/linux/fs.h b/include/linux/fs.h
index f5d1ae0a783a..28ab20ce0adc 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1695,10 +1695,18 @@ static inline void inode_fsgid_set(struct inode *inode,
static inline bool fsuidgid_has_mapping(struct super_block *sb,
struct user_namespace *mnt_userns)
{
- struct user_namespace *s_user_ns = sb->s_user_ns;
+ struct user_namespace *fs_userns = sb->s_user_ns;
+ kuid_t kuid;
+ kgid_t kgid;

- return kuid_has_mapping(s_user_ns, mapped_fsuid(mnt_userns)) &&
- kgid_has_mapping(s_user_ns, mapped_fsgid(mnt_userns));
+ kuid = mapped_fsuid(mnt_userns);
+ if (!uid_valid(kuid))
+ return false;
+ kgid = mapped_fsgid(mnt_userns);
+ if (!gid_valid(kgid))
+ return false;
+ return kuid_has_mapping(fs_userns, kuid) &&
+ kgid_has_mapping(fs_userns, kgid);
}

extern struct timespec64 current_time(struct inode *inode);
--
2.30.2