fs: use consistent setgid checks in is_sxid()

Now that we made the VFS setgid checking consistent an inode can't be
marked security irrelevant even if the setgid bit is still set. Make
this function consistent with all other helpers.

Note that enforcing consistent setgid stripping checks for file
modification and mode- and ownership changes will cause the setgid bit
to be lost in more cases than useed to be the case. If an unprivileged
user wrote to a non-executable setgid file that they don't have
privilege over the setgid bit will be dropped. This will lead to
temporary failures in some xfstests until they have been updated.

Reported-by: Miklos Szeredi <miklos@szeredi.hu>
Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>

diff --git a/include/linux/fs.h b/include/linux/fs.h
index b39c5efca180678018ac5d0834f7f908e519274f..0a96f5eeee69817c460376d2b4467a1400ee2229 100644 (file)
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -3527,7 +3527,7 @@ int __init list_bdev_fs_names(char *buf, size_t size);
 
 static inline bool is_sxid(umode_t mode)
 {
-       return (mode & S_ISUID) || ((mode & S_ISGID) && (mode & S_IXGRP));
+       return mode & (S_ISUID | S_ISGID);
 }
 
 static inline int check_sticky(struct user_namespace *mnt_userns,