[PATCH][SRU][D/E] UBUNTU: SAUCE: fs: Move SB_I_NOSUID to the top of s_iflags

[Seth Forshee]

BugLink: https://bugs.launchpad.net/bugs/1851677

SB_I_NOSUID was added by a sauce patch, and over time it has come
to occpy the same bit in s_iflags as SB_I_USERNS_VISIBLE without
being noticed. overlayfs will set SB_I_NOSUID when any lower
mount is nosuid. When this happens for a user namespace mount,
mount_too_revealing() will perform additional, unnecessary checks
which may block mounting when it should be allowed.

Move SB_I_NOSUID to prevent this conflict, and move it to the top
of s_iflags to make future conflicts less likely.

Reported-by: Jann Horn <jannh at google.com>
Signed-off-by: Seth Forshee <seth.forshee at canonical.com>
---
 include/linux/fs.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 25bdf254d5c9..ff2767d66c31 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1380,12 +1380,12 @@ extern int send_sigurg(struct fown_struct *fown);
 #define SB_I_NOEXEC	0x00000002	/* Ignore executables on this fs */
 #define SB_I_NODEV	0x00000004	/* Ignore devices on this fs */
 #define SB_I_MULTIROOT	0x00000008	/* Multiple roots to the dentry tree */
-#define SB_I_NOSUID	0x00000010	/* Ignore suid on this fs */
 
 /* sb->s_iflags to limit user namespace mounts */
 #define SB_I_USERNS_VISIBLE		0x00000010 /* fstype already mounted */
 #define SB_I_IMA_UNVERIFIABLE_SIGNATURE	0x00000020
 #define SB_I_UNTRUSTED_MOUNTER		0x00000040
+#define SB_I_NOSUID			0x80000000 /* Ignore suid on this fs */
 
 /* Possible states of 'frozen' field */
 enum {
-- 
2.20.1