fs: fix undefined behavior in bit shift for SB_NOUSER

Shifting signed 32-bit value by 31 bits is undefined, so changing
significant bit to unsigned. It was spotted by UBSAN.

So let's just fix this by using the BIT() helper for all SB_* flags.

Fixes: e462ec5 ("VFS: Differentiate mount flags (MS_*) from internal superblock flags")
Signed-off-by: Hao Ge <[email protected]>
Message-Id: <[email protected]>
[[email protected]: use BIT() for all SB_* flags]
Signed-off-by: Christian Brauner <[email protected]>

Author: GeHao01994

include/linux/fs.h

@@ -1076,29 +1076,29 @@ extern int send_sigurg(struct fown_struct *fown);
  * sb->s_flags.  Note that these mirror the equivalent MS_* flags where
  * represented in both.
  */
-#define SB_RDONLY	 1	/* Mount read-only */
-#define SB_NOSUID	 2	/* Ignore suid and sgid bits */
-#define SB_NODEV	 4	/* Disallow access to device special files */
-#define SB_NOEXEC	 8	/* Disallow program execution */
-#define SB_SYNCHRONOUS	16	/* Writes are synced at once */
-#define SB_MANDLOCK	64	/* Allow mandatory locks on an FS */
-#define SB_DIRSYNC	128	/* Directory modifications are synchronous */
-#define SB_NOATIME	1024	/* Do not update access times. */
-#define SB_NODIRATIME	2048	/* Do not update directory access times */
-#define SB_SILENT	32768
-#define SB_POSIXACL	(1<<16)	/* VFS does not apply the umask */
-#define SB_INLINECRYPT	(1<<17)	/* Use blk-crypto for encrypted files */
-#define SB_KERNMOUNT	(1<<22) /* this is a kern_mount call */
-#define SB_I_VERSION	(1<<23) /* Update inode I_version field */
-#define SB_LAZYTIME	(1<<25) /* Update the on-disk [acm]times lazily */
+#define SB_RDONLY       BIT(0)	/* Mount read-only */
+#define SB_NOSUID       BIT(1)	/* Ignore suid and sgid bits */
+#define SB_NODEV        BIT(2)	/* Disallow access to device special files */
+#define SB_NOEXEC       BIT(3)	/* Disallow program execution */
+#define SB_SYNCHRONOUS  BIT(4)	/* Writes are synced at once */
+#define SB_MANDLOCK     BIT(6)	/* Allow mandatory locks on an FS */
+#define SB_DIRSYNC      BIT(7)	/* Directory modifications are synchronous */
+#define SB_NOATIME      BIT(10)	/* Do not update access times. */
+#define SB_NODIRATIME   BIT(11)	/* Do not update directory access times */
+#define SB_SILENT       BIT(15)
+#define SB_POSIXACL     BIT(16)	/* VFS does not apply the umask */
+#define SB_INLINECRYPT  BIT(17)	/* Use blk-crypto for encrypted files */
+#define SB_KERNMOUNT    BIT(22)	/* this is a kern_mount call */
+#define SB_I_VERSION    BIT(23)	/* Update inode I_version field */
+#define SB_LAZYTIME     BIT(25)	/* Update the on-disk [acm]times lazily */
 
 /* These sb flags are internal to the kernel */
-#define SB_SUBMOUNT     (1<<26)
-#define SB_FORCE    	(1<<27)
-#define SB_NOSEC	(1<<28)
-#define SB_BORN		(1<<29)
-#define SB_ACTIVE	(1<<30)
-#define SB_NOUSER	(1<<31)
+#define SB_SUBMOUNT     BIT(26)
+#define SB_FORCE        BIT(27)
+#define SB_NOSEC        BIT(28)
+#define SB_BORN         BIT(29)
+#define SB_ACTIVE       BIT(30)
+#define SB_NOUSER       BIT(31)
 
 /* These flags relate to encoding and casefolding */
 #define SB_ENC_STRICT_MODE_FL	(1 << 0)