linux-kernel - [PATCH V3] fs: fix undefined behavior in bit shift for SB

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Date:   Mon, 24 Apr 2023 13:18:35 +0800
From:   Hao Ge <gehao@...inos.cn>
To:     viro@...iv.linux.org.uk, brauner@...nel.org
Cc:     linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        gehao618@....com, Hao Ge <gehao@...inos.cn>
Subject: [PATCH V3] 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.

Fixes: e462ec50cb5f ("VFS: Differentiate mount flags (MS_*) from internal superblock flags")
Signed-off-by: Hao Ge <gehao@...inos.cn>
---

v2: add Fixes for changelog
v3: streamline changelog
---
 include/linux/fs.h | 22 +++++++++++-----------
 1 file changed, 11 insertions(+), 11 deletions(-)

diff --git a/include/linux/fs.h b/include/linux/fs.h
index c85916e9f7db..86ab23a05b61 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1069,19 +1069,19 @@ extern int send_sigurg(struct fown_struct *fown);
 #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_POSIXACL	(1U<<16)	/* VFS does not apply the umask */
+#define SB_INLINECRYPT	(1U<<17)	/* Use blk-crypto for encrypted files */
+#define SB_KERNMOUNT	(1U<<22) /* this is a kern_mount call */
+#define SB_I_VERSION	(1U<<23) /* Update inode I_version field */
+#define SB_LAZYTIME	(1U<<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     (1U<<26)
+#define SB_FORCE	(1U<<27)
+#define SB_NOSEC	(1U<<28)
+#define SB_BORN		(1U<<29)
+#define SB_ACTIVE	(1U<<30)
+#define SB_NOUSER	(1U<<31)
 
 /* These flags relate to encoding and casefolding */
 #define SB_ENC_STRICT_MODE_FL	(1 << 0)
-- 
2.25.1


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