linux-hardening - [PATCH] jfs: Use unsigned variable for length calculations

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Date:   Sat,  4 Feb 2023 10:33:56 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Dave Kleikamp <shaggy@...nel.org>
Cc:     Kees Cook <keescook@...omium.org>,
        Christian Brauner <brauner@...nel.org>,
        Dave Chinner <dchinner@...hat.com>,
        jfs-discussion@...ts.sourceforge.net,
        "Dr. David Alan Gilbert" <linux@...blig.org>,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: [PATCH] jfs: Use unsigned variable for length calculations

To avoid confusing the compiler about possible negative sizes, switch
"ssize" which can never be negative from int to u32.  Seen with GCC 13:

../fs/jfs/namei.c: In function 'jfs_symlink': ../include/linux/fortify-string.h:57:33: warning: '__builtin_memcpy' pointer overflow between offset 0 and size [-2147483648, -1]
[-Warray-bounds=]
   57 | #define __underlying_memcpy     __builtin_memcpy
      |                                 ^
...
../fs/jfs/namei.c:950:17: note: in expansion of macro 'memcpy'
  950 |                 memcpy(ip->i_link, name, ssize);
      |                 ^~~~~~

Cc: Dave Kleikamp <shaggy@...nel.org>
Cc: Christian Brauner <brauner@...nel.org>
Cc: Dave Chinner <dchinner@...hat.com>
Cc: jfs-discussion@...ts.sourceforge.net
Signed-off-by: Kees Cook <keescook@...omium.org>
---
 fs/jfs/namei.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/fs/jfs/namei.c b/fs/jfs/namei.c
index b29d68b5eec5..494b9f4043cf 100644
--- a/fs/jfs/namei.c
+++ b/fs/jfs/namei.c
@@ -876,7 +876,7 @@ static int jfs_symlink(struct mnt_idmap *idmap, struct inode *dip,
 	tid_t tid;
 	ino_t ino = 0;
 	struct component_name dname;
-	int ssize;		/* source pathname size */
+	u32 ssize;		/* source pathname size */
 	struct btstack btstack;
 	struct inode *ip = d_inode(dentry);
 	s64 xlen = 0;
@@ -957,7 +957,7 @@ static int jfs_symlink(struct mnt_idmap *idmap, struct inode *dip,
 		if (ssize > sizeof (JFS_IP(ip)->i_inline))
 			JFS_IP(ip)->mode2 &= ~INLINEEA;
 
-		jfs_info("jfs_symlink: fast symlink added  ssize:%d name:%s ",
+		jfs_info("jfs_symlink: fast symlink added  ssize:%u name:%s ",
 			 ssize, name);
 	}
 	/*
@@ -987,7 +987,7 @@ static int jfs_symlink(struct mnt_idmap *idmap, struct inode *dip,
 		ip->i_size = ssize - 1;
 		while (ssize) {
 			/* This is kind of silly since PATH_MAX == 4K */
-			int copy_size = min(ssize, PSIZE);
+			u32 copy_size = min_t(u32, ssize, PSIZE);
 
 			mp = get_metapage(ip, xaddr, PSIZE, 1);
 
-- 
2.34.1