linux-kernel - [ 14/44] fat: fix possible overflow for fat

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20130605211223.355779383@linuxfoundation.org>
Date:	Wed,  5 Jun 2013 14:12:12 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org,
	Krzysztof Strasburger <strasbur@...w386.ch.pwr.wroc.pl>,
	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [ 14/44] fat: fix possible overflow for fat_clusters

3.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>

commit 7b92d03c3239f43e5b86c9cc9630f026d36ee995 upstream.

Intermediate value of fat_clusters can be overflowed on 32bits arch.

Reported-by: Krzysztof Strasburger <strasbur@...w386.ch.pwr.wroc.pl>
Signed-off-by: OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 fs/fat/inode.c |   15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

--- a/fs/fat/inode.c
+++ b/fs/fat/inode.c
@@ -1237,6 +1237,19 @@ static int fat_read_root(struct inode *i
 	return 0;
 }
 
+static unsigned long calc_fat_clusters(struct super_block *sb)
+{
+	struct msdos_sb_info *sbi = MSDOS_SB(sb);
+
+	/* Divide first to avoid overflow */
+	if (sbi->fat_bits != 12) {
+		unsigned long ent_per_sec = sb->s_blocksize * 8 / sbi->fat_bits;
+		return ent_per_sec * sbi->fat_length;
+	}
+
+	return sbi->fat_length * sb->s_blocksize * 8 / sbi->fat_bits;
+}
+
 /*
  * Read the super block of an MS-DOS FS.
  */
@@ -1433,7 +1446,7 @@ int fat_fill_super(struct super_block *s
 		sbi->fat_bits = (total_clusters > MAX_FAT12) ? 16 : 12;
 
 	/* check that FAT table does not overflow */
-	fat_clusters = sbi->fat_length * sb->s_blocksize * 8 / sbi->fat_bits;
+	fat_clusters = calc_fat_clusters(sb);
 	total_clusters = min(total_clusters, fat_clusters - FAT_START_ENT);
 	if (total_clusters > MAX_FAT(sb)) {
 		if (!silent)


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/