diff mbox series

[05/13] squashfs: fix divide error in calculate_skip()

Message ID 20210515002716.xFCvUKslt%akpm@linux-foundation.org (mailing list archive)
State New, archived
Headers show
Series [01/13] mm/hugetlb: fix F_SEAL_FUTURE_WRITE | expand

Commit Message

Andrew Morton May 15, 2021, 12:27 a.m. UTC 
From: Phillip Lougher <phillip@squashfs.org.uk>
Subject: squashfs: fix divide error in calculate_skip()

Sysbot has reported a "divide error" which has been identified as being
caused by a corrupted file_size value within the file inode.  This value
has been corrupted to a much larger value than expected.

Calculate_skip() is passed i_size_read(inode) >> msblk->block_log.  Due to
the file_size value corruption this overflows the int argument/variable in
that function, leading to the divide error.

This patch changes the function to use u64.  This will accommodate any
unexpectedly large values due to corruption.

The value returned from calculate_skip() is clamped to be never more than
SQUASHFS_CACHED_BLKS - 1, or 7.  So file_size corruption does not lead to
an unexpectedly large return result here.

Link: https://lkml.kernel.org/r/20210507152618.9447-1-phillip@squashfs.org.uk
Signed-off-by: Phillip Lougher <phillip@squashfs.org.uk>
Reported-by: <syzbot+e8f781243ce16ac2f962@syzkaller.appspotmail.com>
Reported-by: <syzbot+7b98870d4fec9447b951@syzkaller.appspotmail.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 fs/squashfs/file.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)
diff mbox series

Patch

--- a/fs/squashfs/file.c~squashfs-fix-divide-error-in-calculate_skip
+++ a/fs/squashfs/file.c
@@ -211,11 +211,11 @@  failure:
  * If the skip factor is limited in this way then the file will use multiple
  * slots.
  */
-static inline int calculate_skip(int blocks)
+static inline int calculate_skip(u64 blocks)
 {
-	int skip = blocks / ((SQUASHFS_META_ENTRIES + 1)
+	u64 skip = blocks / ((SQUASHFS_META_ENTRIES + 1)
 		 * SQUASHFS_META_INDEXES);
-	return min(SQUASHFS_CACHED_BLKS - 1, skip + 1);
+	return min((u64) SQUASHFS_CACHED_BLKS - 1, skip + 1);
 }