linux-kernel - [PATCH 3.16.y-ckt 124/126] btrfs: fix signed overflows in btrfs_sync

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Message-Id: <1452076655-12851-125-git-send-email-luis.henriques@canonical.com>
Date:	Wed,  6 Jan 2016 10:37:33 +0000
From:	Luis Henriques <luis.henriques@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	David Sterba <dsterba@...e.com>, Chris Mason <clm@...com>,
	Kamal Mostafa <kamal@...onical.com>,
	Luis Henriques <luis.henriques@...onical.com>
Subject: [PATCH 3.16.y-ckt 124/126] btrfs: fix signed overflows in btrfs_sync_file

3.16.7-ckt22 -stable review patch.  If anyone has any objections, please let me know.

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

From: David Sterba <dsterba@...e.com>

commit 9dcbeed4d7e11e1dcf5e55475de3754f0855d1c2 upstream.

The calculation of range length in btrfs_sync_file leads to signed
overflow. This was caught by PaX gcc SIZE_OVERFLOW plugin.

https://forums.grsecurity.net/viewtopic.php?f=1&t=4284

The fsync call passes 0 and LLONG_MAX, the range length does not fit to
loff_t and overflows, but the value is converted to u64 so it silently
works as expected.

The minimal fix is a typecast to u64, switching functions to take
(start, end) instead of (start, len) would be more intrusive.

Coccinelle script found that there's one more opencoded calculation of
the length.

<smpl>
@@
loff_t start, end;
@@
* end - start
</smpl>

Signed-off-by: David Sterba <dsterba@...e.com>
Signed-off-by: Chris Mason <clm@...com>
[ kamal: backport to 3.13-stable: use len in both btrfs_wait_ordered_range
  calls, like
  b659ef0 Btrfs: avoid syncing log in the fast fsync path when not necessary ]
Signed-off-by: Kamal Mostafa <kamal@...onical.com>
Signed-off-by: Luis Henriques <luis.henriques@...onical.com>
---
 fs/btrfs/file.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index 7a71c7885835..8d60cf519578 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -1868,7 +1868,13 @@ int btrfs_sync_file(struct file *file, loff_t start, loff_t end, int datasync)
 	struct btrfs_log_ctx ctx;
 	int ret = 0;
 	bool full_sync = 0;
+	u64 len;
 
+	/*
+	 * The range length can be represented by u64, we have to do the typecasts
+	 * to avoid signed overflow if it's [0, LLONG_MAX] eg. from fsync()
+	 */
+	len = (u64)end - (u64)start + 1;
 	trace_btrfs_sync_file(file, datasync);
 
 	/*
@@ -1896,7 +1902,7 @@ int btrfs_sync_file(struct file *file, loff_t start, loff_t end, int datasync)
 	full_sync = test_bit(BTRFS_INODE_NEEDS_FULL_SYNC,
 			     &BTRFS_I(inode)->runtime_flags);
 	if (full_sync) {
-		ret = btrfs_wait_ordered_range(inode, start, end - start + 1);
+		ret = btrfs_wait_ordered_range(inode, start, len);
 		if (ret) {
 			mutex_unlock(&inode->i_mutex);
 			goto out;
@@ -2001,8 +2007,7 @@ int btrfs_sync_file(struct file *file, loff_t start, loff_t end, int datasync)
 			}
 		}
 		if (!full_sync) {
-			ret = btrfs_wait_ordered_range(inode, start,
-						       end - start + 1);
+			ret = btrfs_wait_ordered_range(inode, start, len);
 			if (ret) {
 				btrfs_end_transaction(trans, root);
 				goto out;
--
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