[3.16.y-ckt stable] Patch "btrfs: fix signed overflows in btrfs_sync_file" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    btrfs: fix signed overflows in btrfs_sync_file

to the linux-3.16.y-queue branch of the 3.16.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.16.y-queue

This patch is scheduled to be released in version 3.16.7-ckt22.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.16.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From 8b867d859e1c31fd293096f0fddc24fce01ff41b Mon Sep 17 00:00:00 2001
From: David Sterba <dsterba at suse.com>
Date: Mon, 9 Nov 2015 11:44:45 +0100
Subject: btrfs: fix signed overflows in btrfs_sync_file

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 at suse.com>
Signed-off-by: Chris Mason <clm at fb.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 at canonical.com>
Signed-off-by: Luis Henriques <luis.henriques at canonical.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;