Patch "btrfs: fix signed overflows in btrfs_sync_file" has been added to the 4.2-stable tree

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

    btrfs: fix signed overflows in btrfs_sync_file

to the 4.2-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     btrfs-fix-signed-overflows-in-btrfs_sync_file.patch
and it can be found in the queue-4.2 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From 9dcbeed4d7e11e1dcf5e55475de3754f0855d1c2 Mon Sep 17 00:00:00 2001
From: David Sterba <dsterba@suse.com>
Date: Mon, 9 Nov 2015 11:44:45 +0100
Subject: btrfs: fix signed overflows in btrfs_sync_file

From: David Sterba <dsterba@suse.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@suse.com>
Signed-off-by: Chris Mason <clm@fb.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 fs/btrfs/file.c |   10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -1876,8 +1876,13 @@ int btrfs_sync_file(struct file *file, l
 	struct btrfs_log_ctx ctx;
 	int ret = 0;
 	bool full_sync = 0;
-	const u64 len = end - start + 1;
+	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);
 
 	/*
@@ -2065,8 +2070,7 @@ int btrfs_sync_file(struct file *file, l
 			}
 		}
 		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;


Patches currently in stable-queue which might be from dsterba@suse.com are

queue-4.2/btrfs-check-unsupported-filters-in-balance-arguments.patch
queue-4.2/btrfs-fix-signed-overflows-in-btrfs_sync_file.patch