btrfs: fix signed overflows in btrfs_sync_file

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>

CC: stable@vger.kernel.org
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Chris Mason <clm@fb.com>

diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index 3009d4536d389386dba9a582cd84a5da7ff20552..8eb1f3c1b647da1f725906b0b0a19fceab4c4cbc 100644 (file)
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -1882,8 +1882,13 @@ 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;
-       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);
 
        /*
@@ -2071,8 +2076,7 @@ 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;