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 3009d45..8eb1f3c 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -1882,8 +1882,13 @@
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 @@
}
}
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;