btrfs: fix use-after-free of cmp workspace pages

btrfs_cmp_data_free() puts cmp's src_pages and dst_pages, but leaves
their page address intact. Now, if you hit "goto again" in
btrfs_extent_same_range() and hit some error in
btrfs_cmp_data_prepare(), you'll try to unlock/put already put pages.

This is simple fix to reset the address to avoid use-after-free.

Fixes: 67b07bd4bec5 ("Btrfs: reuse cmp workspace in EXTENT_SAME ioctl")
Signed-off-by: Naohiro Aota <naota@elisp.net>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index a4d2856..aa914aa 100644 (file)
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -3327,11 +3327,13 @@ static void btrfs_cmp_data_free(struct cmp_pages *cmp)
                if (pg) {
                        unlock_page(pg);
                        put_page(pg);
+                       cmp->src_pages[i] = NULL;
                }
                pg = cmp->dst_pages[i];
                if (pg) {
                        unlock_page(pg);
                        put_page(pg);
+                       cmp->dst_pages[i] = NULL;
                }
        }
 }