NTFS: Fix an (innocent) off-by-one error in the runlist code.

Signed-off-by: Anton Altaparmakov <aia21@cantab.net>

1 files changed, 8 insertions, 4 deletions

diff --git a/fs/ntfs/runlist.c b/fs/ntfs/runlist.c
index 061b5ff6b73c..eb52b801512b 100644
--- a/fs/ntfs/runlist.c
+++ b/fs/ntfs/runlist.c
@@ -381,6 +381,7 @@ static inline runlist_element *ntfs_rl_insert(runlist_element *dst,
 static inline runlist_element *ntfs_rl_replace(runlist_element *dst,
                 int dsize, runlist_element *src, int ssize, int loc)
 {
+        signed delta;
         BOOL left = FALSE;      /* Left end of @src needs merging. */
         BOOL right = FALSE;     /* Right end of @src needs merging. */
         int tail;               /* Start of tail of @dst. */
@@ -396,11 +397,14 @@ static inline runlist_element *ntfs_rl_replace(runlist_element *dst,
                 left = ntfs_are_rl_mergeable(dst + loc - 1, src);
         /*
          * Allocate some space.  We will need less if the left, right, or both
-         * ends get merged.
+         * ends get merged.  The -1 accounts for the run being replaced.
          */
-        dst = ntfs_rl_realloc(dst, dsize, dsize + ssize - left - right);
-        if (IS_ERR(dst))
-                return dst;
+        delta = ssize - 1 - left - right;
+        if (delta > 0) {
+                dst = ntfs_rl_realloc(dst, dsize, dsize + delta);
+                if (IS_ERR(dst))
+                        return dst;
+        }
         /*
          * We are guaranteed to succeed from here so can start modifying the
          * original runlists.