block-crypto: Fix off-by-one in keypath

  Commit 6ffa1d8 replaced the use
  of strncpy with safe_strncpy.  When we calculate the length here,
  we calculate it up to the separator, but don't include the sep.
  When the string is passed to safe_strncpy, that function subtracts an
  extra 1 byte to make room for the null character, which ends up
  cutting off the last character in the path since the length was
  exact, and relied on the 0-initialized, statically allocated buffer
  to null terminate the string by default.

  This commit increases the length value by one before calling
  safe_strncpy to avoid losing the last byte of data. This essentially
  copies the path, including the separator which was omitted before,
  and then replaces the separator with a null character. It also
  adds MIN() to make sure we don't write outside keydir.

Signed-off-by: Chris Rogers <[email protected]>

drivers/block-crypto.c

@@ -143,8 +143,8 @@ find_keyfile(char **keyfile, const char *dirs,
 			safe_strncpy(keydir, dirs, sizeof(keydir));
 			dirs = NULL;
 		} else {
-			size_t len = sep - dirs;
-			safe_strncpy(keydir, dirs, len);
+			size_t len = (sep - dirs) + 1;
+			safe_strncpy(keydir, dirs, MIN(len, sizeof(keydir)));
 			dirs = sep+1;
 		}