If alloc_unr() call in the pipe_create() failed, then pipe->pipe_ino is

-1. But, because ino_t is unsigned, this case was not covered by the
test ino > 0 in pipeclose(), leading to the free_unr(-1). Fix it by
explicitely comparing with 0 and -1. [1]

Do no access freed memory, the inode number was cached to prevent access
to cpipe after it possibly was freed, but I failed to commit the right
patch.

Noted by:	gianni [1]
Pointy hat to:	kib
MFC after:	3 days

sys/kern/sys_pipe.c

@@ -1554,8 +1554,8 @@ pipeclose(cpipe)
 	} else
 		PIPE_UNLOCK(cpipe);
 
-	if (ino > 0)
-		free_unr(pipeino_unr, cpipe->pipe_ino);
+	if (ino != 0 && ino != (ino_t)-1)
+		free_unr(pipeino_unr, ino);
 }
 
 /*ARGSUSED*/