From aecec187d7407c98884187e22814678fbef7e32f Mon Sep 17 00:00:00 2001
From: Dan Gohman <sunfish@mozilla.com>
Date: Tue, 29 Oct 2019 17:11:43 -0700
Subject: [PATCH] Check for overflow when incrementing the `preopen_fd`
 counter. (#157)

If someone somehow defines more preopens than can fit in the
`__wasi_fd_t` index space, we should detect it instead of silently
wrapping around.
---
 src/ctx.rs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/ctx.rs b/src/ctx.rs
index 3f4d9d5cf9..b86bfa2bd7 100644
--- a/src/ctx.rs
+++ b/src/ctx.rs
@@ -135,7 +135,7 @@ impl WasiCtxBuilder {
             let mut fe = FdEntry::from(dir)?;
             fe.preopen_path = Some(guest_path);
             self.fds.insert(preopen_fd, fe);
-            preopen_fd += 1;
+            preopen_fd = preopen_fd.checked_add(1).ok_or(Error::ENFILE)?;
         }
 
         let env = self