From d6b2faeeb47ea04832dbda39cdf33d2a0dbdfcda Mon Sep 17 00:00:00 2001
From: Jakub Konka <kubkon@jakubkonka.com>
Date: Wed, 1 May 2019 17:05:59 +0200
Subject: [PATCH] Modify fd_prestat to hold C-str together with its length

---
 .../sandboxed-system-primitives/src/posix.c       | 15 +++++++++------
 .../sandboxed-system-primitives/src/posix.h       |  3 ++-
 wasmtime-wasi/src/host_impls.rs                   |  7 +++----
 3 files changed, 14 insertions(+), 11 deletions(-)

diff --git a/wasmtime-wasi/sandboxed-system-primitives/src/posix.c b/wasmtime-wasi/sandboxed-system-primitives/src/posix.c
index 31d379a1b3..95b5846009 100644
--- a/wasmtime-wasi/sandboxed-system-primitives/src/posix.c
+++ b/wasmtime-wasi/sandboxed-system-primitives/src/posix.c
@@ -274,8 +274,10 @@ static bool fd_prestats_grow(
       return false;
 
     // Mark all new file descriptors as unused.
-    for (size_t i = pt->size; i < size; ++i)
-      prestats[i].dir = NULL;
+    for (size_t i = pt->size; i < size; ++i) {
+      prestats[i].dir_name = NULL;
+      prestats[i].dir_name_len = 0;
+    }
     pt->prestats = prestats;
     pt->size = size;
   }
@@ -295,7 +297,8 @@ bool fd_prestats_insert(
     return false;
   }
 
-  pt->prestats[fd].dir = strdup(dir);
+  pt->prestats[fd].dir_name = strdup(dir);
+  pt->prestats[fd].dir_name_len = strlen(dir);
   rwlock_unlock(&pt->lock);
   return true;
 }
@@ -310,7 +313,7 @@ static __wasi_errno_t fd_prestats_get_entry(
   if (fd >= pt->size)
     return __WASI_EBADF;
   struct fd_prestat *prestat = &pt->prestats[fd];
-  if (prestat->dir == NULL)
+  if (prestat->dir_name == NULL)
     return __WASI_EBADF;
 
   *ret = prestat;
@@ -664,12 +667,12 @@ __wasi_errno_t wasmtime_ssp_fd_prestat_dir_name(
     rwlock_unlock(&prestats->lock);
     return error;
   }
-  if (path_len != strlen(prestat->dir)) {
+  if (path_len != prestat->dir_name_len) {
     rwlock_unlock(&prestats->lock);
     return EINVAL;
   }
 
-  memcpy(path, prestat->dir, path_len);
+  memcpy(path, prestat->dir_name, path_len);
 
   rwlock_unlock(&prestats->lock);
 
diff --git a/wasmtime-wasi/sandboxed-system-primitives/src/posix.h b/wasmtime-wasi/sandboxed-system-primitives/src/posix.h
index b3519da78a..6eb7011f7a 100644
--- a/wasmtime-wasi/sandboxed-system-primitives/src/posix.h
+++ b/wasmtime-wasi/sandboxed-system-primitives/src/posix.h
@@ -21,7 +21,8 @@ struct fd_entry;
 struct syscalls;
 
 struct fd_prestat {
-  const char *dir;
+  const char *dir_name;
+  size_t dir_name_len;
 };
 
 struct fd_table {
diff --git a/wasmtime-wasi/src/host_impls.rs b/wasmtime-wasi/src/host_impls.rs
index eb0bae29e0..c73b1e845a 100644
--- a/wasmtime-wasi/src/host_impls.rs
+++ b/wasmtime-wasi/src/host_impls.rs
@@ -98,7 +98,7 @@ fn fd_prestats_get_entry(
     }
 
     let prestat = unsafe { &*pt.prestats.add(fd as usize) };
-    if prestat.dir == ::std::ptr::null() {
+    if prestat.dir_name == ::std::ptr::null() {
         return None;
     }
 
@@ -133,10 +133,9 @@ pub fn wasmtime_ssp_fd_prestat_get(
     rwlock_rdlock!(prestats);
 
     let ret_code = if let Some(prestat) = fd_prestats_get_entry(prestats, fd) {
-        (*buf).pr_type = host::__WASI_PREOPENTYPE_DIR;
+        buf.pr_type = host::__WASI_PREOPENTYPE_DIR;
         unsafe {
-            let dir_name = ::std::ffi::CStr::from_ptr((*prestat).dir).to_str().unwrap();
-            (*buf).u.dir.pr_name_len = dir_name.len();
+            buf.u.dir.pr_name_len = prestat.dir_name_len;
         }
         host::__WASI_ESUCCESS
     } else {