Fix improper pointer provenance

`&mut buffer[0] as *mut u8` will create a raw pointer that is only
allowed to access the very first byte of `buffer`. `slice::as_mut_ptr`
is preferred.

3 files changed, 12 insertions, 7 deletions

diff --git a/talpid-core/src/dns/windows/tcpip.rs b/talpid-core/src/dns/windows/tcpip.rs
index 70bb4660d6..3e0a8ea6e1 100644
--- a/talpid-core/src/dns/windows/tcpip.rs
+++ b/talpid-core/src/dns/windows/tcpip.rs
@@ -164,8 +164,12 @@ fn flush_dns_cache() -> Result<(), Error> {
 /// Obtain a string representation for a GUID object.
 fn string_from_guid(guid: &GUID) -> String {
     let mut buffer = [0u16; 40];
-    let length = unsafe { StringFromGUID2(guid, &mut buffer[0] as *mut _, buffer.len() as i32 - 1) }
-        as usize;
+
+    let length =
+        // SAFETY: `guid` and `buffer` are valid references.
+        // StringFromGUID2 won't write past the end of the provided length.
+        unsafe { StringFromGUID2(guid, buffer.as_mut_ptr(), buffer.len() as i32 - 1) } as usize;
+
     // cannot fail because `buffer` is large enough
     assert!(length > 0);
     let length = length - 1;
diff --git a/talpid-openvpn/src/wintun.rs b/talpid-openvpn/src/wintun.rs
index 21c81e0161..ef5ebd5482 100644
--- a/talpid-openvpn/src/wintun.rs
+++ b/talpid-openvpn/src/wintun.rs
@@ -349,8 +349,11 @@ fn find_adapter_registry_key(find_guid: &str, permissions: REG_SAM_FLAGS) -> io:
 /// Obtain a string representation for a GUID object.
 fn string_from_guid(guid: &GUID) -> String {
     let mut buffer = [0u16; 40];
-    let length = unsafe { StringFromGUID2(guid, &mut buffer[0] as *mut _, buffer.len() as i32 - 1) }
-        as usize;
+
+    // SAFETY: `guid` and `buffer` are valid references.
+    let length =
+        unsafe { StringFromGUID2(guid, buffer.as_mut_ptr(), buffer.len() as i32 - 1) } as usize;
+
     // cannot fail because `buffer` is large enough
     assert!(length > 0);
     let length = length - 1;
diff --git a/talpid-windows/src/net.rs b/talpid-windows/src/net.rs
index a15a2a82db..33c79e1a9d 100644
--- a/talpid-windows/src/net.rs
+++ b/talpid-windows/src/net.rs
@@ -393,9 +393,7 @@ pub fn luid_from_alias<T: AsRef<OsStr>>(alias: T) -> io::Result<NET_LUID_LH> {
 /// Returns the alias of an interface given its LUID.
 pub fn alias_from_luid(luid: &NET_LUID_LH) -> io::Result<OsString> {
     let mut buffer = [0u16; IF_MAX_STRING_SIZE as usize + 1];
-    win32_err!(unsafe {
-        ConvertInterfaceLuidToAlias(luid, &mut buffer[0] as *mut _, buffer.len())
-    })?;
+    win32_err!(unsafe { ConvertInterfaceLuidToAlias(luid, buffer.as_mut_ptr(), buffer.len()) })?;
     let nul = buffer.iter().position(|&c| c == 0u16).unwrap();
     Ok(OsString::from_wide(&buffer[0..nul]))
 }