Cryptovec unix error msg: fix clippy & MSRV

cryptovec/src/platform/unix.rs

@@ -5,7 +5,6 @@ use libc::c_void;
 /// Unlock memory on drop for Unix-based systems.
 pub fn munlock(ptr: *const u8, len: usize) {
     unsafe {
-        #[allow(clippy::panic)]
         if libc::munlock(ptr as *const c_void, len) != 0 {
             panic_libc_error("Failed to unlock memory");
         }
@@ -14,7 +13,6 @@ pub fn munlock(ptr: *const u8, len: usize) {
 
 pub fn mlock(ptr: *const u8, len: usize) {
     unsafe {
-        #[allow(clippy::panic)]
         if libc::mlock(ptr as *const c_void, len) != 0 {
             panic_libc_error("Failed to lock memory");
         }
@@ -27,17 +25,25 @@ pub fn memset(ptr: *mut u8, value: i32, size: usize) {
     }
 }
 
+#[allow(clippy::panic)]
 unsafe fn panic_libc_error(msg: &str) {
     let errno = *libc::__errno_location();
     const ERRMAXLEN: usize = 255;
+    const INVALID_ERR: &str = "Unknown";
     let mut errdesc = [0u8; ERRMAXLEN];
     let errdesc = if libc::strerror_r(errno, errdesc.as_mut_ptr() as _, ERRMAXLEN) == 0 {
-        CStr::from_bytes_until_nul(&errdesc)
-            .ok()
-            .and_then(|msg| msg.to_str().ok())
-            .unwrap_or("Invalid error description")
+        if let Some(nul_pos) = errdesc.iter().position(|b| *b == 0) {
+            #[allow(clippy::indexing_slicing)]
+            // safety: the position was just checked, so it is guaranteed to be in range
+            CStr::from_bytes_with_nul(&errdesc[0..nul_pos])
+                .ok()
+                .and_then(|msg| msg.to_str().ok())
+                .unwrap_or(INVALID_ERR)
+        } else {
+            INVALID_ERR
+        }
     } else {
-        "Invalid error"
+        INVALID_ERR
     };
     // Note: if you get 'Cannot allocate memory (0xc)' here,
     // check if your RLIMIT_MEMLOCK (`ulimit -l`) is configured low!