Don't crash when nullptr paired with len = 0

native/src/base/files.rs

@@ -7,10 +7,11 @@ use crate::{bfmt_cstr, errno, xopen};
 
 mod unsafe_impl {
     use std::ffi::CStr;
-    use std::slice;
 
     use libc::c_char;
 
+    use crate::slice_from_ptr_mut;
+
     #[no_mangle]
     pub unsafe extern "C" fn read_link(path: *const c_char, buf: *mut u8, bufsz: usize) -> isize {
         let r = libc::readlink(path, buf.cast(), bufsz - 1);
@@ -22,7 +23,7 @@ mod unsafe_impl {
 
     #[no_mangle]
     unsafe extern "C" fn canonical_path(path: *const c_char, buf: *mut u8, bufsz: usize) -> isize {
-        super::canonical_path(CStr::from_ptr(path), slice::from_raw_parts_mut(buf, bufsz))
+        super::canonical_path(CStr::from_ptr(path), slice_from_ptr_mut(buf, bufsz))
     }
 }
 

native/src/base/misc.rs

@@ -1,7 +1,7 @@
 use std::cmp::min;
 use std::ffi::CStr;
-use std::fmt;
 use std::fmt::Arguments;
+use std::{fmt, slice};
 
 struct BufFmtWriter<'a> {
     buf: &'a mut [u8],
@@ -118,3 +118,23 @@ pub fn errno() -> &'static mut i32 {
 pub fn error_str() -> &'static str {
     unsafe { ptr_to_str(libc::strerror(*errno())) }
 }
+
+// When len is 0, don't care whether buf is null or not
+#[inline]
+pub unsafe fn slice_from_ptr<'a, T>(buf: *const T, len: usize) -> &'a [T] {
+    if len == 0 {
+        &[]
+    } else {
+        slice::from_raw_parts(buf, len)
+    }
+}
+
+// When len is 0, don't care whether buf is null or not
+#[inline]
+pub unsafe fn slice_from_ptr_mut<'a, T>(buf: *mut T, len: usize) -> &'a mut [T] {
+    if len == 0 {
+        &mut []
+    } else {
+        slice::from_raw_parts_mut(buf, len)
+    }
+}

native/src/base/xwrap.rs

@@ -12,36 +12,35 @@ use crate::{canonical_path, cstr, errno, error, mkdirs, perror, ptr_to_str, read
 mod unsafe_impl {
     use std::ffi::CStr;
     use std::os::unix::io::RawFd;
-    use std::slice;
 
     use cfg_if::cfg_if;
     use libc::{c_char, nfds_t, off_t, pollfd};
 
-    use crate::{perror, ptr_to_str};
+    use crate::{perror, ptr_to_str, slice_from_ptr, slice_from_ptr_mut};
 
     #[no_mangle]
     unsafe extern "C" fn xwrite(fd: RawFd, buf: *const u8, bufsz: usize) -> isize {
-        super::xwrite(fd, slice::from_raw_parts(buf, bufsz))
+        super::xwrite(fd, slice_from_ptr(buf, bufsz))
     }
 
     #[no_mangle]
     unsafe extern "C" fn xread(fd: RawFd, buf: *mut u8, bufsz: usize) -> isize {
-        super::xread(fd, slice::from_raw_parts_mut(buf, bufsz))
+        super::xread(fd, slice_from_ptr_mut(buf, bufsz))
     }
 
     #[no_mangle]
     unsafe extern "C" fn xxread(fd: RawFd, buf: *mut u8, bufsz: usize) -> isize {
-        super::xxread(fd, slice::from_raw_parts_mut(buf, bufsz))
+        super::xxread(fd, slice_from_ptr_mut(buf, bufsz))
     }
 
     #[no_mangle]
     unsafe extern "C" fn xcanonical_path(path: *const c_char, buf: *mut u8, bufsz: usize) -> isize {
-        super::xcanonical_path(CStr::from_ptr(path), slice::from_raw_parts_mut(buf, bufsz))
+        super::xcanonical_path(CStr::from_ptr(path), slice_from_ptr_mut(buf, bufsz))
     }
 
     #[no_mangle]
     unsafe extern "C" fn xreadlink(path: *const c_char, buf: *mut u8, bufsz: usize) -> isize {
-        super::xreadlink(CStr::from_ptr(path), slice::from_raw_parts_mut(buf, bufsz))
+        super::xreadlink(CStr::from_ptr(path), slice_from_ptr_mut(buf, bufsz))
     }
 
     #[no_mangle]