From 1d5179eb7180841dea36bd14a1c7b26d94220f95 Mon Sep 17 00:00:00 2001
From: Josh Megnauth <jo.sh@tutanota.com>
Date: Fri, 18 Apr 2025 01:39:16 -0400
Subject: [PATCH] Const calculate buffer size for strerror

The current buffer size is hard set to 256. Using const evaluation, the
maximum buf size can be calculated at compile time.
---
 src/header/errno/mod.rs  | 32 +++++++++++++++++++++++++++++++-
 src/header/string/mod.rs | 12 +++++-------
 tests/error.c            | 36 +++++++++++++++++++++++++++++++-----
 3 files changed, 67 insertions(+), 13 deletions(-)

diff --git a/src/header/errno/mod.rs b/src/header/errno/mod.rs
index b9c6f1510d..5ad3493e2d 100644
--- a/src/header/errno/mod.rs
+++ b/src/header/errno/mod.rs
@@ -178,7 +178,7 @@ pub const EOWNERDEAD: c_int = 130; /* Owner died */
 pub const ENOTRECOVERABLE: c_int = 131; /* State not recoverable */
 
 /// String representations for the respective `errno` values.
-pub static STR_ERROR: [&'static str; 132] = [
+pub const STR_ERROR: [&str; 132] = [
     "Success",
     "Operation not permitted",
     "No such file or directory",
@@ -312,3 +312,33 @@ pub static STR_ERROR: [&'static str; 132] = [
     "Owner died",
     "State not recoverable",
 ];
+
+/// Longest error message length
+pub const STRERROR_MAX: usize = {
+    // Number of digits of the max value of this platform's c_int
+    let digits = {
+        let mut len = 0;
+        let mut i = c_int::MAX;
+
+        while i > 0 {
+            i /= 10;
+            len += 1;
+        }
+
+        len
+    };
+
+    let mut longest: usize = "Unknown error: ".len() + digits + 1;
+
+    let mut i = 0;
+    while i < STR_ERROR.len() {
+        let len = STR_ERROR[i].len() + 1;
+        if len > longest {
+            longest = len;
+        }
+
+        i += 1;
+    }
+
+    longest
+};
diff --git a/src/header/string/mod.rs b/src/header/string/mod.rs
index 852108e708..1afb20c0a5 100644
--- a/src/header/string/mod.rs
+++ b/src/header/string/mod.rs
@@ -447,15 +447,13 @@ pub unsafe extern "C" fn strdup(s1: *const c_char) -> *mut c_char {
 pub unsafe extern "C" fn strerror(errnum: c_int) -> *mut c_char {
     use core::fmt::Write;
 
-    static mut strerror_buf: [u8; 256] = [0; 256];
-
+    static mut strerror_buf: [u8; STRERROR_MAX] = [0; STRERROR_MAX];
     let mut w = platform::StringWriter(strerror_buf.as_mut_ptr(), strerror_buf.len());
 
-    if errnum >= 0 && errnum < STR_ERROR.len() as c_int {
-        let _ = w.write_str(STR_ERROR[errnum as usize]);
-    } else {
-        let _ = w.write_fmt(format_args!("Unknown error {}", errnum));
-    }
+    let _ = match STR_ERROR.get(errnum as usize) {
+        Some(e) => w.write_str(e),
+        None => w.write_fmt(format_args!("Unknown error {}", errnum)),
+    };
 
     strerror_buf.as_mut_ptr() as *mut c_char
 }
diff --git a/tests/error.c b/tests/error.c
index 4170e1f4be..1dbf13703d 100644
--- a/tests/error.c
+++ b/tests/error.c
@@ -1,7 +1,10 @@
-#include <unistd.h>
-#include <stdio.h>
-#include <string.h>
+#include <err.h>
 #include <errno.h>
+#include <limits.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
 
 #include "test_helpers.h"
 
@@ -12,15 +15,38 @@ int main(void) {
     printf("errno: %d = %s\n", err, strerror(errno));
     perror("perror");
 
-    char buf1[256];
+    char buf1[256] = {0};
     int ret1 = strerror_r(err, buf1, 256);
     printf("errno: %d = %s, return: %d\n", err, buf1, ret1);
 
-    char buf2[3];
+    char buf2[3] = {0};
     int ret2 = strerror_r(err, buf2, 3);
     printf("errno: %d = %s, return: %d\n", err, buf2, ret2);
 
     char buf3[256] = {0};
     int ret3 = strerror_r(err, buf3, 0);
     printf("errno: %d = %s, return: %d\n", err, buf3, ret3);
+
+    // Test that the statically allocated buffer doesn't overflow
+    for (int code = EPERM; code < ENOTRECOVERABLE; ++code) {
+        const char* message = strerror(code);
+        if (!message) {
+            errx(EXIT_FAILURE,
+                 "Expected message for error code: %d",
+                 code
+            );
+        }
+    }
+
+    const char* actual_error = strerror(INT_MAX);
+    char expected_error[256] = {0};
+    sprintf(expected_error, "Unknown error %d", INT_MAX);
+    if (strncmp(expected_error, actual_error, 25) != 0) {
+        errx(EXIT_FAILURE,
+             "Expected: %s\nGot: %s",
+             expected_error, actual_error
+        );
+    }
+
+    return EXIT_SUCCESS;
 }