MSAN: `strlcpy` and `strlcat` is not supported

[pkillarjun]

Glibc commit Implement strlcpy and strlcat.

Built environment

$ clang -v
clang version 18.1.8 (Fedora 18.1.8-1.fc40)
Target: x86_64-redhat-linux-gnu
Thread model: posix
InstalledDir: /usr/bin
Configuration file: /etc/clang/x86_64-redhat-linux-gnu-clang.cfg
System configuration file directory: /etc/clang/
Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-redhat-linux/14
Selected GCC installation: /usr/bin/../lib/gcc/x86_64-redhat-linux/14
Candidate multilib: .;@m64
Candidate multilib: 32;@m32
Selected multilib: .;@m64

$ ldd --version
ldd (GNU libc) 2.39
Copyright (C) 2024 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
Written by Roland McGrath and Ulrich Drepper.

$ uname -a
Linux fedora 6.11.4-201.fc40.x86_64 #1 SMP PREEMPT_DYNAMIC Sun Oct 20 15:04:22 UTC 2024 x86_64 GNU/Linux

test code

/* msan_strlcpy_test.c */

#include <stdio.h>
#include <string.h>

// https://sourceware.org/git/?p=glibc.git;a=blob;f=string/strlcpy.c;h=c6c33b1e33d601c66776ea6eec1b0c8f8ed696a9;hb=ef321e23c20eebc6d6fb4044425c00e6df27b05f
size_t
__strlcpy (char *__restrict dest, const char *__restrict src, size_t size)
{
  size_t src_length = strlen (src);

  if (__glibc_unlikely (src_length >= size))
    {
      if (size > 0)
        {
          /* Copy the leading portion of the string.  The last
             character is subsequently overwritten with the NUL
             terminator, but the destination size is usually a
             multiple of a small power of two, so writing it twice
             should be more efficient than copying an odd number of
             bytes.  */
          memcpy (dest, src, size);
          dest[size - 1] = '\0';
        }
    }
  else
    /* Copy the string and its terminating NUL character.  */
    memcpy (dest, src, src_length + 1);
  return src_length;
}

int main()
{
    char defname[256];

    // The program won't crash here
    memset(defname, 0x00, 4);
    for (int i = 0; i < 4; i++) {
        printf("%02x ", defname[i]);
    }
    printf("\n");

    // The program won't crash here
    strncpy(defname, "AAAAAAAA", 8);
    for (int i = 0; i < 8; i++) {
        printf("%02x ", defname[i]);
    }
    printf("\n");

    // The program won't crash here
    __strlcpy(defname, "AAAAAAAAAAAA", 12);
    for (int i = 0; i < 12; i++) {
        printf("%02x ", defname[i]);
    }
    printf("\n");

    // The program shouldn't crash, But it dose;
    strlcpy(defname, "AAAAAAAAAAAAAAAA", 16);
    for (int i = 0; i < 16; i++) {
        printf("%02x ", defname[i]);
    }
    printf("\n");
}

compile and run

$ clang -fsanitize=memory msan_strlcpy_test.c -o msan_strlcpy_test

$ ./msan_strlcpy_test
00 00 00 00 
41 41 41 41 41 41 41 41 
41 41 41 41 41 41 41 41 41 41 41 00 
==154959==WARNING: MemorySanitizer: use-of-uninitialized-value
    #0 0x4c8d6d in main (/home/down/Desktop/msan_strlcpy_test+0x4c8d6d) (BuildId: 90183bc646d4995b7cd61af36dece204d375dd3e)
    #1 0x7f03337af087 in __libc_start_call_main (/lib64/libc.so.6+0x2a087) (BuildId: 77c77fee058b19c6f001cf2cb0371ce3b8341211)
    #2 0x7f03337af14a in __libc_start_main@GLIBC_2.2.5 (/lib64/libc.so.6+0x2a14a) (BuildId: 77c77fee058b19c6f001cf2cb0371ce3b8341211)
    #3 0x430304 in _start (/home/down/Desktop/msan_strlcpy_test+0x430304) (BuildId: 90183bc646d4995b7cd61af36dece204d375dd3e)

SUMMARY: MemorySanitizer: use-of-uninitialized-value (/home/down/Desktop/msan_strlcpy_test+0x4c8d6d) (BuildId: 90183bc646d4995b7cd61af36dece204d375dd3e) in main
Exiting

Ping @vitalybuka

[Explorer09]

For reference, strlcat() and strlcpy() are both part of POSIX.1-2024 now.