On 12/5/22 16:49, Alejandro Colomar wrote:
Never use this function. Really. Cc: <pkg-shadow-devel@xxxxxxxxxxxxxxxxxxxxxxx> Cc: <libc-alpha@xxxxxxxxxxxxxx> Signed-off-by: Alejandro Colomar <alx@xxxxxxxxxx> --- Hi! To shadow-utils readers, I've seen there are a few uses of strncat(3) in shadow-utils. I'll review my current PR about string handling to also address this issue. To glibc readers, please bury this function deep down as if it were radioactive waste. Cheers, Alex
The rendered version of the new manual page for strncpy(3) is:
strncat(3) Library Functions Manual strncat(3)
NAME
strncat - concatenate two strings
LIBRARY
Standard C library (libc, -lc)
SYNOPSIS
#include <string.h>
[[deprecated]]
char *strncat(char dest[restrict strlen(.dest) + strnlen(.n) + 1],
const char src[restrict .n],
size_t n);
DESCRIPTION
Note: Never use this function.
For safe string concatenation, see strlcat(3bsd). For copying
or concatenating a string into a fixed‐length buffer with zero‐
ing of the rest, see stpncpy(3).
strncat() appends at most n characters of src to the end of dst.
It always terminates with a null character the string placed in
dest.
A simple implementation of strncat() might be:
char *
strncat(char *dest, const char *src, size_t n)
{
return memcpy(dest + strlen(dest), src, strnlen(src, n));
}
RETURN VALUE
strncat() returns a pointer to the resulting string dest.
ATTRIBUTES
For an explanation of the terms used in this section, see at‐
tributes(7).
┌─────────────────────────────────────┬───────────────┬─────────┐
│Interface │ Attribute │ Value │
├─────────────────────────────────────┼───────────────┼─────────┤
│strncat() │ Thread safety │ MT‐Safe │
└─────────────────────────────────────┴───────────────┴─────────┘
STANDARDS
POSIX.1‐2001, POSIX.1‐2008, C89, C99, SVr4, 4.3BSD.
BUGS
All. Seriously, there’s no use case for this function.
It has a very misleading name. This function has no relation‐
ship with strncpy(3).
Since it doesn’t know the size of the destination buffer, this
function can easily write past the end of the array, being an
open door to all kinds of crackers.
SEE ALSO
strcpy(3), string(3)
Linux man‐pages (unreleased) (date) strncat(3)
--
<http://www.alejandro-colomar.es/>
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