50a717a67b
Add notes to each of these that specifically state that results are undefined if the strings overlap. In the case of memcpy, we document the overlapping behavior on FreeBSD (pre-existing). For str*, it is left unspecified, however, since the default (and x86) implementations do not handle overlapping strings properly. PR: 223653 Sponsored by: Netflix
166 lines
4.3 KiB
Groff
166 lines
4.3 KiB
Groff
.\" Copyright (c) 1990, 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" This code is derived from software contributed to Berkeley by
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.\" Chris Torek and the American National Standards Committee X3,
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.\" on Information Processing Systems.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)strcat.3 8.1 (Berkeley) 6/4/93
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.\" $FreeBSD$
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.\"
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.Dd December 1, 2009
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.Dt STRCAT 3
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.Os
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.Sh NAME
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.Nm strcat ,
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.Nm strncat
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.Nd concatenate strings
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In string.h
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.Ft char *
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.Fn strcat "char * restrict s" "const char * restrict append"
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.Ft char *
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.Fn strncat "char * restrict s" "const char * restrict append" "size_t count"
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.Sh DESCRIPTION
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The
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.Fn strcat
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and
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.Fn strncat
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functions
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append a copy of the null-terminated string
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.Fa append
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to the end of the null-terminated string
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.Fa s ,
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then add a terminating
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.Ql \e0 .
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The string
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.Fa s
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must have sufficient space to hold the result.
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If
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.Fa s
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and
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.Fa append
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overlap, the results are undefined.
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.Pp
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The
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.Fn strncat
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function
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appends not more than
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.Fa count
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characters from
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.Fa append ,
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and then adds a terminating
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.Ql \e0 .
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If
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.Fa s
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and
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.Fa append
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overlap, the results are undefined.
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.Sh RETURN VALUES
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The
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.Fn strcat
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and
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.Fn strncat
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functions
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return the pointer
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.Fa s .
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.Sh SEE ALSO
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.Xr bcopy 3 ,
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.Xr memccpy 3 ,
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.Xr memcpy 3 ,
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.Xr memmove 3 ,
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.Xr strcpy 3 ,
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.Xr strlcat 3 ,
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.Xr strlcpy 3 ,
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.Xr wcscat 3
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.Sh STANDARDS
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The
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.Fn strcat
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and
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.Fn strncat
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functions
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conform to
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.St -isoC .
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.Sh SECURITY CONSIDERATIONS
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The
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.Fn strcat
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function is easily misused in a manner
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which enables malicious users to arbitrarily change
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a running program's functionality through a buffer overflow attack.
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.Pp
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Avoid using
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.Fn strcat .
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Instead, use
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.Fn strncat
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or
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.Fn strlcat
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and ensure that no more characters are copied to the destination buffer
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than it can hold.
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.Pp
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Note that
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.Fn strncat
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can also be problematic.
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It may be a security concern for a string to be truncated at all.
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Since the truncated string will not be as long as the original,
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it may refer to a completely different resource
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and usage of the truncated resource
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could result in very incorrect behavior.
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Example:
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.Bd -literal
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void
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foo(const char *arbitrary_string)
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{
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char onstack[8];
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#if defined(BAD)
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/*
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* This first strcat is bad behavior. Do not use strcat!
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*/
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(void)strcat(onstack, arbitrary_string); /* BAD! */
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#elif defined(BETTER)
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/*
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* The following two lines demonstrate better use of
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* strncat().
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*/
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(void)strncat(onstack, arbitrary_string,
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sizeof(onstack) - strlen(onstack) - 1);
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#elif defined(BEST)
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/*
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* These lines are even more robust due to testing for
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* truncation.
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*/
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if (strlen(arbitrary_string) + 1 >
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sizeof(onstack) - strlen(onstack))
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err(1, "onstack would be truncated");
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(void)strncat(onstack, arbitrary_string,
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sizeof(onstack) - strlen(onstack) - 1);
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#endif
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}
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.Ed
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