158 lines
4.2 KiB
Groff
158 lines
4.2 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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.\" 4. 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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.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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.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 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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(See
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the FSA.)
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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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.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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