158f0484fSRodney W. Grimes.\" Copyright (c) 1990, 1991, 1993 258f0484fSRodney W. Grimes.\" The Regents of the University of California. All rights reserved. 358f0484fSRodney W. Grimes.\" 458f0484fSRodney W. Grimes.\" This code is derived from software contributed to Berkeley by 558f0484fSRodney W. Grimes.\" Chris Torek and the American National Standards Committee X3, 658f0484fSRodney W. Grimes.\" on Information Processing Systems. 758f0484fSRodney W. Grimes.\" 858f0484fSRodney W. Grimes.\" Redistribution and use in source and binary forms, with or without 958f0484fSRodney W. Grimes.\" modification, are permitted provided that the following conditions 1058f0484fSRodney W. Grimes.\" are met: 1158f0484fSRodney W. Grimes.\" 1. Redistributions of source code must retain the above copyright 1258f0484fSRodney W. Grimes.\" notice, this list of conditions and the following disclaimer. 1358f0484fSRodney W. Grimes.\" 2. Redistributions in binary form must reproduce the above copyright 1458f0484fSRodney W. Grimes.\" notice, this list of conditions and the following disclaimer in the 1558f0484fSRodney W. Grimes.\" documentation and/or other materials provided with the distribution. 1658f0484fSRodney W. Grimes.\" 3. All advertising materials mentioning features or use of this software 1758f0484fSRodney W. Grimes.\" must display the following acknowledgement: 1858f0484fSRodney W. Grimes.\" This product includes software developed by the University of 1958f0484fSRodney W. Grimes.\" California, Berkeley and its contributors. 2058f0484fSRodney W. Grimes.\" 4. Neither the name of the University nor the names of its contributors 2158f0484fSRodney W. Grimes.\" may be used to endorse or promote products derived from this software 2258f0484fSRodney W. Grimes.\" without specific prior written permission. 2358f0484fSRodney W. Grimes.\" 2458f0484fSRodney W. Grimes.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 2558f0484fSRodney W. Grimes.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 2658f0484fSRodney W. Grimes.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 2758f0484fSRodney W. Grimes.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 2858f0484fSRodney W. Grimes.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 2958f0484fSRodney W. Grimes.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 3058f0484fSRodney W. Grimes.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 3158f0484fSRodney W. Grimes.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 3258f0484fSRodney W. Grimes.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 3358f0484fSRodney W. Grimes.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 3458f0484fSRodney W. Grimes.\" SUCH DAMAGE. 3558f0484fSRodney W. Grimes.\" 3658f0484fSRodney W. Grimes.\" @(#)strcat.3 8.1 (Berkeley) 6/4/93 377f3dea24SPeter Wemm.\" $FreeBSD$ 3858f0484fSRodney W. Grimes.\" 3958f0484fSRodney W. Grimes.Dd June 4, 1993 4058f0484fSRodney W. Grimes.Dt STRCAT 3 4158f0484fSRodney W. Grimes.Os 4258f0484fSRodney W. Grimes.Sh NAME 4358f0484fSRodney W. Grimes.Nm strcat 4458f0484fSRodney W. Grimes.Nd concatenate strings 4525bb73e0SAlexey Zelkin.Sh LIBRARY 4625bb73e0SAlexey Zelkin.Lb libc 4758f0484fSRodney W. Grimes.Sh SYNOPSIS 4832eef9aeSRuslan Ermilov.In string.h 4958f0484fSRodney W. Grimes.Ft char * 5058f0484fSRodney W. Grimes.Fn strcat "char *s" "const char *append" 5158f0484fSRodney W. Grimes.Ft char * 5258f0484fSRodney W. Grimes.Fn strncat "char *s" "const char *append" "size_t count" 5358f0484fSRodney W. Grimes.Sh DESCRIPTION 5458f0484fSRodney W. GrimesThe 5558f0484fSRodney W. Grimes.Fn strcat 5658f0484fSRodney W. Grimesand 5758f0484fSRodney W. Grimes.Fn strncat 5858f0484fSRodney W. Grimesfunctions 5958f0484fSRodney W. Grimesappend a copy of the null-terminated string 6058f0484fSRodney W. Grimes.Fa append 6158f0484fSRodney W. Grimesto the end of the null-terminated string 6258f0484fSRodney W. Grimes.Fa s , 6358f0484fSRodney W. Grimesthen add a terminating 6458f0484fSRodney W. Grimes.Ql \e0 . 6558f0484fSRodney W. GrimesThe string 6658f0484fSRodney W. Grimes.Fa s 6758f0484fSRodney W. Grimesmust have sufficient space to hold the result. 6858f0484fSRodney W. Grimes.Pp 6958f0484fSRodney W. GrimesThe 7058f0484fSRodney W. Grimes.Fn strncat 7158f0484fSRodney W. Grimesfunction 7258f0484fSRodney W. Grimesappends not more than 7358f0484fSRodney W. Grimes.Fa count 7459f00bcdSMike Pritchardcharacters from 7559f00bcdSMike Pritchard.Fa append , 7659f00bcdSMike Pritchardand then adds a terminating 7759f00bcdSMike Pritchard.Ql \e0 . 7858f0484fSRodney W. Grimes.Sh RETURN VALUES 7958f0484fSRodney W. GrimesThe 8058f0484fSRodney W. Grimes.Fn strcat 8158f0484fSRodney W. Grimesand 8258f0484fSRodney W. Grimes.Fn strncat 8358f0484fSRodney W. Grimesfunctions 8458f0484fSRodney W. Grimesreturn the pointer 8558f0484fSRodney W. Grimes.Fa s . 8641f91cb4SChris Costello.Sh SECURITY CONSIDERATIONS 8741f91cb4SChris CostelloThe 8841f91cb4SChris Costello.Fn strcat 8941f91cb4SChris Costellofunction is easily misused in a manner 9041f91cb4SChris Costellowhich enables malicious users to arbitrarily change 9141f91cb4SChris Costelloa running program's functionality through a buffer overflow attack. 9241f91cb4SChris Costello(See 9341f91cb4SChris Costellothe FSA.) 9441f91cb4SChris Costello.Pp 9541f91cb4SChris CostelloAvoid using 9641f91cb4SChris Costello.Fn strcat . 9741f91cb4SChris CostelloInstead, use 9841f91cb4SChris Costello.Fn strncat 9941f91cb4SChris Costelloor 10041f91cb4SChris Costello.Fn strlcat 10141f91cb4SChris Costelloand ensure that no more characters are copied to the destination buffer 10241f91cb4SChris Costellothan it can hold. 10341f91cb4SChris Costello.Pp 10441f91cb4SChris CostelloNote that 10541f91cb4SChris Costello.Fn strncat 10641f91cb4SChris Costellocan also be problematic. 10741f91cb4SChris CostelloIt may be a security concern for a string to be truncated at all. 10841f91cb4SChris CostelloSince the truncated string will not be as long as the original, 10941f91cb4SChris Costelloit may refer to a completely different resource 11041f91cb4SChris Costelloand usage of the truncated resource 11141f91cb4SChris Costellocould result in very incorrect behavior. 11241f91cb4SChris CostelloExample: 11341f91cb4SChris Costello.Bd -literal 11441f91cb4SChris Costellovoid 11541f91cb4SChris Costellofoo(const char *arbitrary_string) 11641f91cb4SChris Costello{ 11741f91cb4SChris Costello char onstack[8]; 11841f91cb4SChris Costello 11941f91cb4SChris Costello#if defined(BAD) 12041f91cb4SChris Costello /* 12141f91cb4SChris Costello * This first strcat is bad behavior. Do not use strcat! 12241f91cb4SChris Costello */ 12341f91cb4SChris Costello (void)strcat(onstack, arbitrary_string); /* BAD! */ 12441f91cb4SChris Costello#elif defined(BETTER) 12541f91cb4SChris Costello /* 12641f91cb4SChris Costello * The following two lines demonstrate better use of 12741f91cb4SChris Costello * strncat(). 12841f91cb4SChris Costello */ 12941f91cb4SChris Costello (void)strncat(onstack, arbitrary_string, 13041f91cb4SChris Costello sizeof(onstack) - strlen(onstack) - 1); 13141f91cb4SChris Costello#elif defined(BEST) 13241f91cb4SChris Costello /* 13341f91cb4SChris Costello * These lines are even more robust due to testing for 13441f91cb4SChris Costello * truncation. 13541f91cb4SChris Costello */ 13641f91cb4SChris Costello if (strlen(arbitrary_string) + 1 > 13741f91cb4SChris Costello sizeof(onstack) - strlen(onstack)) 13841f91cb4SChris Costello err(1, "onstack would be truncated"); 13941f91cb4SChris Costello (void)strncat(onstack, arbitrary_string, 14041f91cb4SChris Costello sizeof(onstack) - strlen(onstack) - 1); 14141f91cb4SChris Costello#endif 14241f91cb4SChris Costello} 14341f91cb4SChris Costello 14441f91cb4SChris Costello.Ed 14558f0484fSRodney W. Grimes.Sh SEE ALSO 14658f0484fSRodney W. Grimes.Xr bcopy 3 , 14758f0484fSRodney W. Grimes.Xr memccpy 3 , 14858f0484fSRodney W. Grimes.Xr memcpy 3 , 14958f0484fSRodney W. Grimes.Xr memmove 3 , 1504e2abf95SWarner Losh.Xr strcpy 3 , 1514e2abf95SWarner Losh.Xr strlcat 3 , 1524e2abf95SWarner Losh.Xr strlcpy 3 15341f91cb4SChris Costello.Rs 15441f91cb4SChris Costello.%T "The FreeBSD Security Architecture" 15541f91cb4SChris Costello.%J "/usr/share/doc/{to be decided}" 15641f91cb4SChris Costello.Re 15758f0484fSRodney W. Grimes.Sh STANDARDS 15858f0484fSRodney W. GrimesThe 15958f0484fSRodney W. Grimes.Fn strcat 16058f0484fSRodney W. Grimesand 16158f0484fSRodney W. Grimes.Fn strncat 16258f0484fSRodney W. Grimesfunctions 16358f0484fSRodney W. Grimesconform to 164588a200cSRuslan Ermilov.St -isoC . 165