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32 .\" @(#)strcat.3 8.1 (Berkeley) 6/4/93
41 .Nd concatenate strings
47 .Fn strcat "char * restrict s" "const char * restrict append"
49 .Fn strncat "char * restrict s" "const char * restrict append" "size_t count"
56 append a copy of the null-terminated string
58 to the end of the null-terminated string
60 then add a terminating
64 must have sufficient space to hold the result.
73 and then adds a terminating
100 .Sh SECURITY CONSIDERATIONS
103 function is easily misused in a manner
104 which enables malicious users to arbitrarily change
105 a running program's functionality through a buffer overflow attack.
115 and ensure that no more characters are copied to the destination buffer
120 can also be problematic.
121 It may be a security concern for a string to be truncated at all.
122 Since the truncated string will not be as long as the original,
123 it may refer to a completely different resource
124 and usage of the truncated resource
125 could result in very incorrect behavior.
129 foo(const char *arbitrary_string)
135 * This first strcat is bad behavior. Do not use strcat!
137 (void)strcat(onstack, arbitrary_string); /* BAD! */
138 #elif defined(BETTER)
140 * The following two lines demonstrate better use of
143 (void)strncat(onstack, arbitrary_string,
144 sizeof(onstack) - strlen(onstack) - 1);
147 * These lines are even more robust due to testing for
150 if (strlen(arbitrary_string) + 1 >
151 sizeof(onstack) - strlen(onstack))
152 err(1, "onstack would be truncated");
153 (void)strncat(onstack, arbitrary_string,
154 sizeof(onstack) - strlen(onstack) - 1);