https://bugs.kde.org/show_bug.cgi?id=401284
Bug ID: 401284
Summary: False positive "Source and destination overlap in
strncat"
Product: valgrind
Version: unspecified
Platform: Other
OS: Linux
Status: REPORTED
Severity: normal
Priority: NOR
Component: memcheck
Assignee: jsew...@acm.org
Reporter: l...@ncbi.nlm.nih.gov
Target Milestone: ---
SUMMARY
Valgrind reports:
Source and destination overlap in strncat(0x4c33045, 0x4c33040, 5)
which is, given the argument values, an impossible situation: strncat() will
not take more than 5 bytes from the location pointed to by second argument,
0x4c33040, that is, the range 0x4c33040-0x4c33044 (if not fewer, should a '\0'
be encountered within), but the destination address is out of that range (yet
indeed right adjacent to the source area). But there's no error here.
STEPS TO REPRODUCE
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main(int argc, char* argv[])
{
size_t len = strlen(argv[1]);
char* buf = (char*) malloc(2 * len + 1);
memcpy(buf, argv[1], len + 1);
strncat(buf + len, buf, len);
printf("%s\n", buf);
free(buf);
return 0;
}
OBSERVED RESULT
$ gcc -Wall -o vbug vbug.c
$ ./vbug hello
hellohello
$ valgrind ./vbug hello
==10915== Memcheck, a memory error detector
==10915== Copyright (C) 2002-2015, and GNU GPL'd, by Julian Seward et al.
==10915== Using Valgrind-3.11.0 and LibVEX; rerun with -h for copyright info
==10915== Command: ./vbug hello
==10915==
==10915== Source and destination overlap in strncat(0x4c33045, 0x4c33040, 5)
==10915== at 0x4A08A76: strncat (vg_replace_strmem.c:344)
==10915== by 0x4006D0: main (in /home/lavr/vbug)
==10915==
hellohello
==10915==
==10915== HEAP SUMMARY:
==10915== in use at exit: 0 bytes in 0 blocks
==10915== total heap usage: 1 allocs, 1 frees, 11 bytes allocated
==10915==
==10915== All heap blocks were freed -- no leaks are possible
==10915==
==10915== For counts of detected and suppressed errors, rerun with: -v
==10915== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 6 from 5)
EXPECTED RESULT
No errors
SOFTWARE/OS VERSIONS
Linux:
uname -a
Linux hostname 2.6.32-754.6.3.el6.x86_64 #1 SMP Tue Oct 9 17:27:49 UTC 2018
x86_64 x86_64 x86_64 GNU/Linux
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