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From: "matt at use dot net" <sourceware-bugzilla@sourceware.org>
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Subject: [Bug build/15017] New: potential buffer overflow uncovered by
 compiling with -O3 and FORTIFY_SOURCE
Date: Mon, 14 Jan 2013 22:41:00 -0000
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http://sourceware.org/bugzilla/show_bug.cgi?id=15017

             Bug #: 15017
           Summary: potential buffer overflow uncovered by compiling with
                    -O3 and FORTIFY_SOURCE
           Product: gdb
           Version: 7.5
            Status: NEW
          Severity: critical
          Priority: P2
         Component: build
        AssignedTo: unassigned@sourceware.org
        ReportedBy: matt@use.net
    Classification: Unclassified


I got this when compiling the latest Fedora source RPM (7.5.1-32). My default
CFLAGS is -O3 instead of the default -O2:

In function 'strncat',
    inlined from 'svr4_create_solib_event_breakpoints' at
../../gdb/solib-svr4.c:2076:
/usr/include/bits/string3.h:152: error: call to __builtin___strncat_chk might
overflow destination buffer


this correctly fails the build. The fix was simple, as the correct use of
strncat for the same data is one line below:
              if (with_prefix)
                strncat (name, "rtld_", sizeof (name));

              strncat (name, probe_info[i].name, sizeof (name) - sizeof
("rtld_"));

becomes

              if (with_prefix)
                strncat (name, "rtld_", sizeof (name) - sizeof("rtld_"));

              strncat (name, probe_info[i].name, sizeof (name) - sizeof
("rtld_"));


and this eliminates the warning/error.

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