[GUACAMOLE-720] Build failure with GCC 9

• Type: Bug
• Status: Closed
• Priority: Minor
• Resolution: Duplicate
• Affects Version/s: 1.0.0
• Component/s: guacd
• Flags: Important
• Assignee: Unassigned
• Reporter: Simone Caronni
• Created: 26/Jan/19 13:29
• Updated: 29/Apr/19 01:59
• Resolved: 29/Apr/19 01:59

Description

In particular GCC 9 complains about this code:

> BUILDSTDERR: In file included from /usr/include/string.h:494,
> BUILDSTDERR:                  from /usr/include/winpr/collections.h:25,
> BUILDSTDERR:                  from /usr/include/freerdp/types.h:80,
> BUILDSTDERR:                  from /usr/include/freerdp/svc.h:24,
> BUILDSTDERR:                  from /usr/include/freerdp/utils/svc_plugin.h:27,
> BUILDSTDERR:                  from ./rdp_svc.h:25,
> BUILDSTDERR:                  from guac_svc/svc_service.h:24,
> BUILDSTDERR:                  from guac_svc/svc_service.c:22:
> BUILDSTDERR: In function 'strncpy',
> BUILDSTDERR:     inlined from 'VirtualChannelEntry' at guac_svc/svc_service.c:56:5:
> BUILDSTDERR: /usr/include/bits/string_fortified.h:106:10: error: '__builtin_strncpy' output may be truncated copying 7 bytes from a string of length 7 [-Werror=stringop-truncation]
> BUILDSTDERR:   106 |   return __builtin___strncpy_chk (__dest, __src, __len, __bos (__dest));
> BUILDSTDERR:       |          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> BUILDSTDERR: cc1: all warnings being treated as errors

Which stems from this code:

>   /* Init channel def */
>     strncpy(svc_plugin->[plugin.channel_def.name|http://plugin.channel_def.name/], svc->name,
>             GUAC_RDP_SVC_MAX_LENGTH);

The compiler is complaining because it can not prove the resulting string has a proper NUL terminator.  This can cause runtime faults and even  security issues.

Most folks are fixing this by either NUL terminating the string after the call to strncpy .  However, in some cases the string is not guaranteed to be NUL terminated – in those cases the "nonstring" attribute is more appropriate.  Note that using "nonstring" will cause the compiler to analyze use points and warn if you pass a "nonstring" variable to a routine that expects a properly terminated NUL string such as strlen.

Issue Links

• duplicates: GUACAMOLE-637 Compile error: 'strncpy' output may be truncated copying 7 bytes from a string of length 7