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Re: [Bacula-devel] "buffer overflow detected" error on fedora distributions.


Please Note the following quote from the documentation on the implementation 
of FORTIFY_SOURCE=2

    With -D_FORTIFY_SOURCE=2 some more checking is added, but
    some conforming programs might fail.

Bacula is a conforming program (i.e. there is no buffer overrun at that 
point).

Best regards,

Kern

On Tuesday 29 January 2008 00.02:45 Michael Lausch wrote:
> The error is due to the new (well ~ core 5) buffer overflow checking
> implemented by gcc and glibc. _FORTIFY_SOURCE=2  activates it. what
> happens can be read in detail at
> http://gcc.gnu.org/ml/gcc-patches/2004-09/msg02055.html. but basically
> the error is a buffer overflow check in parse.c in the bacula library.
>
> In this file the following definition can be found:
> extern  CURES res_all;
> CURES is a type defined in the library with a size of, let's say 120
> bytes. the actual value is not important.
>
> In the bat module for example, the res_all variable is redefined as
> URES res_all;
> in bat_conf.cpp. URES is a type with, let's say, 250 bytes. The actual
> value is not important as long as it's larger then the size of the URES
> type defined in the library. The variable res_all_size is initialized to
> the size of the res_all variable, in my example to 250.
>
> In the init_resource() function in parse_conf.c is a call to
> memset(&res_all, 0, res_all_size);
> This call is replaced to a boundary checking memset() call as outlined
> by the example 2 in
> http://gcc.gnu.org/ml/gcc-patches/2004-09/msg02055.html
> The 3rd parameter of the memset call, res_all_size, which is 250, is
> checked against the size of the CURES type (120) and the buffer overflow
> error is raised by the boundary check of the memset function.
>
>
> The solution is to allocate the res_all variable dynamically.
>
> My quick hack solution was to change the definition of CURES to
> union CURES {
>    MSGS  res_msgs;
>    RES hdr;
>    char _space_[1024];
> };
> This makes the size of the CURES union larger than all the other unions
> defined in the different bacula executables and the memset check
> succeeds. But as i said this is a hack and i used it only as a band aid
> to get a runnable system.
>
> The solution to disable boundary checking by using a D_FORTIFY_SOURCE=0
> definition in the compiler command line should not be done, because
> checking for errors in such a sensible application as a backup utility
> is always a good thing.



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