Re: exim fixing %n (from deraadt@)

On 9/20/21 11:32 AM, Stuart Henderson wrote:
> On 2021/09/20 10:29, Stuart Henderson wrote:
>> Some of these are pretty hairy and it's a moving codebase. Since they
>> are applying compiler "printf-like" attribute to functions which are
>> using their own functions rather than libc printf, and we are purely
>> making this change to disable the spurious warning because there is
>> no abort in their %n handling, can't we just disable the annotations
>> instead?
>
> actually my patch comment is too short, maybe this instead
>
> Don't do printf-like checks on Exim's internal printf-like functions on
> OpenBSD. libc printf functions abort() on %n use, and the compiler has
> been modified to warn about this; however this does not apply to Exim's
> functions which do still support %n.
>
>

This is more a political decision on what we are trying to solve here,
compiler warnings or secure coding practices. In the end, I would like
to have Theo's point of view.

>
>> Index: patches/patch-src_mytypes_h
>> ===================================================================
>> RCS file: patches/patch-src_mytypes_h
>> diff -N patches/patch-src_mytypes_h
>> --- /dev/null 1 Jan 1970 00:00:00 -0000
>> +++ patches/patch-src_mytypes_h 20 Sep 2021 09:28:21 -0000
>> @@ -0,0 +1,20 @@
>> +$OpenBSD$
>> +
>> +Don't do printf-like checks on OpenBSD, which warn about %n use.
>> +
>> +Index: src/mytypes.h
>> +--- src/mytypes.h.orig
>> ++++ src/mytypes.h
>> +@@ -33,7 +33,11 @@ local_scan.h includes it and exim.h includes them both
>> + the arguments of printf-like functions. This is done by a macro. */
>> +
>> + #if defined(__GNUC__) || defined(__clang__)
>> +-# define PRINTF_FUNCTION(A,B) __attribute__((format(printf,A,B)))
>> ++# if defined(__OpenBSD__)
>> ++# define PRINTF_FUNCTION(A,B) /**/
>> ++# else
>> ++# define PRINTF_FUNCTION(A,B) __attribute__((format(printf,A,B)))
>> ++# endif
>> + # define ARG_UNUSED __attribute__((__unused__))
>> + # define WARN_UNUSED_RESULT __attribute__((__warn_unused_result__))
>> + # define ALLOC __attribute__((malloc))
>>
>>
>>
>