Re: [libmicrohttpd] Three runtime errors in tests with UBSAN

[Christian Grothoff]

On 02/27/2018 10:39 AM, Tim Rühsen wrote:
> $ CC=gcc CFLAGS="-O0 -g -ggdb3 -fno-omit-frame-pointer
> -fsanitize=undefined" ./configure
> 
> $ make clean
> $ make check
> $ grep runtime src/*/*.log
> 
> src/microhttpd/test_upgrade.log:test_upgrade.c:1075:32: runtime error:
> member access within misaligned address 0x560144586014 for type 'const
> union MHD_DaemonInfo', which requires 8 byte alignment
> 
> src/microhttpd/test_upgrade_tls.log:test_upgrade.c:1075:32: runtime
> error: member access within misaligned address 0x55cea9a95014 for type
> 'const union MHD_DaemonInfo', which requires 8 byte alignment

I'm not sure I agree with these two, as while we return a 'union' with
an 8-byte alignment, the only valid *field* we return is 16-bit, and the
union overall is read-only.  So reading the 16-bit field should be
perfectly safe from an alignment perspective (it is 16-bit aligned), and
everything else is a really bad idea (TM) anyway, as it would read garbage.

We could theoretically fix this, but to avoid ABI breakage this would
require using more memory (effectively reserving a fresh union for each
possible return case) and I do not see how this would gain anything for
anyone except making the sanitizer happy.

A better solution is of course the upcoming microhttpd2-API, which
avoids this issue entirely (by not returning a union).

For now, I've just hacked the testcase to memcpy() the port, which
doesn't actually improve the code but eliminates the warning. 8-)

> src/testcurl/test_put_chunked.log:test_put_chunked.c:107:16: runtime
> error: null pointer passed as argument 1, which is declared to never be null

Fixed.

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