(build) crash in dcrypt when "-Bsymbolic-functions" is used on linking

[Aki Tuomi]

On 26.10.2016 15:29, Aki Tuomi wrote:
>
>
> On 26.10.2016 13:48, Christian Ehrhardt wrote:
>> Hi,
>> I was wondering about a crash when building dovecot 2.2.25 on latest
>> Ubuntu.
>> I wondered as I've had the same source building on Debian just fine.
>>
>> Some debugging led me to this weird behavior:
>> Using this gdb command file called autoreportissue in my case:
>> break dcrypt_initialize
>>   commands
>>     p dcrypt_vfs
>>     p &dcrypt_vfs
>>     watch dcrypt_vfs
>>     c
>>   end
>> break dcrypt_set_vfs
>>   commands
>>     p dcrypt_vfs
>>     p &dcrypt_vfs
>>     c
>>   end
>> r
>>
>> Running test-crypto on Debian and Ubuntu reported those two behaviours:
>> gdb -d /root/dovecot-2.2.25/src/ -x autoreportissue ./test-crypto
>>
>> Good:
>> Breakpoint 1, dcrypt_initialize (backend=0x555555587c02 "openssl",
>> set=0x0, error_r=0x0) at dcrypt.c:15
>> 15              if (dcrypt_vfs != NULL) {
>> $1 = (struct dcrypt_vfs *) 0x0
>> $2 = (struct dcrypt_vfs **) 0x555555796370 <dcrypt_vfs>
>> Hardware watchpoint 3: dcrypt_vfs
>> Breakpoint 2, dcrypt_set_vfs (vfs=0x7ffff7835020
>> <dcrypt_openssl_vfs>) at dcrypt.c:56
>> 56              dcrypt_vfs = vfs;
>> $3 = (struct dcrypt_vfs *) 0x0
>> $4 = (struct dcrypt_vfs **) 0x555555796370 <dcrypt_vfs>
>> Hardware watchpoint 3: dcrypt_vfs
>> Old value = (struct dcrypt_vfs *) 0x0
>> New value = (struct dcrypt_vfs *) 0x7ffff7835020 <dcrypt_openssl_vfs>
>> dcrypt_set_vfs (vfs=0x7ffff7835020 <dcrypt_openssl_vfs>) at dcrypt.c:57
>> 57      }
>>
>> Bad:
>> Breakpoint 1, dcrypt_initialize (backend=0x555555589f02 "openssl",
>> set=0x0, error_r=0x0) at dcrypt.c:11
>> 11      {
>> $1 = (struct dcrypt_vfs *) 0x0
>> $2 = (struct dcrypt_vfs **) 0x555555798370 <dcrypt_vfs>
>> Hardware watchpoint 3: dcrypt_vfs
>> Breakpoint 2, dcrypt_set_vfs (vfs=0x7ffff780a020
>> <dcrypt_openssl_vfs>) at dcrypt.c:56
>> 56              dcrypt_vfs = vfs;
>> $3 = (struct dcrypt_vfs *) 0x0
>> $4 = (struct dcrypt_vfs **) 0x7ffff780a890 <dcrypt_vfs>
>> Panic: file dcrypt.c: line 34 (dcrypt_initialize): assertion failed:
>> (dcrypt_vfs != NULL)
>> Error: Raw backtrace:
>> /root/dovecot-2.2.25/src/lib-dcrypt/test-crypto(+0x15f7c)
>> [0x555555569f7c] ->
>> /root/dovecot-2.2.25/src/lib-dcrypt/test-crypto(default_error_handler+0)
>> [0x55555556a030] ->
>> /root/dovecot-2.2.25/src/lib-dcrypt/test-crypto(i_fatal+0)
>> [0x55555556a2ff] ->
>> /root/dovecot-2.2.25/src/lib-dcrypt/test-crypto(dcrypt_initialize+0x140)
>> [0x55555555f030] ->
>> /root/dovecot-2.2.25/src/lib-dcrypt/test-crypto(main+0x23)
>> [0x55555556706d] ->
>> /lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xf1)
>> [0x7ffff782d3f1] ->
>> /root/dovecot-2.2.25/src/lib-dcrypt/test-crypto(_start+0x2a)
>> [0x55555555edea]
>> Program received signal SIGABRT, Aborted.
>>
>> One can see that in the bad case the pointer of dcrypt_vfs is
>> pointing to something of the scope of the .libs/libdcrypt_openssl.so
>> file and not the dcrypt_initialize of test-crypto.
>>
>> That made me wonder even more - where would this issue of variable
>> scope come from. After more debugging I found that the linker flag
>> "-Bsymbolic-functions" is the reason. This is default on recent
>> Ubuntu, but not on Debian (?yet?).
>>
>> Eventually what happens is that the dcrypt_vfs becomes part of the
>> .libs/libdcrypt_openssl.so. So the call from there to dcrypt_set_vfs
>> ends up setting not the expected variable.
>> I was unable to come up with a reasonable fix since I'm not enough
>> into your sublib structure.
>>
>> For now I assume I'm gonna build the package stripping this flag in
>> Ubuntu.
>> But long term I think dovecot should fix it to work with that
>> compiler flag.
>> Therefore the report to make you aware.
>>
>>
>> P.S. thanks to the dovecot community for having unit tests that find
>> this at build time!
>>
>> -- 
>> Christian Ehrhardt
>> Software Engineer, Ubuntu Server
>> Canonical Ltd
>
>
> Hi!
>
> Thank you for reporting this, we'll look into it.
>
> Aki Tuomi
> Dovecot oy

Hi!

We believe this is fixed in 2.2.26, with
https://github.com/dovecot/core/commit/452d0005a47c6872590346f5ea8b247974689ac9,
can you please retry with -Bsymbolic?

Aki