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

[Aki Tuomi]

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