stack smashing detected

[eworm-de]

Compiling the latest yubico-pam code from git (2.13-23-g96cf010) works, but if
gcc had option '-fstack-protector' programs crash when authenticating CR:

*** stack smashing detected ***: su terminated
======= Backtrace: =========
/usr/lib/libc.so.6(+0x72ecf)[0x7fa27df6eecf]
/usr/lib/libc.so.6(__fortify_fail+0x37)[0x7fa27dff1c37]
/usr/lib/libc.so.6(__fortify_fail+0x0)[0x7fa27dff1c00]
/usr/lib/security/pam_yubico.so(pam_sm_authenticate+0x10fd)[0x7fa27cb2aecd]
/usr/lib/libpam.so.0(+0x2e8f)[0x7fa27e4ade8f]
/usr/lib/libpam.so.0(pam_authenticate+0x30)[0x7fa27e4ad6e0]
su[0x403563]
/usr/lib/libc.so.6(__libc_start_main+0xf5)[0x7fa27df1dbc5]
su[0x4023a1]

Increasing char buf[] to 125 in do_challenge_response() "fixes" the problem, though this is just undefined behaviour I think. I used memset() to clear buf with null bytes, looks like nothing is written to addresses beyond 0x19 (or similar, but far away from 0x7D).

This is an Arch Linux x86_64 system with these package versions:
linux 3.11.1-1
pam 1.1.6-4
gcc-multilib 4.8.1-3
glibc 2.18-4

[klali]

it seems this only happens with gcc 4.8

[eworm-de]

Remember I said it works with char buf[125]? Well, sizeof(state) is 124, so I bet it is related to that...
Still thinking about the real problem, though.