Date: Sat, 18 May 2019 16:14:28 +0200 From: Andrea Venturoli <ml@netfence.it> To: Jan Beich <jbeich@FreeBSD.org> Cc: Konstantin Belousov <kostikbel@gmail.com>, timur@FreeBSD.org, freebsd-ports@freebsd.org Subject: Re: Samba dump (useless) core Message-ID: <f89679c2-0610-c533-3f3a-2496993ce187@netfence.it> In-Reply-To: <k1f1-uq4m-wny@FreeBSD.org> References: <169305b9-64ea-6305-8ef2-9c11b8c9baf3@netfence.it> <20190508102504.GY2748@kib.kiev.ua> <0eb47166-ddaf-d0ed-7730-91341634c72c@netfence.it> <k1f1-uq4m-wny@FreeBSD.org>
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On 5/8/19 1:44 PM, Jan Beich wrote: Hello. While I am by no means at the end of this, I'll post some updates. > "stack overflow detected" messages are part of -fstack-protector*. > Recently, ports/ default changed to -strong in order to follow base/. > > https://svnweb.freebsd.org/changeset/ports/499897 Reading the description of -fstack-protector vs -fstack-protector-strong, it shouldn't make any difference in this function. I tried "SSP_CFLAGS?= -fstack-protector" for confirmation and the canary is still there. So that changeset cannot be the culprit. I do no dare trying "SSP_UNSAFE= yes", because, in case it's really a buffer overflow, I prefer a core to undefined behaviour on production servers! Perhaps it's lack of imagination on my part, but I fail to see how SSP could give a false positive... Besides there are other hints which make me suspect a buffer overflow is really happening. > If neither DEBUG port option nor WITH_DEBUG make variable provide symbols > then file a bug. The DEBUG option is there and works (using base GDB had me think otherwise, but after switching to devel/gdb I can see debug info). However, ports seem to compile with -O2, which sometimes makes it hard to unterstand what's going on; so I added "CFLAGS= -O0" to Makefile. Putting that binary (with -O0) in production on one server has halted the stream of cores, at least for now: I had about one core per minute before; now it has been working fine for 30 minutes. The other server which shows this problem is not dumping cores right now. I'm not saying it's solved, however, since these dumps in the past have stopped appearing several times, and later started happening again; so I'll have to keep an eye on this. (My wild guess, but I'm not sure, is that this happens when a client needs to change its trust password: it tries again and again, and if it eventually succeeds, then I don't get any more core until another client needs this). > In addition to debug symbols try building with -fsanitize=address in > order to save time finding a place where the overflow occurs. I wanted to try this, but ended up with an error during "make configure": ---------------------------------------- Checking simple C program ==> #define CONFIG_H_IS_FROM_SAMBA 1 #define _SAMBA_BUILD_ 4 #define HAVE_CONFIG_H 1 #define SRCDIR "/usr/ports/net/samba48/work/samba-4.8.12" #define HAVE_SYS_UTSNAME_H 1 /* #undef SYSTEM_UNAME_SYSNAME */ /* #undef SYSTEM_UNAME_MACHINE */ /* #undef SYSTEM_UNAME_RELEASE */ /* #undef SYSTEM_UNAME_VERSION */ #define HAVE_STDIO_H 1 #include <stdio.h> int main(void) { printf("hello world"); return 0; } <== [1/2] Compiling test.c ['cc', '-O2', '-pipe', '-fsanitize=address', '-DLIBICONV_PLUG', '-fno-color-diagnostics', '-fstack-protector-strong', '-DLDAP_DEPRECATED', '-isystem', '/usr/local/include', '-fno-strict-aliasing', '-fno-omit-frame-pointer', '-I/usr/ports/net/samba48/work/samba-4.8.12/lib/replace/../../buildtools/wafsamba', '-MD', '-Idefault', '-I..', '-Idefault', '-I..', '-DLIBICONV_PLUG', '-isystem', '/usr/local/include', '-D_SAMBA_BUILD_=4', '-DHAVE_CONFIG_H=1', '../test.c', '-c', '-o', 'default/test_1.o'] [2/2] Linking default/testprog default/test_1.o: In function `asan.module_ctor': test.c:(.text+0x22): undefined reference to `__asan_init' test.c:(.text+0x27): undefined reference to `__asan_version_mismatch_check_v8' test.c:(.text+0x36): undefined reference to `__asan_register_globals' default/test_1.o: In function `asan.module_dtor': test.c:(.text+0x4c): undefined reference to `__asan_unregister_globals' cc: error: linker command failed with exit code 1 (use -v to see invocation) ['cc', 'default/test_1.o', '-o', '/usr/ports/net/samba48/work/samba-4.8.12/bin/.conf_check_0/testbuild/default/testprog', '-fstack-protector-strong', '-L/usr/local/lib'] bye & Thanks av.
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