[llvm-dev] Segfault after compiling wget with dfsan

Sam Kerner via llvm-dev llvm-dev at lists.llvm.org
Mon Apr 6 08:41:41 PDT 2020

On Fri, Apr 3, 2020 at 7:54 PM Tianyi Chen via llvm-dev
<llvm-dev at lists.llvm.org> wrote:
> Hi all,
> I was trying to compile dfsan with wget. (Just enabling the dfsan feature, without actually making changes to the source code) Without dfsan, I am able to compile and run wget 1.19.5 (available at https://ftp.gnu.org/gnu/wget/wget-1.19.5.tar.gz). But when compiled with dfsan, it encountered a null pointer dereference error.
> Following an old post:http://lists.llvm.org/pipermail/cfe-dev/2014-May/037160.html . I was trying to use a blacklist for openssl functions.
> My commands are:
> export CC="clang -g -fsanitize=dataflow -fsanitize-blacklist=/tmp/openssl-list.txt
> export LDFLAGS=" -fsanitize=dataflow -fsanitize-blacklist=/tmp/openssl-list.txt
> ./configure --with-ssl=openssl
> make
> I've tried with clang 9,10, and the nightly build of 11 today.
> The error is:
> when trying to run "src/wget www.google.com"
> Program received signal SIGSEGV, Segmentation fault.
> 0x00005555556de113 in url_parse (url=0x555555c47550 "http://www.google.com",
>     error=0x7fffffffdb30, iri=0x555555c442f0 <dummy_iri>, percent_encode=true)
>     at url.c:837
> 837  if (*p == ':')
> and p is a null pointer.

If `p` is a null pointer, then reading *p should segfault.  To debug
this, you need to discover why p is null.

> I am not sure if this is because I misused the dfsan or for some other reason, any ideas?

Does this happen if you build without `-fsanitize=dataflow
-fsanitize-blacklist=/tmp/openssl-list.txt` in CC and LDFLAGS?

> Attached is the  fsanitize-blacklist I've used.
> Thanks,
> Tianyi
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