use SYS_PTRACE capability

[caolanm]

I'm finding that with e.g.

python infra/helper.py build_fuzzers libpng

all builds fail for me with...

configure:3443: checking whether we are cross compiling
configure:3451: clang -o conftest -g -fsanitize=address -fsanitize-coverage=edge,indirect-calls,8bit-counters conftest.c >&5
configure:3455: $? = 0
configure:3462: ./conftest
==1014==LeakSanitizer has encountered a fatal error.
==1014==HINT: For debugging, try setting environment variable LSAN_OPTIONS=verbosity=1:log_threads=1
==1014==HINT: LeakSanitizer does not work under ptrace (strace, gdb, etc)
configure:3466: $? = 1
configure:3473: error: in `/src/libpng':
configure:3475: error: cannot run C compiled programs.

with the defaults of...
CC=clang
CXX=clang++
CFLAGS=-g -fsanitize=address -fsanitize-coverage=edge,indirect-calls,8bit-counters
CXXFLAGS=-g -fsanitize=address -fsanitize-coverage=edge,indirect-calls,8bit-counters -stdlib=libc++

but adding --cap-add SYS_PTRACE makes it work

[inferno-chromium]

This could be fixed by #211. And also i don't see it locally (maybe rooted docker). I will let @mikea to review this.

[Dor1s]

+1, doesn't reproduce on my machine.
@caolanm, does python infra/helper.py build_image libpng work fine for you?

[caolanm]

@Dor1s yes, build_image libpng works fine, failure is just on running the first thing built with -fsanitize (docker is being run by root)

[Dor1s]

Thanks for clarification, @caolanm. I think your PR is good, since we add --cap-add SYS_PTRACE in

oss-fuzz/infra/libfuzzer-pipeline.groovy

Line 42 in 274fb85

def dockerRunOptions = "--user $dockerUid --cap-add SYS_PTRACE"

, but let's wait for @mikea for the final judgement :)