thr3ads.net - Libguestfs - [Libguestfs] [PATCH nbdkit 2/3] configure: Add --disable-linker-script flag [Apr 2022]

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Richard W.M. Jones

2022-Apr-06 16:28 UTC

[Libguestfs] [PATCH nbdkit 1/3] configure: Report --enable-libfuzzer flag in summary output

This changes the summary output to report whether or not the
./configure --enable-libfuzzer flag was set:

    libfuzzer .............................. yes

or for --disable-libfuzzer / the default of not set:

    libfuzzer .............................. no
---
 configure.ac | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/configure.ac b/configure.ac
index 6a3be4ec..f86215d9 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1417,6 +1417,8 @@ echo "Optional server features:"
 echo
 feature "bash-completion ........................ " \
         test "x$HAVE_BASH_COMPLETION_TRUE" = "x"
+feature "libfuzzer .............................. " \
+        test "x$ENABLE_LIBFUZZER_TRUE" = "x"
 feature "manual pages ........................... " \
         test "x$HAVE_POD_TRUE" = "x"
 feature "SELinux ................................ " \
-- 
2.35.1

Richard W.M. Jones

2022-Apr-06 16:28 UTC

head link

[Libguestfs] [PATCH nbdkit 2/3] configure: Add --disable-linker-script flag

This flag allows you to disable the linker script (for the server
only).  This is necessary for ASAN to work as explained in the
documentation.

Thanks Eric Blake for helping me with working out the root cause.
---
 configure.ac       | 30 ++++++++++++++++++++++++------
 server/Makefile.am |  5 -----
 README             | 13 +++++++++++++
 3 files changed, 37 insertions(+), 11 deletions(-)

diff --git a/configure.ac b/configure.ac
index f86215d9..404d4e23 100644
--- a/configure.ac
+++ b/configure.ac
@@ -502,17 +502,19 @@ main (int argc, char *argv[])
     ])
 AM_CONDITIONAL([HAVE_ICONV], [test "x$iconv_working" =
"xyes"])
 
+use_linker_script_for_server=yes
+
 dnl Don't use linker script for the server on FreeBSD because
 dnl FreeBSD's linker is broken.  See eg:
 dnl https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=190851
-AC_MSG_CHECKING([if we should use a linker script for the server])
+AC_MSG_CHECKING([if we should disable the linker script (FreeBSD only)])
 AS_CASE([$host_os],
-  [freebsd*], [use_linker_script_for_server=no],
-  [use_linker_script_for_server=yes]
+  [freebsd*], [
+      use_linker_script_for_server=no
+      AC_MSG_RESULT([yes])
+  ],
+  [AC_MSG_RESULT([no])]
 )
-AC_MSG_RESULT([$use_linker_script_for_server])
-AM_CONDITIONAL([USE_LINKER_SCRIPT_FOR_SERVER],
-               [test "x$use_linker_script_for_server" =
"xyes"])
 
 dnl Check if -rdynamic linker flag works.
 acx_nbdkit_save_LDFLAGS="${LDFLAGS}"
@@ -691,9 +693,23 @@ AC_ARG_ENABLE([libfuzzer],
     [enable_libfuzzer=no])
 AS_IF([test "x$enable_libfuzzer" = "xyes"],[
     AC_DEFINE([ENABLE_LIBFUZZER],[1],[Enable special libFuzzer binary])
+    # We have to disable the linker script for libFuzzer because Clang
+    # adds loads of fuzzer and ASAN-related symbols that are required
+    # by the plugins but which our linker script tries to hide.
+    use_linker_script_for_server=no
 ])
 AM_CONDITIONAL([ENABLE_LIBFUZZER],[test "x$enable_libfuzzer" =
"xyes"])
 
+dnl Should we use the linker script with the server?  Note
+dnl some tests above may set this variable.
+AC_ARG_ENABLE([linker-script],
+    [AS_HELP_STRING([--disable-linker-script],
+                    [disable linker script for server (developers only)])],
+    [use_linker_script_for_server=$enableval],
+    [])
+AM_CONDITIONAL([USE_LINKER_SCRIPT_FOR_SERVER],
+               [test "x$use_linker_script_for_server" =
"xyes"])
+
 dnl Bash completion.
 PKG_CHECK_MODULES([BASH_COMPLETION], [bash-completion >= 2.0], [
     bash_completion=yes
@@ -1419,6 +1435,8 @@ feature "bash-completion ........................
" \
         test "x$HAVE_BASH_COMPLETION_TRUE" = "x"
 feature "libfuzzer .............................. " \
         test "x$ENABLE_LIBFUZZER_TRUE" = "x"
+feature "linker script .......................... " \
+        test "x$USE_LINKER_SCRIPT_FOR_SERVER_TRUE" = "x"
 feature "manual pages ........................... " \
         test "x$HAVE_POD_TRUE" = "x"
 feature "SELinux ................................ " \
diff --git a/server/Makefile.am b/server/Makefile.am
index 0039d1da..9ab621d5 100644
--- a/server/Makefile.am
+++ b/server/Makefile.am
@@ -108,13 +108,8 @@ nbdkit_LDFLAGS = \
 	$(NULL)
 EXTRA_nbdkit_DEPENDENCIES = nbdkit.syms
 if USE_LINKER_SCRIPT_FOR_SERVER
-# We have to disable the linker script for libFuzzer because Clang
-# adds loads of fuzzer and ASAN-related symbols that are required by
-# the plugins but which our linker script tries to hide.
-if !ENABLE_LIBFUZZER
 nbdkit_LDFLAGS += -Wl,--version-script=$(srcdir)/nbdkit.syms
 endif
-endif
 
 if IS_WINDOWS
 # On Windows, generate an import library so that plugins can link
diff --git a/README b/README
index 3480d561..7aa93b1d 100644
--- a/README
+++ b/README
@@ -324,6 +324,19 @@ For further information, see:
 https://libguestfs.org/
 https://github.com/NetworkBlockDevice/nbd/blob/master/doc/proto.md
 
+Address sanitizer (ASAN)
+------------------------
+
+You can compile nbdkit with clang and ASAN with:
+
+    ./configure CC=clang CXX=clang++ \
+                CFLAGS="-O0 -g -fsanitize=address
-fno-omit-frame-pointer" \
+                --disable-linker-script \
+                --disable-golang
+    make clean
+    make
+    ASAN_OPTIONS="allocator_may_return_null=1 detect_leaks=false"
make check
+
 Test coverage
 -------------
 
-- 
2.35.1

Richard W.M. Jones

2022-Apr-06 16:28 UTC

head link

[Libguestfs] [PATCH nbdkit 3/3] fuzzing: Recommend combining fuzzing with ASAN

ASAN (ie. Address Sanitizer or -fsanitize=address) adds extra checks
for out-of-bounds memory access, use-after-free and other memory
checks.  It's useful to combine this with fuzzing.

Fuzzing can normally only detect paths which cause the binary to
crash.  But some serious, latent bugs might not cause crashes (eg. a
rogue pointer overwrites another object in memory, but the other
object is not used or not used in a way that will cause a crash).
ASAN turns these kinds of bugs into crashes.

See also:
https://clang.llvm.org/docs/AddressSanitizer.html
https://aflplus.plus/docs/notes_for_asan/

Cherry picked from libnbd commit 43b1b95c981861c5c03cd563cf1b90e1f4c52cf8.
RWMJ: Some modifications were required for fuzzing to work with nbdkit.
---
 fuzzing/README | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/fuzzing/README b/fuzzing/README
index eeab9744..b2bc6f08 100644
--- a/fuzzing/README
+++ b/fuzzing/README
@@ -15,6 +15,7 @@ You will need to recompile nbdkit with AFL instrumentation:
 
 To use clang instead (recommended with AFL++):
 
+  export AFL_USE_ASAN=1
   ./configure CC=/usr/bin/afl-clang-lto CXX=/usr/bin/afl-clang-lto++
   make clean
   make
@@ -29,14 +30,16 @@ Master:
 
   mkdir -p fuzzing/sync_dir
   export AFL_PRELOAD=./plugins/memory/.libs/nbdkit-memory-plugin.so
-  afl-fuzz -i fuzzing/testcase_dir -o fuzzing/sync_dir -m 256 -M fuzz01 \
+  export ASAN_OPTIONS="allocator_may_return_null=1
detect_leaks=false"
+  afl-fuzz -i fuzzing/testcase_dir -o fuzzing/sync_dir -M fuzz01 \
       ./server/nbdkit -s -t 1 ./plugins/memory/.libs/nbdkit-memory-plugin.so 1M
 
 Slaves:
 
   # replace fuzzNN with fuzz02, fuzz03, etc.
   export AFL_PRELOAD=./plugins/memory/.libs/nbdkit-memory-plugin.so
-  afl-fuzz -i fuzzing/testcase_dir -o fuzzing/sync_dir -m 256 -S fuzzNN \
+  export ASAN_OPTIONS="allocator_may_return_null=1
detect_leaks=false"
+  afl-fuzz -i fuzzing/testcase_dir -o fuzzing/sync_dir -S fuzzNN \
       ./server/nbdkit -s -t 1 ./plugins/memory/.libs/nbdkit-memory-plugin.so 1M
 
 Test Coverage
-- 
2.35.1

Laszlo Ersek

2022-Apr-07 09:05 UTC

head link

[Libguestfs] [PATCH nbdkit 1/3] configure: Report --enable-libfuzzer flag in summary output

On 04/06/22 18:28, Richard W.M. Jones wrote:> This changes the summary output to report whether or not the
> ./configure --enable-libfuzzer flag was set:
> 
>     libfuzzer .............................. yes
> 
> or for --disable-libfuzzer / the default of not set:
> 
>     libfuzzer .............................. no
> ---
>  configure.ac | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/configure.ac b/configure.ac
> index 6a3be4ec..f86215d9 100644
> --- a/configure.ac
> +++ b/configure.ac
> @@ -1417,6 +1417,8 @@ echo "Optional server features:"
>  echo
>  feature "bash-completion ........................ " \
>          test "x$HAVE_BASH_COMPLETION_TRUE" = "x"
> +feature "libfuzzer .............................. " \
> +        test "x$ENABLE_LIBFUZZER_TRUE" = "x"
>  feature "manual pages ........................... " \
>          test "x$HAVE_POD_TRUE" = "x"
>  feature "SELinux ................................ " \
> 
Reviewed-by: Laszlo Ersek <lersek at redhat.com>

Libguestfs - Apr 2022 - [PATCH nbdkit 2/3] configure: Add --disable-linker-script flag

[Libguestfs] [PATCH nbdkit 1/3] configure: Report --enable-libfuzzer flag in summary output

[Libguestfs] [PATCH nbdkit 2/3] configure: Add --disable-linker-script flag

[Libguestfs] [PATCH nbdkit 3/3] fuzzing: Recommend combining fuzzing with ASAN

[Libguestfs] [PATCH nbdkit 1/3] configure: Report --enable-libfuzzer flag in summary output