From b17af3e503a5861ae1437254a8a2a3600e768cc4 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Zbigniew=20J=C4=99drzejewski-Szmek?= Date: Mon, 22 Jun 2020 17:09:49 +0200 Subject: [PATCH] bus-message: avoid dereferencing a NULL pointer We'd try to map a zero-byte buffer from a NULL pointer, which is undefined behaviour. src/systemd/src/libsystemd/sd-bus/bus-message.c:3161:60: runtime error: applying zero offset to null pointer #0 0x7f6ff064e691 in find_part /work/build/../../src/systemd/src/libsystemd/sd-bus/bus-message.c:3161:60 #1 0x7f6ff0640788 in message_peek_body /work/build/../../src/systemd/src/libsystemd/sd-bus/bus-message.c:3283:16 #2 0x7f6ff064e8db in enter_struct_or_dict_entry /work/build/../../src/systemd/src/libsystemd/sd-bus/bus-message.c:3967:21 #3 0x7f6ff06444ac in bus_message_enter_struct /work/build/../../src/systemd/src/libsystemd/sd-bus/bus-message.c:4009:13 #4 0x7f6ff0641dde in sd_bus_message_enter_container /work/build/../../src/systemd/src/libsystemd/sd-bus/bus-message.c:4136:21 #5 0x7f6ff0619874 in sd_bus_message_dump /work/build/../../src/systemd/src/libsystemd/sd-bus/bus-dump.c:178:29 #6 0x4293d9 in LLVMFuzzerTestOneInput /work/build/../../src/systemd/src/fuzz/fuzz-bus-message.c:39:9 #7 0x441986 in fuzzer::Fuzzer::ExecuteCallback(unsigned char const*, unsigned long) /src/libfuzzer/FuzzerLoop.cpp:558:15 #8 0x44121e in fuzzer::Fuzzer::RunOne(unsigned char const*, unsigned long, bool, fuzzer::InputInfo*, bool*) /src/libfuzzer/FuzzerLoop.cpp:470:3 #9 0x443164 in fuzzer::Fuzzer::ReadAndExecuteSeedCorpora(std::__1::vector >&) /src/libfuzzer/FuzzerLoop.cpp:770:7 #10 0x4434bc in fuzzer::Fuzzer::Loop(std::__1::vector >&) /src/libfuzzer/FuzzerLoop.cpp:799:3 #11 0x42d2bc in fuzzer::FuzzerDriver(int*, char***, int (*)(unsigned char const*, unsigned long)) /src/libfuzzer/FuzzerDriver.cpp:846:6 #12 0x42978a in main /src/libfuzzer/FuzzerMain.cpp:19:10 #13 0x7f6fef13c82f in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x2082f) #14 0x407808 in _start (out/fuzz-bus-message+0x407808) --- src/libsystemd/sd-bus/bus-message.c | 3 ++- .../fuzz-bus-message/zero-offset-to-null-pointer | Bin 0 -> 64 bytes 2 files changed, 2 insertions(+), 1 deletion(-) create mode 100644 test/fuzz/fuzz-bus-message/zero-offset-to-null-pointer diff --git a/src/libsystemd/sd-bus/bus-message.c b/src/libsystemd/sd-bus/bus-message.c index 4005023d241..8a8fbde7810 100644 --- a/src/libsystemd/sd-bus/bus-message.c +++ b/src/libsystemd/sd-bus/bus-message.c @@ -3159,7 +3159,8 @@ static struct bus_body_part* find_part(sd_bus_message *m, size_t index, size_t s return NULL; if (p) - *p = (uint8_t*) part->data + index - begin; + *p = part->data ? (uint8_t*) part->data + index - begin + : NULL; /* Avoid dereferencing a NULL pointer. */ m->cached_rindex_part = part; m->cached_rindex_part_begin = begin; diff --git a/test/fuzz/fuzz-bus-message/zero-offset-to-null-pointer b/test/fuzz/fuzz-bus-message/zero-offset-to-null-pointer new file mode 100644 index 0000000000000000000000000000000000000000..c1380441ed1a85b8e37d11453effdb7f9f4fd4d1 GIT binary patch literal 64 zcmc~16k%ilf{d(u23;V{!I;jVuAxzpr&*d&S(sQ-TA`Uzkpu>bKoZIX^D{vD0P6P< AZU6uP literal 0 HcmV?d00001