Following regression was introduced in commit 5e75160f48 ("blobmsg:
fix attrs iteration in the blobmsg_check_array_len()"):
Thread 1 "test-fuzz" received signal SIGSEGV, Segmentation fault.
in blob_len (attr=0x6020000100d4) at libubox/blob.h:102
102 return (be32_to_cpu(attr->id_len) & BLOB_ATTR_LEN_MASK) - sizeof(struct blob_attr);
blob_len (attr=0x6020000100d4) at /libubox/blob.h:102
blob_raw_len (attr=0x6020000100d4) at /libubox/blob.h:111
blob_pad_len (attr=0x6020000100d4) at /libubox/blob.h:120
blobmsg_check_array_len (attr=0x6020000000d0, type=0, blob_len=10) at /libubox/blobmsg.c:145
fuzz_blobmsg_parse (data=0x6020000000d0 "\001\004", size=10) at /libubox/tests/fuzz/test-fuzz.c:57
Signed-off-by: Petr Štetiar <ynezz@true.cz>
Fix out of bounds read in blobmsg_parse and blobmsg_check_name. The
out of bounds read happens because blob_attr and blobmsg_hdr have
flexible array members, whose size is 0 in the corresponding sizeofs.
For example the __blob_for_each_attr macro checks whether rem >=
sizeof(struct blob_attr). However, what LibFuzzer discovered was,
if the input data was only 4 bytes, the data would be casted to blob_attr,
and later on blob_data(attr) would be called even though attr->data was empty.
The same issue could appear with data larger than 4 bytes, where data
wasn't empty, but contained only the start of the blobmsg_hdr struct,
and blobmsg_hdr name was empty. The bugs were discovered by fuzzing
blobmsg_parse and blobmsg_array_parse with LibFuzzer.
CC: Luka Perkov <luka.perkov@sartura.hr>
Reviewed-by: Jo-Philipp Wich <jo@mein.io>
Signed-off-by: Juraj Vijtiuk <juraj.vijtiuk@sartura.hr>
[refactored some checks, added fuzz inputs, adjusted unit test results]
Signed-off-by: Petr Štetiar <ynezz@true.cz>
Help detecting Valgrind OOB reads and other issues.
Conditional jump or move depends on uninitialised value(s)
at 0x5452886: blobmsg_parse (blobmsg.c:203)
by 0x400A8E: test_blobmsg (tests/test-blobmsg-parse.c:66)
by 0x400A8E: main (tests/test-blobmsg-parse.c:82)
Conditional jump or move depends on uninitialised value(s)
at 0x545247F: blobmsg_check_name (blobmsg.c:39)
by 0x545247F: blobmsg_check_attr_len (blobmsg.c:79)
by 0x5452710: blobmsg_parse_array (blobmsg.c:159)
by 0x400AB8: test_blobmsg (tests/test-blobmsg-parse.c:69)
by 0x400AB8: main (tests/test-blobmsg-parse.c:82)
Conditional jump or move depends on uninitialised value(s)
at 0x54524A0: blobmsg_check_name (blobmsg.c:42)
by 0x54524A0: blobmsg_check_attr_len (blobmsg.c:79)
by 0x5452710: blobmsg_parse_array (blobmsg.c:159)
by 0x400AB8: test_blobmsg (tests/test-blobmsg-parse.c:69)
by 0x400AB8: main (tests/test-blobmsg-parse.c:82)
Ref: http://lists.infradead.org/pipermail/openwrt-devel/2020-January/021204.html
Signed-off-by: Petr Štetiar <ynezz@true.cz>
==31775==ERROR: AddressSanitizer: SEGV on unknown address 0x604000a7c715
==31775==The signal is caused by a READ memory access.
#0 blobmsg_check_attr blobmsg.c:48:6
#1 blobmsg_parse_array blobmsg.c:118:8
#2 fuzz_blobmsg_parse test-blobmsg-parse-fuzzer.c:35:2
Signed-off-by: Petr Štetiar <ynezz@true.cz>
Found by fuzzer:
ERROR: AddressSanitizer: SEGV on unknown address 0x602100000455
The signal is caused by a READ memory access.
#0 in blob_check_type blob.c:214:43
#1 in blob_parse_attr blob.c:234:9
#2 in blob_parse_untrusted blob.c:272:12
#3 in fuzz_blob_parse tests/fuzzer/test-blob-parse-fuzzer.c:34:2
#4 in LLVMFuzzerTestOneInput tests/fuzzer/test-blob-parse-fuzzer.c:39:2
Caused by following line:
if (type == BLOB_ATTR_STRING && data[len - 1] != 0)
where len was pointing outside of the data buffer.
Signed-off-by: Petr Štetiar <ynezz@true.cz>
==5872==ERROR: AddressSanitizer: SEGV on unknown address 0x6020004100b4
==5872==The signal is caused by a READ memory access.
#0 blob_data blob.h
#1 blob_parse blob.c:228:2
Signed-off-by: Petr Štetiar <ynezz@true.cz>
LibFuzzer is in-process, coverage-guided, evolutionary fuzzing engine.
LibFuzzer is linked with the library under test, and feeds fuzzed inputs
to the library via a specific fuzzing entrypoint (aka "target
function"); the fuzzer then tracks which areas of the code are reached,
and generates mutations on the corpus of input data in order to maximize
the code coverage.
Lets use libFuzzer to fuzz blob and blobmsg parsing for the start.
Ref: https://llvm.org/docs/LibFuzzer.html
Signed-off-by: Petr Štetiar <ynezz@true.cz>
