blobmsg: blobmsg_parse and blobmsg_parse_array oob read fixes

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>

2 files changed, 0 insertions, 0 deletions

diff --git a/tests/fuzz/corpus/crash-a3585b70f1c7ffbdec10f6dadc964336118485c4 b/tests/fuzz/corpus/crash-a3585b70f1c7ffbdec10f6dadc964336118485c4
new file mode 100644
index 0000000..879ba4d
--- /dev/null
+++ b/tests/fuzz/corpus/crash-a3585b70f1c7ffbdec10f6dadc964336118485c4
diff --git a/tests/fuzz/corpus/crash-b3585b70f1c7ffbdec10f6dadc964336118485c4 b/tests/fuzz/corpus/crash-b3585b70f1c7ffbdec10f6dadc964336118485c4
new file mode 100644
index 0000000..12b832b
--- /dev/null
+++ b/tests/fuzz/corpus/crash-b3585b70f1c7ffbdec10f6dadc964336118485c4