Re: UBSAN: object-size-mismatch in wg_xmit

On Mon, Jan 11, 2021 at 12:58 PM Dmitry Vyukov [off-list ref] wrote:

On Mon, Jan 11, 2021 at 6:35 PM Jeffrey Walton [off-list ref] wrote:

quoted

On Mon, Jan 11, 2021 at 12:20 PM Dmitry Vyukov [off-list ref] wrote:

quoted

...
FTR, I've disabled the following UBSAN configs:
UBSAN_MISC
UBSAN_DIV_ZERO
UBSAN_BOOL
UBSAN_OBJECT_SIZE
UBSAN_SIGNED_OVERFLOW
UBSAN_UNSIGNED_OVERFLOW
UBSAN_ENUM
UBSAN_ALIGNMENT
UBSAN_UNREACHABLE

Only these are enabled now:
UBSAN_BOUNDS
UBSAN_SHIFT

This is commit:
https://github.com/google/syzkaller/commit/2c1f2513486f21d26b1942ce77ffc782677fbf4e

I think the commit cut too deep.

The overflows are important if folks are building with compilers other than GCC.

The aligned data accesses are important on platforms like MIPS64 and Sparc64.

Object size is important because it catches destination buffer overflows.

I don't know what's in miscellaneous. There may be something useful in there.

Hi Jeff,

See the commit for reasons why each of these is disabled.
E.g. object size, somebody first needs to fix bugs like this one.
While things like skbuff have these UBs on trivial workloads, there is
no point in involving fuzzing and making it crash on this trivial bug
all the time and stopping doing any other kernel testing as the
result.

Going off-topic a bit, what would you suggest for UBSAN_OBJECT_SIZE?

It seems to me object size checking is being conflated with object
type. It seems to me they need to be split: UBSAN_OBJECT_SIZE for
actual object sizes, and UBSAN_OBJECT_TYPE for the casts.

I still have a bitter taste in my mouth from
https://www.cvedetails.com/bugtraq-bid/57602/libupnp-Multiple-Buffer-Overflow-Vulnerabilities.html.
I hate to see buffer checks go away. (And I realize the kernel folks
are more skilled than the guy who wrote libupnp).

Jeff