hastd: Fix nv data size check

[des]

Summary

The data size check, as currently written, can be defeated by providing
a very large number that rounds up to 0, which will pass the check
(because zero plus the size of the header and name is smaller than the
size of the message) but cause a segfault later when used to index the
data array.

Rewrite the data size check to take rounding into account, and add a
cast to ensure the name size can't round up to zero.

MFC after: 1 week
PR: 266827

[markj]

sbin/hastd/nv.c

250–251

Isn't it still possible to have roundup2(dsize, 8) < size - NVH_HSIZE(nvh) even if the newly added check passes? Will that cause problems when ptr and size are adjusted at the end of the loop?

[des]

sbin/hastd/nv.c

250–251

You're right, if dsize is smaller than size - NVH_SIZE(nvh) but rounds up to something larger, then size ends up wrapping around.

[des]

better

[markj]

I think this patch fixes the problem at hand, but see the inline comment.

sbin/hastd/nv.c

231

NVH_HSIZE() also has a problem if roundup2(nvh->nvh_namesize, 8) == 0, I think.

[des]

sbin/hastd/nv.c

231

I'm tempted to just put a hard limit of INT_MAX on both nvh_namesize and nvh_dsize...

231

that won't be enough on 32-bit platforms though :(

[des]

namesize