Re: [PATCH nft] netlink: fix stack buffer overrun when emitting ranged expressions

[Florian Westphal <fw@strlen.de>]

Pablo Neira Ayuso <pablo@netfilter.org> wrote:
> Hi Florian,
> 
> On Fri, Mar 14, 2025 at 01:41:49PM +0100, Florian Westphal wrote:
> > Included bogon input generates following Sanitizer splat:
> > 
> > AddressSanitizer: dynamic-stack-buffer-overflow on address 0x7...
> > WRITE of size 2 at 0x7fffffffcbe4 thread T0
> >     #0 0x0000003a68b8 in __asan_memset (src/nft+0x3a68b8) (BuildId: 3678ff51a5405c77e3e0492b9a985910efee73b8)
> >     #1 0x0000004eb603 in __mpz_export_data src/gmputil.c:108:2
> >     #2 0x0000004eb603 in netlink_export_pad src/netlink.c:256:2
> >     #3 0x0000004eb603 in netlink_gen_range src/netlink.c:471:2
> >     #4 0x0000004ea250 in __netlink_gen_data src/netlink.c:523:10
> >     #5 0x0000004e8ee3 in alloc_nftnl_setelem src/netlink.c:205:3
> >     #6 0x0000004d4541 in mnl_nft_setelem_batch src/mnl.c:1816:11
> > 
> > Problem is that the range end is emitted to the buffer at the *padded*
> > location (rounded up to next register size), but buffer sizing is
> > based of the expression length, not the padded length.
> > 
> > Also extend the test script: Capture stderr and if we see
> > AddressSanitizer warning, make it fail.
> > 
> > Same bug as the one fixed in 600b84631410 ("netlink: fix stack buffer overflow with sub-reg sized prefixes"),
> > just in a different function.
> > 
> > Apply same fix: no dynamic array + add a length check.
> 
> While at it, extend it for similar code too until there is a way to
> consolidate this? See attachment.

Sure, I can merge your snippet and push it out, is that okay?