Bug Report: Unaligned Access in BGP Code on ARMv7 Platforms

[Ondrej Zajicek]

On Tue, Dec 10, 2024 at 09:15:46PM +0100, nick via Bird-users wrote:
> I also uploaded the coredumpfile:
> https://github.com/PolynomialDivision/coredumpupload/blob/main/bird_coredump

Thanks. This seems like an interesting issue. In BIRD, generic net_addr
structure is explicitly u64-aligned (to accomodate VPN variants), while
specific net_addr_ip4 and net_addr_ip6 are just u32-aligned. In this case
net_addr_ip6 is allocated with u32 alignment, but then copied with
net_copy(), which assumes generic net_addr for arguments, and compiler
probably used some u64-optimized copying, which required 64-bit alignment
despite being on 32-bit platform,

For starters, try the attached patch. But it is preliminary, we will revisit
alignment of these structures.


> > > > The root cause appears to be insufficient alignment of memory
> > > > allocated for
> > > > structures, specifically in this line:
> > > > 
> > > > ```c
> > > > px = mb_alloc(c->pool, sizeof(struct bgp_prefix) + net->length);
> > > > ```

Note that it is really allocated two lines above, here:

  px = sl_alloc(c->prefix_slab);

-- 
Elen sila lumenn' omentielvo

Ondrej 'Santiago' Zajicek (email: santiago at crfreenet.org)
"To err is human -- to blame it on a computer is even more so."
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