Re: Stable backport request: skbuff: Proactively round up to kmalloc bucket size

[Greg Kroah-Hartman]

On Mon, May 22, 2023 at 12:23:50PM -0600, Daniel Díaz wrote:
> Hello!
> 
> Would the stable maintainers please consider backporting the following
> commit to the 6.1? We are trying to build gki_defconfig (plus a few
> extras) on Arm64 and test it under Qemu-arm64, but it fails to boot.
> Bisection has pointed here.

I do not see a "gki_defconfig" in the kernel tree, is this just
out-of-tree stuff?

If so, why not just add this to your out-of-tree stuff?

> We have verified that cherry-picking this patch on top of v6.1.29
> applies cleanly and allows the kernel to boot.

So what is breaking that requires this to fix the problem?  What is the
problem?

> 
> commit 12d6c1d3a2ad0c199ec57c201cdc71e8e157a232
> Author: Kees Cook <keescook@xxxxxxxxxxxx>
> Date:   Tue Oct 25 15:39:35 2022 -0700
> 
>     skbuff: Proactively round up to kmalloc bucket size
> 
>     Instead of discovering the kmalloc bucket size _after_ allocation, round
>     up proactively so the allocation is explicitly made for the full size,
>     allowing the compiler to correctly reason about the resulting size of
>     the buffer through the existing __alloc_size() hint.
> 
>     This will allow for kernels built with CONFIG_UBSAN_BOUNDS or the
>     coming dynamic bounds checking under CONFIG_FORTIFY_SOURCE to gain
>     back the __alloc_size() hints that were temporarily reverted in commit
>     93dd04ab0b2b ("slab: remove __alloc_size attribute from
> __kmalloc_track_caller")
> 
>     Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
>     Cc: Eric Dumazet <edumazet@xxxxxxxxxx>
>     Cc: Jakub Kicinski <kuba@xxxxxxxxxx>
>     Cc: Paolo Abeni <pabeni@xxxxxxxxxx>
>     Cc: netdev@xxxxxxxxxxxxxxx
>     Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
>     Cc: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
>     Cc: David Rientjes <rientjes@xxxxxxxxxx>
>     Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
>     Link: https://patchwork.kernel.org/project/netdevbpf/patch/20221021234713.you.031-kees@xxxxxxxxxx/
>     Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
>     Link: https://lore.kernel.org/r/20221025223811.up.360-kees@xxxxxxxxxx
>     Signed-off-by: Paolo Abeni <pabeni@xxxxxxxxxx>

This feels like a new feature, why would a 6.1.y system need it?  What
commit id does it fix?

thanks,

greg k-h