stable request: mips strncpy is broken

stable request: mips strncpy is broken

[Florian Westphal]

Hello,

Please consider queueing

commit 3c0be5849259b729580c23549330973a2dd513a2
Author: Paul Burton <paulburton@kernel.org>
 MIPS: Drop 32-bit asm string functions

The commit is part of 5.5-rc1.

We got a bug report about following nftables rule not matching
even if it should on Linux 5.4.y mips32:

  meta iifname "br-vlan"

'iifname' uses strncpy(..., IFNAMSIZ) to copy dev->name to the register.
The MIPS asm function doesn't zero-pad the remaining bytes, but that is
needed for the compare op to work reliably.

The reporter confirmed that this removal fixes the issue, the generic C
version behaves as expected.

The patch doesn't apply cleanly to 5.4, there is a minor conflict
related to FORTIFY macro, but its easily resolved as all code
is removed.

I did not try earlier 4.4.y releases but I susepct they should also get
this patch applied.

I can send a 5.4.y backport if thats preferred.

Thanks.

Re: stable request: mips strncpy is broken

[Greg KH]

On Wed, Mar 03, 2021 at 06:23:36PM +0100, Florian Westphal wrote:
> Hello,
> 
> Please consider queueing
> 
> commit 3c0be5849259b729580c23549330973a2dd513a2
> Author: Paul Burton <paulburton@kernel.org>
>  MIPS: Drop 32-bit asm string functions
> 
> The commit is part of 5.5-rc1.
> 
> We got a bug report about following nftables rule not matching
> even if it should on Linux 5.4.y mips32:
> 
>   meta iifname "br-vlan"
> 
> 'iifname' uses strncpy(..., IFNAMSIZ) to copy dev->name to the register.
> The MIPS asm function doesn't zero-pad the remaining bytes, but that is
> needed for the compare op to work reliably.
> 
> The reporter confirmed that this removal fixes the issue, the generic C
> version behaves as expected.
> 
> The patch doesn't apply cleanly to 5.4, there is a minor conflict
> related to FORTIFY macro, but its easily resolved as all code
> is removed.
> 
> I did not try earlier 4.4.y releases but I susepct they should also get
> this patch applied.
> 
> I can send a 5.4.y backport if thats preferred.

Please do, that way I know it is done correctly and has been tested.

And here I thought no one was actually using MIPS anymore :)

thanks,

greg k-h

Re: stable request: mips strncpy is broken

[Florian Westphal]

Greg KH <gregkh@linuxfoundation.org> wrote:
> > I did not try earlier 4.4.y releases but I susepct they should also get
> > this patch applied.
> > 
> > I can send a 5.4.y backport if thats preferred.
> 
> Please do, that way I know it is done correctly and has been tested.

Will do, but note that I can't test this.