Re: Kernel panic - encryption/decryption failed when open file on Arm64

[xiakaixu]

Sorry for resend this email, just add the linux-crypto@xxxxxxxxxxxxxxx
and linux-kernel@xxxxxxxxxxxxxxxx


Hi,

Firstly, thanks for your reply!

To reproduce this kernel panic, I test the encryption/decryption feature 
on arm64 board with more memory. Just add the following
change:

    diff --git a/crypto/blkcipher.c b/crypto/blkcipher.c
    index 0122bec..10ef3f4 100644
    --- a/crypto/blkcipher.c
    +++ b/crypto/blkcipher.c
    @@ -240,6 +240,7 @@ static int blkcipher_walk_next(struct 
blkcipher_desc *desc,
                    walk->flags |= BLKCIPHER_WALK_COPY;
                    if (!walk->page) {
                            walk->page = (void 
*)__get_free_page(GFP_ATOMIC);
    +                      walk->page = NULL;
                            if (!walk->page)
                                    n = 0;
                    }


This change just set the walk->page to NULL manually.
I get the same crash when open file with the above change log. So I 
think this NULL page failure is not be handled correctly in current code.

Regards
Kaixu Xia

> On Thu, Sep 08, 2016 at 08:38:43PM +0800, xiakaixu wrote:
> > Hi,
> >
> > I am using the encryption/decryption feature on arm64 board and a kernel
> > panic occurs just when open a file.  As the memory size of the board
> > is limited
> > and there are some page allocation failures before the panic.
> >
> > Seems it is a kernel bug from the call trace log.
> >
> >      ...
> >      - fscrypt_get_encryption_info
> >        - get_crypt_info.part.1
> >         - validate_user_key.isra.0
> >          - derive_aes_gcm_key
> >           - crypto_gcm_decrypt
> >            - ablk_decrypt
> >             - ctr_encrypt
> >              - blkcipher_walk_done
> >                - blkcipher_walk_next
> >                 -  __get_free_pages
> > ----------------------------------> page allocation failure
> >        ...
> >             - aes_ctr_encrypt
> > -----------------------------------------> the input parameter is
> > NULL pointer as the page allocation failure
> >
> >
> > The input parameter of function aes_ctr_encrypt() comes from the
> > /struct blkcipher_walk//
> > //walk/, and this variable /walk /is allocated by the function
> > __get_free_pages(). So if this
> > page allocate failed, the input parameter of function
> > aes_ctr_encrypt() will be NULL. The
> > panic will occurs if we don't check the input parameter.
> >
> > Not sure about this and wish to get your opinions!
>
> If the page allocation fails in blkcipher_walk_next it'll simply
> switch over to processing it block by block. so I don't think the
> warning is related to the crash.
>
> Cheers,