Re: [RFC PATCH 1/2] crypto: Fix -Wstringop-truncation warnings

[Stafford Horne]

On Fri, Jun 22, 2018 at 07:41:49PM -0700, Eric Biggers wrote:
> On Sat, Jun 23, 2018 at 11:07:52AM +0900, Stafford Horne wrote:
> > As of GCC 9.0.0 the build is reporting warnings like:
> > 
> >     crypto/ablkcipher.c: In function âcrypto_ablkcipher_reportâ:
> >     crypto/ablkcipher.c:374:2: warning: âstrncpyâ specified bound 64 equals destination size [-Wstringop-truncation]
> >       strncpy(rblkcipher.geniv, alg->cra_ablkcipher.geniv ?: "<default>",
> >       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> >        sizeof(rblkcipher.geniv));
> >        ~~~~~~~~~~~~~~~~~~~~~~~~~
> > 
> > This means the strnycpy might create a non null terminated string.  Fix this by
> > limiting the size of the string copy to include the null terminator.
> > 
> > Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> > Cc: Arnd Bergmann <arnd@xxxxxxxx>
> > Signed-off-by: Stafford Horne <shorne@xxxxxxxxx>
> > ---
> >  crypto/ablkcipher.c | 4 ++--
> >  crypto/blkcipher.c  | 2 +-
> >  2 files changed, 3 insertions(+), 3 deletions(-)
> > 
> > diff --git a/crypto/ablkcipher.c b/crypto/ablkcipher.c
> > index d880a4897159..972cd7c879f6 100644
> > --- a/crypto/ablkcipher.c
> > +++ b/crypto/ablkcipher.c
> > @@ -372,7 +372,7 @@ static int crypto_ablkcipher_report(struct sk_buff *skb, struct crypto_alg *alg)
> >  
> >  	strncpy(rblkcipher.type, "ablkcipher", sizeof(rblkcipher.type));
> >  	strncpy(rblkcipher.geniv, alg->cra_ablkcipher.geniv ?: "<default>",
> > -		sizeof(rblkcipher.geniv));
> > +		sizeof(rblkcipher.geniv) - 1);
> >  
> >  	rblkcipher.blocksize = alg->cra_blocksize;
> >  	rblkcipher.min_keysize = alg->cra_ablkcipher.min_keysize;
> > @@ -446,7 +446,7 @@ static int crypto_givcipher_report(struct sk_buff *skb, struct crypto_alg *alg)
> >  
> >  	strncpy(rblkcipher.type, "givcipher", sizeof(rblkcipher.type));
> >  	strncpy(rblkcipher.geniv, alg->cra_ablkcipher.geniv ?: "<built-in>",
> > -		sizeof(rblkcipher.geniv));
> > +		sizeof(rblkcipher.geniv) - 1);
> >  
> >  	rblkcipher.blocksize = alg->cra_blocksize;
> >  	rblkcipher.min_keysize = alg->cra_ablkcipher.min_keysize;
> > diff --git a/crypto/blkcipher.c b/crypto/blkcipher.c
> > index 01c0d4aa2563..f1644b5cf68c 100644
> > --- a/crypto/blkcipher.c
> > +++ b/crypto/blkcipher.c
> > @@ -511,7 +511,7 @@ static int crypto_blkcipher_report(struct sk_buff *skb, struct crypto_alg *alg)
> >  
> >  	strncpy(rblkcipher.type, "blkcipher", sizeof(rblkcipher.type));
> >  	strncpy(rblkcipher.geniv, alg->cra_blkcipher.geniv ?: "<default>",
> > -		sizeof(rblkcipher.geniv));
> > +		sizeof(rblkcipher.geniv) - 1);
> >  
> >  	rblkcipher.blocksize = alg->cra_blocksize;
> >  	rblkcipher.min_keysize = alg->cra_blkcipher.min_keysize;
> 
> Your "fix" introduces an information disclosure bug, as it results in
> uninitialized memory being copied to userspace.  This same broken patch was sent
> by someone else too.
> 
> Maybe it would be best to just memset() the crypto_report_* structs to 0 after
> declaration and then replace the strncpy()'s with strscpy()'s, even if just to
> stop people from sending broken "fixes".  Do you want to do that?

Right, I didnt realize that we were using strncpy to also init the whole buffer.

I will do as suggest, and respic.

-Stafford