Re: [PATCH v2 1/2] crypto: Fix -Wstringop-truncation warnings

[Christophe LEROY]

Le 25/06/2018 à 14:45, Stafford Horne a écrit :
As of GCC 9.0.0 the build is reporting warnings like:

     crypto/ablkcipher.c: In function ‘crypto_ablkcipher_report’:
     crypto/ablkcipher.c:374:2: warning: ‘strncpy’ 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
explicitly performing '\0' termination.

Cc: Greg Kroah-Hartman <gre...@linuxfoundation.org>
Cc: Arnd Bergmann <a...@arndb.de>
Cc: Max Filippov <jcmvb...@gmail.com>
Cc: Eric Biggers <ebigge...@gmail.com>
Cc: Nick Desaulniers <nick.desaulni...@gmail.com>
Signed-off-by: Stafford Horne <sho...@gmail.com>
---
  crypto/ablkcipher.c | 2 ++
  crypto/blkcipher.c  | 1 +
  2 files changed, 3 insertions(+)

diff --git a/crypto/ablkcipher.c b/crypto/ablkcipher.c
index d880a4897159..1edb5000d783 100644
--- a/crypto/ablkcipher.c
+++ b/crypto/ablkcipher.c
@@ -373,6 +373,7 @@ 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));

Is it worth copying something we are going to discard at the following 
line ? Shouldn't you limit the copy to      sizeof(rblkcipher.geniv) - 1   ?

+       rblkcipher.geniv[sizeof(rblkcipher.geniv) - 1] = '\0';
  
  	rblkcipher.blocksize = alg->cra_blocksize;
        rblkcipher.min_keysize = alg->cra_ablkcipher.min_keysize;
@@ -447,6 +448,7 @@ 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));

Same comment here.

Christophe

+       rblkcipher.geniv[sizeof(rblkcipher.geniv) - 1] = '\0';
  
  	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..dd4dcab3766a 100644
--- a/crypto/blkcipher.c
+++ b/crypto/blkcipher.c
@@ -512,6 +512,7 @@ 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));
+       rblkcipher.geniv[sizeof(rblkcipher.geniv) - 1] = '\0';
  
  	rblkcipher.blocksize = alg->cra_blocksize;
        rblkcipher.min_keysize = alg->cra_blkcipher.min_keysize;