linux-kernel - Re: [PATCH] crypto: ctr: avoid VLA use

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Message-ID: <201803152202.brqJ7obV%fengguang.wu@intel.com>
Date:   Thu, 15 Mar 2018 22:41:09 +0800
From:   kbuild test robot <lkp@...el.com>
To:     Salvatore Mesoraca <s.mesoraca16@...il.com>
Cc:     kbuild-all@...org, linux-kernel@...r.kernel.org,
        kernel-hardening@...ts.openwall.com, linux-crypto@...r.kernel.org,
        "David S. Miller" <davem@...emloft.net>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Kees Cook <keescook@...omium.org>,
        Salvatore Mesoraca <s.mesoraca16@...il.com>
Subject: Re: [PATCH] crypto: ctr: avoid VLA use

Hi Salvatore,

Thank you for the patch! Perhaps something to improve:

[auto build test WARNING on linus/master]
[also build test WARNING on v4.16-rc5 next-20180314]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]

url:    https://github.com/0day-ci/linux/commits/Salvatore-Mesoraca/crypto-ctr-avoid-VLA-use/20180315-213008
config: x86_64-randconfig-x014-201810 (attached as .config)
compiler: gcc-7 (Debian 7.3.0-1) 7.3.0
reproduce:
        # save the attached .config to linux build tree
        make ARCH=x86_64 

Note: it may well be a FALSE warning. FWIW you are at least aware of it now.
http://gcc.gnu.org/wiki/Better_Uninitialized_Warnings

All warnings (new ones prefixed by >>):

   crypto/ctr.c: In function 'crypto_ctr_crypt':
>> crypto/ctr.c:156:3: warning: 'tmp2' may be used uninitialized in this function [-Wmaybe-uninitialized]
      kfree(tmp2);
      ^~~~~~~~~~~
   crypto/ctr.c:133:18: note: 'tmp2' was declared here
     u8 *keystream, *tmp2;
                     ^~~~

vim +/tmp2 +156 crypto/ctr.c

   121	
   122	static int crypto_ctr_crypt_inplace(struct blkcipher_walk *walk,
   123					    struct crypto_cipher *tfm)
   124	{
   125		void (*fn)(struct crypto_tfm *, u8 *, const u8 *) =
   126			   crypto_cipher_alg(tfm)->cia_encrypt;
   127		unsigned int bsize = crypto_cipher_blocksize(tfm);
   128		unsigned long alignmask = crypto_cipher_alignmask(tfm);
   129		unsigned int nbytes = walk->nbytes;
   130		u8 *ctrblk = walk->iv;
   131		u8 *src = walk->src.virt.addr;
   132		DECLARE_CIPHER_BUFFER(tmp);
   133		u8 *keystream, *tmp2;
   134	
   135		if (CHECK_CIPHER_BUFFER(tmp, bsize, alignmask))
   136			keystream = tmp;
   137		else {
   138			tmp2 = kmalloc(bsize + alignmask, GFP_ATOMIC);
   139			if (!tmp2)
   140				return -ENOMEM;
   141			keystream = PTR_ALIGN(tmp2 + 0, alignmask + 1);
   142		}
   143	
   144		do {
   145			/* create keystream */
   146			fn(crypto_cipher_tfm(tfm), keystream, ctrblk);
   147			crypto_xor(src, keystream, bsize);
   148	
   149			/* increment counter in counterblock */
   150			crypto_inc(ctrblk, bsize);
   151	
   152			src += bsize;
   153		} while ((nbytes -= bsize) >= bsize);
   154	
   155		if (unlikely(keystream != tmp))
 > 156			kfree(tmp2);
   157		return nbytes;
   158	}
   159	

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