[linux-next:master 10444/12404] security/keys/trusted-keys/trusted_tpm2.c:38:25: warning: Either the condition '!scratch' is redundant or there is pointer arithmetic with NULL pointer. [nullPointerArithmeticRedundantCheck]

[kernel test robot <rong.a.chen@intel.com>]

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git master
head:   dcf1b51d6b2ac5da234ae6883ed0e9422c339588
commit: 14676f1eb79660b6ee262644fa788a5c42ac19e4 [10444/12404] security: keys: trusted: use ASN.1 TPM2 key format for the blobs
compiler: hppa64-linux-gcc (GCC) 9.3.0

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@intel.com>


cppcheck possible warnings: (new ones prefixed by >>, may not real problems)

>> security/keys/trusted-keys/trusted_tpm2.c:38:25: warning: Either the condition '!scratch' is redundant or there is pointer arithmetic with NULL pointer. [nullPointerArithmeticRedundantCheck]
    u8 *end_work = scratch + SCRATCH_SIZE;
                           ^
   security/keys/trusted-keys/trusted_tpm2.c:50:6: note: Assuming that condition '!scratch' is not redundant
    if (!scratch)
        ^
   security/keys/trusted-keys/trusted_tpm2.c:38:25: note: Null pointer addition
    u8 *end_work = scratch + SCRATCH_SIZE;
                           ^

vim +38 security/keys/trusted-keys/trusted_tpm2.c

14676f1eb79660 James Bottomley 2021-01-27  30  
14676f1eb79660 James Bottomley 2021-01-27  31  static int tpm2_key_encode(struct trusted_key_payload *payload,
14676f1eb79660 James Bottomley 2021-01-27  32  			   struct trusted_key_options *options,
14676f1eb79660 James Bottomley 2021-01-27  33  			   u8 *src, u32 len)
14676f1eb79660 James Bottomley 2021-01-27  34  {
14676f1eb79660 James Bottomley 2021-01-27  35  	const int SCRATCH_SIZE = PAGE_SIZE;
14676f1eb79660 James Bottomley 2021-01-27  36  	u8 *scratch = kmalloc(SCRATCH_SIZE, GFP_KERNEL);
14676f1eb79660 James Bottomley 2021-01-27  37  	u8 *work = scratch, *work1;
14676f1eb79660 James Bottomley 2021-01-27 @38  	u8 *end_work = scratch + SCRATCH_SIZE;
14676f1eb79660 James Bottomley 2021-01-27  39  	u8 *priv, *pub;
14676f1eb79660 James Bottomley 2021-01-27  40  	u16 priv_len, pub_len;
14676f1eb79660 James Bottomley 2021-01-27  41  
14676f1eb79660 James Bottomley 2021-01-27  42  	priv_len = get_unaligned_be16(src) + 2;
14676f1eb79660 James Bottomley 2021-01-27  43  	priv = src;
14676f1eb79660 James Bottomley 2021-01-27  44  
14676f1eb79660 James Bottomley 2021-01-27  45  	src += priv_len;
14676f1eb79660 James Bottomley 2021-01-27  46  
14676f1eb79660 James Bottomley 2021-01-27  47  	pub_len = get_unaligned_be16(src) + 2;
14676f1eb79660 James Bottomley 2021-01-27  48  	pub = src;
14676f1eb79660 James Bottomley 2021-01-27  49  
14676f1eb79660 James Bottomley 2021-01-27  50  	if (!scratch)
14676f1eb79660 James Bottomley 2021-01-27  51  		return -ENOMEM;
14676f1eb79660 James Bottomley 2021-01-27  52  
14676f1eb79660 James Bottomley 2021-01-27  53  	work = asn1_encode_oid(work, end_work, tpm2key_oid,
14676f1eb79660 James Bottomley 2021-01-27  54  			       asn1_oid_len(tpm2key_oid));
14676f1eb79660 James Bottomley 2021-01-27  55  
14676f1eb79660 James Bottomley 2021-01-27  56  	if (options->blobauth_len == 0) {
14676f1eb79660 James Bottomley 2021-01-27  57  		unsigned char bool[3], *w = bool;
14676f1eb79660 James Bottomley 2021-01-27  58  		/* tag 0 is emptyAuth */
14676f1eb79660 James Bottomley 2021-01-27  59  		w = asn1_encode_boolean(w, w + sizeof(bool), true);
14676f1eb79660 James Bottomley 2021-01-27  60  		if (WARN(IS_ERR(w), "BUG: Boolean failed to encode"))
14676f1eb79660 James Bottomley 2021-01-27  61  			return PTR_ERR(w);
14676f1eb79660 James Bottomley 2021-01-27  62  		work = asn1_encode_tag(work, end_work, 0, bool, w - bool);
14676f1eb79660 James Bottomley 2021-01-27  63  	}
14676f1eb79660 James Bottomley 2021-01-27  64  
14676f1eb79660 James Bottomley 2021-01-27  65  	/*
14676f1eb79660 James Bottomley 2021-01-27  66  	 * Assume both octet strings will encode to a 2 byte definite length
14676f1eb79660 James Bottomley 2021-01-27  67  	 *
14676f1eb79660 James Bottomley 2021-01-27  68  	 * Note: For a well behaved TPM, this warning should never
14676f1eb79660 James Bottomley 2021-01-27  69  	 * trigger, so if it does there's something nefarious going on
14676f1eb79660 James Bottomley 2021-01-27  70  	 */
14676f1eb79660 James Bottomley 2021-01-27  71  	if (WARN(work - scratch + pub_len + priv_len + 14 > SCRATCH_SIZE,
14676f1eb79660 James Bottomley 2021-01-27  72  		 "BUG: scratch buffer is too small"))
14676f1eb79660 James Bottomley 2021-01-27  73  		return -EINVAL;
14676f1eb79660 James Bottomley 2021-01-27  74  
14676f1eb79660 James Bottomley 2021-01-27  75  	work = asn1_encode_integer(work, end_work, options->keyhandle);
14676f1eb79660 James Bottomley 2021-01-27  76  	work = asn1_encode_octet_string(work, end_work, pub, pub_len);
14676f1eb79660 James Bottomley 2021-01-27  77  	work = asn1_encode_octet_string(work, end_work, priv, priv_len);
14676f1eb79660 James Bottomley 2021-01-27  78  
14676f1eb79660 James Bottomley 2021-01-27  79  	work1 = payload->blob;
14676f1eb79660 James Bottomley 2021-01-27  80  	work1 = asn1_encode_sequence(work1, work1 + sizeof(payload->blob),
14676f1eb79660 James Bottomley 2021-01-27  81  				     scratch, work - scratch);
14676f1eb79660 James Bottomley 2021-01-27  82  	if (WARN(IS_ERR(work1), "BUG: ASN.1 encoder failed"))
14676f1eb79660 James Bottomley 2021-01-27  83  		return PTR_ERR(work1);
14676f1eb79660 James Bottomley 2021-01-27  84  
14676f1eb79660 James Bottomley 2021-01-27  85  	return work1 - payload->blob;
14676f1eb79660 James Bottomley 2021-01-27  86  }
14676f1eb79660 James Bottomley 2021-01-27  87  

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