Hello Roberto Sassu,
The patch 53de3b080d5e: "evm: Check also if *tfm is an error pointer
in init_desc()" from Apr 27, 2020, leads to the following static
checker warning:
security/integrity/evm/evm_crypto.c:119 init_desc()
error: '*tfm' dereferencing possible ERR_PTR()
security/integrity/evm/evm_crypto.c
89
90 tfm = &evm_tfm[hash_algo];
91 algo = hash_algo_name[hash_algo];
92 }
93
94 if (IS_ERR_OR_NULL(*tfm)) {
This used to be a "if (!*tfm)" check.
95 mutex_lock(&mutex);
96 if (*tfm)
97 goto out;
Then we test again with the lock held. But in the new code if "*tfm"
is an error pointer then we jump directly to the unlock and crash on the
next line. I can't see how the commit would fix anything.
98 *tfm = crypto_alloc_shash(algo, 0, CRYPTO_NOLOAD);
99 if (IS_ERR(*tfm)) {
100 rc = PTR_ERR(*tfm);
101 pr_err("Can not allocate %s (reason: %ld)\n", algo, rc);
102 *tfm = NULL;
103 mutex_unlock(&mutex);
104 return ERR_PTR(rc);
105 }
106 if (type == EVM_XATTR_HMAC) {
107 rc = crypto_shash_setkey(*tfm, evmkey, evmkey_len);
108 if (rc) {
109 crypto_free_shash(*tfm);
110 *tfm = NULL;
111 mutex_unlock(&mutex);
112 return ERR_PTR(rc);
113 }
114 }
115 out:
116 mutex_unlock(&mutex);
117 }
118
119 desc = kmalloc(sizeof(*desc) + crypto_shash_descsize(*tfm),
^^^^
I don't understand how using *tfm outside of a lock is safe at all
anyway.
120 GFP_KERNEL);
121 if (!desc)
122 return ERR_PTR(-ENOMEM);
123
regards,
dan carpenter
