> From: Dan Carpenter [mailto:dan.carpenter@xxxxxxxxxx] > Sent: Tuesday, May 12, 2020 12:48 PM > > 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. Hello Dan you are right. The fix should be applied in both places. if (!IS_ERR_OR_NULL(*tfm)) goto out; > 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. I think the purpose of the mutex is just to prevent two concurrent allocations. Later, it should not be a problem, as *tfm is never freed. Thanks Roberto HUAWEI TECHNOLOGIES Duesseldorf GmbH, HRB 56063 Managing Director: Li Peng, Li Jian, Shi Yanli > 120 GFP_KERNEL); > 121 if (!desc) > 122 return ERR_PTR(-ENOMEM); > 123 > > regards, > dan carpenter
