On Tue, May 12, 2020 at 11:31:53AM +0000, Roberto Sassu wrote: > > 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; No. I was wrong. > > > 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. > Actually by the time we take the lock then *tfm is either valid or NULL so this code works. It's confusing though. regards, dan carpenter
