> From: owner-linux-security-module@xxxxxxxxxxxxxxx [mailto:owner-linux- > security-module@xxxxxxxxxxxxxxx] On Behalf Of Dan Carpenter > Sent: Tuesday, May 12, 2020 2:34 PM > 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. static inline bool __must_check IS_ERR_OR_NULL(__force const void *ptr) { return unlikely(!ptr) || IS_ERR_VALUE((unsigned long)ptr); } CPU#1 CPU#2 *tfm = crypto_alloc_shash(algo, 0, CRYPTO_NOLOAD); unlikely(!ptr) *tfm = NULL; IS_ERR_VALUE((unsigned long)ptr); desc = kmalloc(sizeof(*desc) + crypto_shash_descsize(*tfm), Could this happen? Roberto HUAWEI TECHNOLOGIES Duesseldorf GmbH, HRB 56063 Managing Director: Li Peng, Li Jian, Shi Yanli
