linux-kernel - [PATCH -next] Revert "evm: Fix memleak in init

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Message-ID: <20220527111726.195825-1-xiujianfeng@huawei.com>
Date:   Fri, 27 May 2022 19:17:26 +0800
From:   Xiu Jianfeng <xiujianfeng@...wei.com>
To:     <zohar@...ux.ibm.com>, <dmitry.kasatkin@...il.com>,
        <jmorris@...ei.org>, <serge@...lyn.com>
CC:     <linux-integrity@...r.kernel.org>,
        <linux-security-module@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: [PATCH -next] Revert "evm: Fix memleak in init_desc"

This reverts commit ccf11dbaa07b328fa469415c362d33459c140a37.

Commit ccf11dbaa07b ("evm: Fix memleak in init_desc") said there is
memleak in init_desc. That may be incorrect, as we can see, tmp_tfm is
saved in one of the two global variables hmac_tfm or evm_tfm[hash_algo],
then if init_desc is called next time, there is no need to alloc tfm
again, so in the error path of kmalloc desc or crypto_shash_init(desc),
It is not a problem without freeing tmp_tfm.

And also that commit did not reset the global variable to NULL after
freeing tmp_tfm and this makes *tfm a dangling pointer which may cause a
UAF issue.

Signed-off-by: Xiu Jianfeng <xiujianfeng@...wei.com>
---
 security/integrity/evm/evm_crypto.c | 7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

diff --git a/security/integrity/evm/evm_crypto.c b/security/integrity/evm/evm_crypto.c
index a733aff02006..708de9656bbd 100644
--- a/security/integrity/evm/evm_crypto.c
+++ b/security/integrity/evm/evm_crypto.c
@@ -75,7 +75,7 @@ static struct shash_desc *init_desc(char type, uint8_t hash_algo)
 {
 	long rc;
 	const char *algo;
-	struct crypto_shash **tfm, *tmp_tfm = NULL;
+	struct crypto_shash **tfm, *tmp_tfm;
 	struct shash_desc *desc;
 
 	if (type == EVM_XATTR_HMAC) {
@@ -120,16 +120,13 @@ static struct shash_desc *init_desc(char type, uint8_t hash_algo)
 alloc:
 	desc = kmalloc(sizeof(*desc) + crypto_shash_descsize(*tfm),
 			GFP_KERNEL);
-	if (!desc) {
-		crypto_free_shash(tmp_tfm);
+	if (!desc)
 		return ERR_PTR(-ENOMEM);
-	}
 
 	desc->tfm = *tfm;
 
 	rc = crypto_shash_init(desc);
 	if (rc) {
-		crypto_free_shash(tmp_tfm);
 		kfree(desc);
 		return ERR_PTR(rc);
 	}
-- 
2.17.1