From 53de3b080d5eae31d0de219617155dcc34e7d698 Mon Sep 17 00:00:00 2001
From: Roberto Sassu <roberto.sassu@huawei.com>
Date: Mon, 27 Apr 2020 12:28:56 +0200
Subject: [PATCH] evm: Check also if *tfm is an error pointer in init_desc()
Git-commit: 53de3b080d5eae31d0de219617155dcc34e7d698
Patch-mainline: v5.7-rc7
References: bsc#1051510

This patch avoids a kernel panic due to accessing an error pointer set by
crypto_alloc_shash(). It occurs especially when there are many files that
require an unsupported algorithm, as it would increase the likelihood of
the following race condition:

Task A: *tfm = crypto_alloc_shash() <= error pointer
Task B: if (*tfm == NULL) <= *tfm is not NULL, use it
Task B: rc = crypto_shash_init(desc) <= panic
Task A: *tfm = NULL

This patch uses the IS_ERR_OR_NULL macro to determine whether or not a new
crypto context must be created.

Cc: stable@vger.kernel.org
Fixes: d46eb3699502b ("evm: crypto hash replaced by shash")
Co-developed-by: Krzysztof Struczynski <krzysztof.struczynski@huawei.com>
Signed-off-by: Krzysztof Struczynski <krzysztof.struczynski@huawei.com>
Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>
Acked-by: Takashi Iwai <tiwai@suse.de>

---
 security/integrity/evm/evm_crypto.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/security/integrity/evm/evm_crypto.c
+++ b/security/integrity/evm/evm_crypto.c
@@ -90,7 +90,7 @@ static struct shash_desc *init_desc(char
 		algo = evm_hash;
 	}
 
-	if (*tfm == NULL) {
+	if (IS_ERR_OR_NULL(*tfm)) {
 		mutex_lock(&mutex);
 		if (*tfm)
 			goto out;