[PATCH AUTOSEL 5.4 01/16] Revert "evm: Fix memleak in init_desc"

From: Sasha Levin
Date: Tue Jul 19 2022 - 21:26:02 EST


From: Xiu Jianfeng <xiujianfeng@xxxxxxxxxx>

[ Upstream commit 51dd64bb99e4478fc5280171acd8e1b529eadaf7 ]

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.

Reported-by: Guozihua (Scott) <guozihua@xxxxxxxxxx>
Signed-off-by: Xiu Jianfeng <xiujianfeng@xxxxxxxxxx>
Signed-off-by: Mimi Zohar <zohar@xxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
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 25dac691491b..ee6bd945f3d6 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);
}
--
2.35.1