[PATCH v2 1/2] evm: Alloc evm_digest in evm_verify_hmac() if CONFIG_VMAP_STACK=y

From: Roberto Sassu
Date: Thu Dec 01 2022 - 05:07:11 EST


From: Roberto Sassu <roberto.sassu@xxxxxxxxxx>

Commit ac4e97abce9b8 ("scatterlist: sg_set_buf() argument must be in linear
mapping") checks that both the signature and the digest reside in the
linear mapping area.

However, more recently commit ba14a194a434c ("fork: Add generic vmalloced
stack support"), made it possible to move the stack in the vmalloc area,
which is not contiguous, and thus not suitable for sg_set_buf() which needs
adjacent pages.

Fix this by checking if CONFIG_VMAP_STACK is enabled. If yes, allocate an
evm_digest structure, and use that instead of the in-stack counterpart.

Cc: stable@xxxxxxxxxxxxxxx # 4.9.x
Fixes: ba14a194a434 ("fork: Add generic vmalloced stack support")
Signed-off-by: Roberto Sassu <roberto.sassu@xxxxxxxxxx>
---
security/integrity/evm/evm_main.c | 26 +++++++++++++++++++++-----
1 file changed, 21 insertions(+), 5 deletions(-)

diff --git a/security/integrity/evm/evm_main.c b/security/integrity/evm/evm_main.c
index 23d484e05e6f..7f76d6103f2e 100644
--- a/security/integrity/evm/evm_main.c
+++ b/security/integrity/evm/evm_main.c
@@ -174,6 +174,7 @@ static enum integrity_status evm_verify_hmac(struct dentry *dentry,
struct signature_v2_hdr *hdr;
enum integrity_status evm_status = INTEGRITY_PASS;
struct evm_digest digest;
+ struct evm_digest *digest_ptr = &digest;
struct inode *inode;
int rc, xattr_len, evm_immutable = 0;

@@ -231,14 +232,26 @@ static enum integrity_status evm_verify_hmac(struct dentry *dentry,
}

hdr = (struct signature_v2_hdr *)xattr_data;
- digest.hdr.algo = hdr->hash_algo;
+
+ if (IS_ENABLED(CONFIG_VMAP_STACK)) {
+ digest_ptr = kmalloc(sizeof(*digest_ptr), GFP_NOFS);
+ if (!digest_ptr) {
+ rc = -ENOMEM;
+ break;
+ }
+ }
+
+ digest_ptr->hdr.algo = hdr->hash_algo;
+
rc = evm_calc_hash(dentry, xattr_name, xattr_value,
- xattr_value_len, xattr_data->type, &digest);
+ xattr_value_len, xattr_data->type,
+ digest_ptr);
if (rc)
break;
rc = integrity_digsig_verify(INTEGRITY_KEYRING_EVM,
(const char *)xattr_data, xattr_len,
- digest.digest, digest.hdr.length);
+ digest_ptr->digest,
+ digest_ptr->hdr.length);
if (!rc) {
inode = d_backing_inode(dentry);

@@ -268,8 +281,11 @@ static enum integrity_status evm_verify_hmac(struct dentry *dentry,
else
evm_status = INTEGRITY_FAIL;
}
- pr_debug("digest: (%d) [%*phN]\n", digest.hdr.length, digest.hdr.length,
- digest.digest);
+ pr_debug("digest: (%d) [%*phN]\n", digest_ptr->hdr.length,
+ digest_ptr->hdr.length, digest_ptr->digest);
+
+ if (digest_ptr && digest_ptr != &digest)
+ kfree(digest_ptr);
out:
if (iint)
iint->evm_status = evm_status;
--
2.25.1