On Thu, Dec 01, 2022 at 11:06:24AM +0100, Roberto Sassu wrote:
> 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);
What is the actual problem here? Where is a scatterlist being created from this
buffer? AFAICS it never happens.
- Eric
