[PATCH v2] ecryptfs: validate auth tok payload size

[Adriano Cordova <adrianox@gmail.com>]

Validate that a key payload is large enough to hold a struct
ecryptfs_auth_tok, and that the password token's
session_key_encryption_key_bytes fits within
session_key_encryption_key[], before the payload is dereferenced.

Cc: <stable@vger.kernel.org>
Reported-by: syzbot+03c68e42ce4b33f7ce9b@syzkaller.appspotmail.com
Reported-by: Nguyen Duy Nhat Anh <neganhat@gmail.com>
Tested-by: syzbot+03c68e42ce4b33f7ce9b@syzkaller.appspotmail.com
Link: https://syzkaller.appspot.com/bug?extid=03c68e42ce4b33f7ce9b
Signed-off-by: Adriano Cordova <adrianox@gmail.com>
---
Changes in v2:
- Add Reported-by tag.

 fs/ecryptfs/ecryptfs_kernel.h | 6 ++++++
 fs/ecryptfs/keystore.c        | 7 +++++++
 2 files changed, 13 insertions(+)

diff --git a/fs/ecryptfs/ecryptfs_kernel.h b/fs/ecryptfs/ecryptfs_kernel.h
index 58165928ed1e..4315c18ba1cd 100644
--- a/fs/ecryptfs/ecryptfs_kernel.h
+++ b/fs/ecryptfs/ecryptfs_kernel.h
@@ -88,6 +88,9 @@ ecryptfs_get_encrypted_key_payload_data(struct key *key)
 	if (!payload)
 		return ERR_PTR(-EKEYREVOKED);
 
+	if (payload->payload_datalen < sizeof(struct ecryptfs_auth_tok))
+		return ERR_PTR(-EINVAL);
+
 	return (struct ecryptfs_auth_tok *)payload->payload_data;
 }
 
@@ -124,6 +127,9 @@ ecryptfs_get_key_payload_data(struct key *key)
 	if (!ukp)
 		return ERR_PTR(-EKEYREVOKED);
 
+	if (ukp->datalen < sizeof(struct ecryptfs_auth_tok))
+		return ERR_PTR(-EINVAL);
+
 	return (struct ecryptfs_auth_tok *)ukp->data;
 }
 
diff --git a/fs/ecryptfs/keystore.c b/fs/ecryptfs/keystore.c
index 51651314b7a6..7f2dbc81fcbc 100644
--- a/fs/ecryptfs/keystore.c
+++ b/fs/ecryptfs/keystore.c
@@ -477,6 +477,13 @@ ecryptfs_verify_auth_tok_from_key(struct key *auth_tok_key,
 		rc = -EINVAL;
 		goto out;
 	}
+	if ((*auth_tok)->token_type == ECRYPTFS_PASSWORD
+	    && (*auth_tok)->token.password.session_key_encryption_key_bytes
+	       > ECRYPTFS_MAX_KEY_BYTES) {
+		printk(KERN_ERR "Invalid password auth_tok sKEK size\n");
+		rc = -EINVAL;
+		goto out;
+	}
 out:
 	return rc;
 }
-- 
2.51.0