[PATCH 1/5] smb: client: Clear sensitive stack data in smb2transport.c

[Thomas Huth <thuth@redhat.com>]

From: Thomas Huth <thuth@redhat.com>

Sensitive data like keys that are stored in stack-local arrays could
be leaked via the stack to the calling functions. There is no known
vulnerability for this right now, but it's good security style to
explicitly zeroize this sensitive material as soon as possible to
avoid that it could be exploited together with other bugs later.

Signed-off-by: Thomas Huth <thuth@redhat.com>
---
 fs/smb/client/smb2transport.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/fs/smb/client/smb2transport.c b/fs/smb/client/smb2transport.c
index 1143ee52470a7..fdc634d99da03 100644
--- a/fs/smb/client/smb2transport.c
+++ b/fs/smb/client/smb2transport.c
@@ -249,6 +249,8 @@ smb2_calc_signature(struct smb_rqst *rqst, struct TCP_Server_Info *server)
 	if (!rc)
 		memcpy(shdr->Signature, smb2_signature, SMB2_SIGNATURE_SIZE);
 
+	memzero_explicit(key, sizeof(key));
+	memzero_explicit(&hmac_ctx, sizeof(hmac_ctx));
 	return rc;
 }
 
@@ -283,6 +285,7 @@ static void generate_key(struct cifs_ses *ses, struct kvec label,
 	hmac_sha256_final(&hmac_ctx, prfhash);
 
 	memcpy(key, prfhash, key_size);
+	memzero_explicit(prfhash, sizeof(prfhash));
 }
 
 struct derivation {
@@ -482,6 +485,7 @@ smb3_calc_signature(struct smb_rqst *rqst, struct TCP_Server_Info *server)
 	memset(shdr->Signature, 0x0, SMB2_SIGNATURE_SIZE);
 
 	rc = aes_cmac_preparekey(&cmac_key, key, SMB2_CMACAES_SIZE);
+	memzero_explicit(key, sizeof(key));
 	if (rc) {
 		cifs_server_dbg(VFS, "%s: Could not set key for cmac aes\n", __func__);
 		return rc;
-- 
2.55.0