[PATCH 4/5] smb: client: Clear sensitive stack data in smb1encrypt.c

[Thomas Huth <thuth@redhat.com>]

From: Thomas Huth <thuth@redhat.com>

Make sure to not leak signature data via the stack, clear it
with memzero_explicit() before leaving the function.

To avoid that we have to introduce "goto"-cleanup here, we re-arrange
the code a little bit (and drop the commented cifs_dump_mem debug
code that looks like a leftover from very early days).

Signed-off-by: Thomas Huth <thuth@redhat.com>
---
 fs/smb/client/smb1encrypt.c | 19 +++++++++----------
 1 file changed, 9 insertions(+), 10 deletions(-)

diff --git a/fs/smb/client/smb1encrypt.c b/fs/smb/client/smb1encrypt.c
index bf10fdeeedcab..c9eb68f04e7b0 100644
--- a/fs/smb/client/smb1encrypt.c
+++ b/fs/smb/client/smb1encrypt.c
@@ -81,6 +81,7 @@ int cifs_sign_rqst(struct smb_rqst *rqst, struct TCP_Server_Info *server,
 	else
 		memcpy(cifs_pdu->Signature.SecuritySignature, smb_signature, 8);
 
+	memzero_explicit(smb_signature, sizeof(smb_signature));
 	return rc;
 }
 
@@ -126,15 +127,13 @@ int cifs_verify_signature(struct smb_rqst *rqst,
 	rc = cifs_calc_signature(rqst, server, what_we_think_sig_should_be);
 	cifs_server_unlock(server);
 
-	if (rc)
-		return rc;
-
-/*	cifs_dump_mem("what we think it should be: ",
-		      what_we_think_sig_should_be, 16); */
-
-	if (crypto_memneq(server_response_sig, what_we_think_sig_should_be, 8))
-		return -EACCES;
-	else
-		return 0;
+	if (!rc) {
+		if (crypto_memneq(server_response_sig,
+				  what_we_think_sig_should_be, 8))
+			rc = -EACCES;
+	}
 
+	memzero_explicit(what_we_think_sig_should_be,
+			 sizeof(what_we_think_sig_should_be));
+	return rc;
 }
-- 
2.55.0