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smb: client: Compare MACs in constant time

PATCH New Eric Biggers 1 participant 1 message Mar 10

Subsystems (4)
Stable branch Crypto API SMB client (CIFS) Kernel SMB3 server (ksmbd)
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Eric Biggers

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PATCH 1/1 smb: client: Compare MACs in constant time

commit 26bc83b88bbbf054f0980a4a42047a8d1e210e4c upstream.

To prevent timing attacks, MAC comparisons need to be constant-time. Replace the memcmp() with the correct function, crypto_memneq().

Fixes 1da177e4c3f4 ("Linux-2.6.12-rc2")
Cc [email protected]
Acked-by Paulo Alcantara (Red Hat) <[email protected]>
Signed-off-by Eric Biggers <[email protected]>
Signed-off-by Steve French <[email protected]>
---
 fs/cifs/cifsencrypt.c   | 3 ++-
 fs/cifs/smb2transport.c | 4 +++-
 2 files changed, 5 insertions(+), 2 deletions(-)
fs/cifs/cifsencrypt.c +2 -1
index 9daa256f69d41..96cbfebbb6483 100644
@@ -34,10 +34,11 @@
 #include <linux/random.h>
 #include <linux/highmem.h>
 #include <linux/fips.h>
 #include <crypto/arc4.h>
 #include <crypto/aead.h>
+#include <crypto/algapi.h>
 
 int __cifs_calc_signature(struct smb_rqst *rqst,
 			struct TCP_Server_Info *server, char *signature,
 			struct shash_desc *shash)
 {

@@ -253,11 +254,11 @@ int cifs_verify_signature(struct smb_rqst *rqst,
 		return rc;
 
 /*	cifs_dump_mem("what we think it should be: ",
 		      what_we_think_sig_should_be, 16); */
 
-	if (memcmp(server_response_sig, what_we_think_sig_should_be, 8))
+	if (crypto_memneq(server_response_sig, what_we_think_sig_should_be, 8))
 		return -EACCES;
 	else
 		return 0;
 
 }
fs/cifs/smb2transport.c +3 -1
index adb324234b444..c02e57d8e228b 100644
@@ -29,10 +29,11 @@
 #include <linux/delay.h>
 #include <linux/uaccess.h>
 #include <asm/processor.h>
 #include <linux/mempool.h>
 #include <linux/highmem.h>
+#include <crypto/algapi.h>
 #include <crypto/aead.h>
 #include "smb2pdu.h"
 #include "cifsglob.h"
 #include "cifsproto.h"
 #include "smb2proto.h"

@@ -685,11 +686,12 @@ smb2_verify_signature(struct smb_rqst *rqst, struct TCP_Server_Info *server)
 	rc = server->ops->calc_signature(rqst, server, true);
 
 	if (rc)
 		return rc;
 
-	if (memcmp(server_response_sig, shdr->Signature, SMB2_SIGNATURE_SIZE)) {
+	if (crypto_memneq(server_response_sig, shdr->Signature,
+			  SMB2_SIGNATURE_SIZE)) {
 		cifs_dbg(VFS, "sign fail cmd 0x%x message id 0x%llx\n",
 			shdr->Command, shdr->MessageId);
 		return -EACCES;
 	} else
 		return 0;

base-commit: aed5c3b77cd53ba74f66767b03bfb9177662af4b

Signature · 1 line
2.53.0