mm: add kvfree_sensitive() for freeing sensitive data objects

For kvmalloc'ed data object that contains sensitive information like
cryptographic keys, we need to make sure that the buffer is always cleared
before freeing it.  Using memset() alone for buffer clearing may not
provide certainty as the compiler may compile it away.  To be sure, the
special memzero_explicit() has to be used.

This patch introduces a new kvfree_sensitive() for freeing those sensitive
data objects allocated by kvmalloc().  The relevant places where
kvfree_sensitive() can be used are modified to use it.

Fixes: 4f0882491a14 ("KEYS: Avoid false positive ENOMEM error on key read")
Suggested-by: Linus Torvalds <[email protected]>
Signed-off-by: Waiman Long <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Reviewed-by: Eric Biggers <[email protected]>
Acked-by: David Howells <[email protected]>
Cc: Jarkko Sakkinen <[email protected]>
Cc: James Morris <[email protected]>
Cc: "Serge E. Hallyn" <[email protected]>
Cc: Joe Perches <[email protected]>
Cc: Matthew Wilcox <[email protected]>
Cc: David Rientjes <[email protected]>
Cc: Uladzislau Rezki <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Linus Torvalds <[email protected]>

2 files changed, 5 insertions, 22 deletions

diff --git a/security/keys/internal.h b/security/keys/internal.h
index 6d0ca48ae9a5..153d35c20d3d 100644
--- a/security/keys/internal.h
+++ b/security/keys/internal.h
@@ -350,15 +350,4 @@ static inline void key_check(const struct key *key)
 #define key_check(key) do {} while(0)
 
 #endif
-
-/*
- * Helper function to clear and free a kvmalloc'ed memory object.
- */
-static inline void __kvzfree(const void *addr, size_t len)
-{
-	if (addr) {
-		memset((void *)addr, 0, len);
-		kvfree(addr);
-	}
-}
 #endif /* _INTERNAL_H */
diff --git a/security/keys/keyctl.c b/security/keys/keyctl.c
index 5e01192e222a..edde63a63007 100644
--- a/security/keys/keyctl.c
+++ b/security/keys/keyctl.c
@@ -142,10 +142,7 @@ SYSCALL_DEFINE5(add_key, const char __user *, _type,
 
 	key_ref_put(keyring_ref);
  error3:
-	if (payload) {
-		memzero_explicit(payload, plen);
-		kvfree(payload);
-	}
+	kvfree_sensitive(payload, plen);
  error2:
 	kfree(description);
  error:
@@ -360,7 +357,7 @@ long keyctl_update_key(key_serial_t id,
 
 	key_ref_put(key_ref);
 error2:
-	__kvzfree(payload, plen);
+	kvfree_sensitive(payload, plen);
 error:
 	return ret;
 }
@@ -914,7 +911,7 @@ can_read_key:
 		 */
 		if (ret > key_data_len) {
 			if (unlikely(key_data))
-				__kvzfree(key_data, key_data_len);
+				kvfree_sensitive(key_data, key_data_len);
 			key_data_len = ret;
 			continue;	/* Allocate buffer */
 		}
@@ -923,7 +920,7 @@ can_read_key:
 			ret = -EFAULT;
 		break;
 	}
-	__kvzfree(key_data, key_data_len);
+	kvfree_sensitive(key_data, key_data_len);
 
 key_put_out:
 	key_put(key);
@@ -1225,10 +1222,7 @@ long keyctl_instantiate_key_common(key_serial_t id,
 		keyctl_change_reqkey_auth(NULL);
 
 error2:
-	if (payload) {
-		memzero_explicit(payload, plen);
-		kvfree(payload);
-	}
+	kvfree_sensitive(payload, plen);
 error:
 	return ret;
 }