Merge tag 'keys-fixes-20200329' of git://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs

Pull keyrings fixes from David Howells:
 "Here's a couple of patches that fix a circular dependency between
  holding key->sem and mm->mmap_sem when reading data from a key.

  One potential issue is that a filesystem looking to use a key inside,
  say, ->readpages() could deadlock if the key being read is the key
  that's required and the buffer the key is being read into is on a page
  that needs to be fetched.

  The case actually detected is a bit more involved - with a filesystem
  calling request_key() and locking the target keyring for write - which
  could be being read"

* tag 'keys-fixes-20200329' of git://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs:
  KEYS: Avoid false positive ENOMEM error on key read
  KEYS: Don't write out to userspace while holding key semaphore

2 files changed, 10 insertions, 19 deletions

diff --git a/net/dns_resolver/dns_key.c b/net/dns_resolver/dns_key.c
index 3e1a90669006..ad53eb31d40f 100644
--- a/net/dns_resolver/dns_key.c
+++ b/net/dns_resolver/dns_key.c
@@ -302,7 +302,7 @@ static void dns_resolver_describe(const struct key *key, struct seq_file *m)
  * - the key's semaphore is read-locked
  */
 static long dns_resolver_read(const struct key *key,
-			      char __user *buffer, size_t buflen)
+			      char *buffer, size_t buflen)
 {
 	int err = PTR_ERR(key->payload.data[dns_key_error]);
 
diff --git a/net/rxrpc/key.c b/net/rxrpc/key.c
index 6c3f35fac42d..0c98313dd7a8 100644
--- a/net/rxrpc/key.c
+++ b/net/rxrpc/key.c
@@ -31,7 +31,7 @@ static void rxrpc_free_preparse_s(struct key_preparsed_payload *);
 static void rxrpc_destroy(struct key *);
 static void rxrpc_destroy_s(struct key *);
 static void rxrpc_describe(const struct key *, struct seq_file *);
-static long rxrpc_read(const struct key *, char __user *, size_t);
+static long rxrpc_read(const struct key *, char *, size_t);
 
 /*
  * rxrpc defined keys take an arbitrary string as the description and an
@@ -1042,12 +1042,12 @@ EXPORT_SYMBOL(rxrpc_get_null_key);
  * - this returns the result in XDR form
  */
 static long rxrpc_read(const struct key *key,
-		       char __user *buffer, size_t buflen)
+		       char *buffer, size_t buflen)
 {
 	const struct rxrpc_key_token *token;
 	const struct krb5_principal *princ;
 	size_t size;
-	__be32 __user *xdr, *oldxdr;
+	__be32 *xdr, *oldxdr;
 	u32 cnlen, toksize, ntoks, tok, zero;
 	u16 toksizes[AFSTOKEN_MAX];
 	int loop;
@@ -1124,30 +1124,25 @@ static long rxrpc_read(const struct key *key,
 	if (!buffer || buflen < size)
 		return size;
 
-	xdr = (__be32 __user *) buffer;
+	xdr = (__be32 *)buffer;
 	zero = 0;
 #define ENCODE(x)				\
 	do {					\
-		__be32 y = htonl(x);		\
-		if (put_user(y, xdr++) < 0)	\
-			goto fault;		\
+		*xdr++ = htonl(x);		\
 	} while(0)
 #define ENCODE_DATA(l, s)						\
 	do {								\
 		u32 _l = (l);						\
 		ENCODE(l);						\
-		if (copy_to_user(xdr, (s), _l) != 0)			\
-			goto fault;					\
-		if (_l & 3 &&						\
-		    copy_to_user((u8 __user *)xdr + _l, &zero, 4 - (_l & 3)) != 0) \
-			goto fault;					\
+		memcpy(xdr, (s), _l);					\
+		if (_l & 3)						\
+			memcpy((u8 *)xdr + _l, &zero, 4 - (_l & 3));	\
 		xdr += (_l + 3) >> 2;					\
 	} while(0)
 #define ENCODE64(x)					\
 	do {						\
 		__be64 y = cpu_to_be64(x);		\
-		if (copy_to_user(xdr, &y, 8) != 0)	\
-			goto fault;			\
+		memcpy(xdr, &y, 8);			\
 		xdr += 8 >> 2;				\
 	} while(0)
 #define ENCODE_STR(s)				\
@@ -1238,8 +1233,4 @@ static long rxrpc_read(const struct key *key,
 	ASSERTCMP((char __user *) xdr - buffer, ==, size);
 	_leave(" = %zu", size);
 	return size;
-
-fault:
-	_leave(" = -EFAULT");
-	return -EFAULT;
 }