Merge branch 'net-start-to-replace-copy_from_sockptr'

Eric Dumazet says:

====================
net: start to replace copy_from_sockptr()

We got several syzbot reports about unsafe copy_from_sockptr()
calls. After fixing some of them, it appears that we could
use a new helper to factorize all the checks in one place.

This series targets net tree, we can later start converting
many call sites in net-next.
====================

Link: https://lore.kernel.org/r/20240408082845.3957374-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

3 files changed, 36 insertions, 11 deletions

diff --git a/drivers/isdn/mISDN/socket.c b/drivers/isdn/mISDN/socket.c
index 2776ca5fc33f..b215b28cad7b 100644
--- a/drivers/isdn/mISDN/socket.c
+++ b/drivers/isdn/mISDN/socket.c
@@ -401,23 +401,23 @@ data_sock_ioctl(struct socket *sock, unsigned int cmd, unsigned long arg)
 }
 
 static int data_sock_setsockopt(struct socket *sock, int level, int optname,
-				sockptr_t optval, unsigned int len)
+				sockptr_t optval, unsigned int optlen)
 {
 	struct sock *sk = sock->sk;
 	int err = 0, opt = 0;
 
 	if (*debug & DEBUG_SOCKET)
 		printk(KERN_DEBUG "%s(%p, %d, %x, optval, %d)\n", __func__, sock,
-		       level, optname, len);
+		       level, optname, optlen);
 
 	lock_sock(sk);
 
 	switch (optname) {
 	case MISDN_TIME_STAMP:
-		if (copy_from_sockptr(&opt, optval, sizeof(int))) {
-			err = -EFAULT;
+		err = copy_safe_from_sockptr(&opt, sizeof(opt),
+					     optval, optlen);
+		if (err)
 			break;
-		}
 
 		if (opt)
 			_pms(sk)->cmask |= MISDN_TIME_STAMP;
diff --git a/include/linux/sockptr.h b/include/linux/sockptr.h
index 307961b41541..317200cd3a60 100644
--- a/include/linux/sockptr.h
+++ b/include/linux/sockptr.h
@@ -50,11 +50,36 @@ static inline int copy_from_sockptr_offset(void *dst, sockptr_t src,
 	return 0;
 }
 
+/* Deprecated.
+ * This is unsafe, unless caller checked user provided optlen.
+ * Prefer copy_safe_from_sockptr() instead.
+ */
 static inline int copy_from_sockptr(void *dst, sockptr_t src, size_t size)
 {
 	return copy_from_sockptr_offset(dst, src, 0, size);
 }
 
+/**
+ * copy_safe_from_sockptr: copy a struct from sockptr
+ * @dst:   Destination address, in kernel space. This buffer must be @ksize
+ *         bytes long.
+ * @ksize: Size of @dst struct.
+ * @optval: Source address. (in user or kernel space)
+ * @optlen: Size of @optval data.
+ *
+ * Returns:
+ *  * -EINVAL: @optlen < @ksize
+ *  * -EFAULT: access to userspace failed.
+ *  * 0 : @ksize bytes were copied
+ */
+static inline int copy_safe_from_sockptr(void *dst, size_t ksize,
+					 sockptr_t optval, unsigned int optlen)
+{
+	if (optlen < ksize)
+		return -EINVAL;
+	return copy_from_sockptr(dst, optval, ksize);
+}
+
 static inline int copy_struct_from_sockptr(void *dst, size_t ksize,
 		sockptr_t src, size_t usize)
 {
diff --git a/net/nfc/llcp_sock.c b/net/nfc/llcp_sock.c
index 819157bbb5a2..d5344563e525 100644
--- a/net/nfc/llcp_sock.c
+++ b/net/nfc/llcp_sock.c
@@ -252,10 +252,10 @@ static int nfc_llcp_setsockopt(struct socket *sock, int level, int optname,
 			break;
 		}
 
-		if (copy_from_sockptr(&opt, optval, sizeof(u32))) {
-			err = -EFAULT;
+		err = copy_safe_from_sockptr(&opt, sizeof(opt),
+					     optval, optlen);
+		if (err)
 			break;
-		}
 
 		if (opt > LLCP_MAX_RW) {
 			err = -EINVAL;
@@ -274,10 +274,10 @@ static int nfc_llcp_setsockopt(struct socket *sock, int level, int optname,
 			break;
 		}
 
-		if (copy_from_sockptr(&opt, optval, sizeof(u32))) {
-			err = -EFAULT;
+		err = copy_safe_from_sockptr(&opt, sizeof(opt),
+					     optval, optlen);
+		if (err)
 			break;
-		}
 
 		if (opt > LLCP_MAX_MIUX) {
 			err = -EINVAL;