netdev - [PATCH 4/4] net: improve the user pointer check in init_user

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Date:   Tue, 28 Jul 2020 18:38:36 +0200
From:   Christoph Hellwig <hch@....de>
To:     "David S. Miller" <davem@...emloft.net>
Cc:     Jan Engelhardt <jengelh@...i.de>, Ido Schimmel <idosch@...sch.org>,
        "Jason A. Donenfeld" <Jason@...c4.com>,
        David Laight <David.Laight@...LAB.COM>, netdev@...r.kernel.org
Subject: [PATCH 4/4] net: improve the user pointer check in init_user_sockptr

Make sure not just the pointer itself but the whole range lies in
the user address space.  For that pass the length and then use
the access_ok helper to do the check.

Fixes: 6d04fe15f78a ("net: optimize the sockptr_t for unified kernel/user address spaces")
Reported-by: David Laight <David.Laight@...LAB.COM>
Signed-off-by: Christoph Hellwig <hch@....de>
---
 include/linux/sockptr.h     | 18 ++++++------------
 net/ipv4/bpfilter/sockopt.c |  2 +-
 net/socket.c                |  2 +-
 3 files changed, 8 insertions(+), 14 deletions(-)

diff --git a/include/linux/sockptr.h b/include/linux/sockptr.h
index 9e6c81d474cba8..96840def9d69cc 100644
--- a/include/linux/sockptr.h
+++ b/include/linux/sockptr.h
@@ -27,14 +27,6 @@ static inline sockptr_t KERNEL_SOCKPTR(void *p)
 {
 	return (sockptr_t) { .kernel = p };
 }
-
-static inline int __must_check init_user_sockptr(sockptr_t *sp, void __user *p)
-{
-	if ((unsigned long)p >= TASK_SIZE)
-		return -EFAULT;
-	sp->user = p;
-	return 0;
-}
 #else /* CONFIG_ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE */
 typedef struct {
 	union {
@@ -53,14 +45,16 @@ static inline sockptr_t KERNEL_SOCKPTR(void *p)
 {
 	return (sockptr_t) { .kernel = p, .is_kernel = true };
 }
+#endif /* CONFIG_ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE */
 
-static inline int __must_check init_user_sockptr(sockptr_t *sp, void __user *p)
+static inline int __must_check init_user_sockptr(sockptr_t *sp, void __user *p,
+		size_t size)
 {
-	sp->user = p;
-	sp->is_kernel = false;
+	if (!access_ok(p, size))
+		return -EFAULT;
+	*sp = (sockptr_t) { .user = p };
 	return 0;
 }
-#endif /* CONFIG_ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE */
 
 static inline bool sockptr_is_null(sockptr_t sockptr)
 {
diff --git a/net/ipv4/bpfilter/sockopt.c b/net/ipv4/bpfilter/sockopt.c
index 94f18d2352d007..545b2640f0194d 100644
--- a/net/ipv4/bpfilter/sockopt.c
+++ b/net/ipv4/bpfilter/sockopt.c
@@ -65,7 +65,7 @@ int bpfilter_ip_get_sockopt(struct sock *sk, int optname,
 
 	if (get_user(len, optlen))
 		return -EFAULT;
-	err = init_user_sockptr(&optval, user_optval);
+	err = init_user_sockptr(&optval, user_optval, len);
 	if (err)
 		return err;
 	return bpfilter_mbox_request(sk, optname, optval, len, false);
diff --git a/net/socket.c b/net/socket.c
index 94ca4547cd7c53..aff52e81653ce3 100644
--- a/net/socket.c
+++ b/net/socket.c
@@ -2105,7 +2105,7 @@ int __sys_setsockopt(int fd, int level, int optname, char __user *user_optval,
 	if (optlen < 0)
 		return -EINVAL;
 
-	err = init_user_sockptr(&optval, user_optval);
+	err = init_user_sockptr(&optval, user_optval, optlen);
 	if (err)
 		return err;
 
-- 
2.27.0