[Devel] [PATCH RHEL7 COMMIT] ms/socketpair(): allocate descriptors first

[Vasily Averin]

The commit is pushed to "branch-rh7-3.10.0-1160.6.1.vz7.171.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh7-3.10.0-1160.6.1.vz7.171.1
------>
commit 0561af703e11627ebe91dac9123e2c7569448500
Author: Al Viro <viro at ZenIV.linux.org.uk>
Date:   Thu Dec 3 12:31:19 2020 +0300

    ms/socketpair(): allocate descriptors first
    
    simplifies failure exits considerably...
    
    Reviewed-by: Eric Dumazet <edumazet at google.com>
    Signed-off-by: Al Viro <viro at zeniv.linux.org.uk>
    Signed-off-by: David S. Miller <davem at davemloft.net>
    
    (cherry-picked from commit 016a266bdfeda268afb2228b6217fd4771334635)
    https://syzkaller.appspot.com/bug?id=23d0799f98b7c8c4bc3f5ecff7c28a87c64e40e8
    https://jira.sw.ru/browse/PSBM-123046
    Signed-off-by: Vasily Averin <vvs at virtuozzo.com>
---
 net/socket.c | 89 ++++++++++++++++++++++++++----------------------------------
 1 file changed, 38 insertions(+), 51 deletions(-)

diff --git a/net/socket.c b/net/socket.c
index dd8fa2d..6ea6b18 100644
--- a/net/socket.c
+++ b/net/socket.c
@@ -1512,87 +1512,74 @@ SYSCALL_DEFINE4(socketpair, int, family, int, type, int, protocol,
 		flags = (flags & ~SOCK_NONBLOCK) | O_NONBLOCK;
 
 	/*
+	 * reserve descriptors and make sure we won't fail
+	 * to return them to userland.
+	 */
+	fd1 = get_unused_fd_flags(flags);
+	if (unlikely(fd1 < 0))
+		return fd1;
+
+	fd2 = get_unused_fd_flags(flags);
+	if (unlikely(fd2 < 0)) {
+		put_unused_fd(fd1);
+		return fd2;
+	}
+
+	err = put_user(fd1, &usockvec[0]);
+	if (err)
+		goto out;
+
+	err = put_user(fd2, &usockvec[1]);
+	if (err)
+		goto out;
+
+	/*
 	 * Obtain the first socket and check if the underlying protocol
 	 * supports the socketpair call.
 	 */
 
 	err = sock_create(family, type, protocol, &sock1);
-	if (err < 0)
+	if (unlikely(err < 0))
 		goto out;
 
 	err = sock_create(family, type, protocol, &sock2);
-	if (err < 0)
-		goto out_release_1;
-
-	err = sock1->ops->socketpair(sock1, sock2);
-	if (err < 0)
-		goto out_release_both;
-
-	fd1 = get_unused_fd_flags(flags);
-	if (unlikely(fd1 < 0)) {
-		err = fd1;
-		goto out_release_both;
+	if (unlikely(err < 0)) {
+		sock_release(sock1);
+		goto out;
 	}
 
-	fd2 = get_unused_fd_flags(flags);
-	if (unlikely(fd2 < 0)) {
-		err = fd2;
-		goto out_put_unused_1;
+	err = sock1->ops->socketpair(sock1, sock2);
+	if (unlikely(err < 0)) {
+		sock_release(sock2);
+		sock_release(sock1);
+		goto out;
 	}
 
 	newfile1 = sock_alloc_file(sock1, flags, NULL);
 	if (IS_ERR(newfile1)) {
 		err = PTR_ERR(newfile1);
-		goto out_put_unused_both;
+		sock_release(sock1);
+		sock_release(sock2);
+		goto out;
 	}
 
 	newfile2 = sock_alloc_file(sock2, flags, NULL);
 	if (IS_ERR(newfile2)) {
 		err = PTR_ERR(newfile2);
-		goto out_fput_1;
+		sock_release(sock2);
+		fput(newfile1);
+		goto out;
 	}
 
-	err = put_user(fd1, &usockvec[0]);
-	if (err)
-		goto out_fput_both;
-
-	err = put_user(fd2, &usockvec[1]);
-	if (err)
-		goto out_fput_both;
-
 	audit_fd_pair(fd1, fd2);
 
 	fd_install(fd1, newfile1);
 	fd_install(fd2, newfile2);
-	/* fd1 and fd2 may be already another descriptors.
-	 * Not kernel problem.
-	 */
-
 	return 0;
 
-out_fput_both:
-	fput(newfile2);
-	fput(newfile1);
-	put_unused_fd(fd2);
-	put_unused_fd(fd1);
-	goto out;
-
-out_fput_1:
-	fput(newfile1);
-	put_unused_fd(fd2);
-	put_unused_fd(fd1);
-	sock_release(sock2);
-	goto out;
-
-out_put_unused_both:
+out:
 	put_unused_fd(fd2);
-out_put_unused_1:
 	put_unused_fd(fd1);
-out_release_both:
-	sock_release(sock2);
-out_release_1:
-	sock_release(sock1);
-out:
 	return err;
 }