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From:   Eric Biggers <ebiggers@kernel.org>
To:     David Howells <dhowells@redhat.com>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        linux-fsdevel@vger.kernel.org
Cc:     Mark Rutland <mark.rutland@arm.com>, linux-kernel@vger.kernel.org
Subject: [PATCH] vfs: fsmount: add missing mntget()
Date:   Wed, 12 Jun 2019 11:43:13 -0700
Message-Id: <20190612184313.143456-1-ebiggers@kernel.org>
In-Reply-To: <20190610183031.GE63833@gmail.com>
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From: Eric Biggers <ebiggers@google.com>

sys_fsmount() needs to take a reference to the new mount when adding it
to the anonymous mount namespace.  Otherwise the filesystem can be
unmounted while it's still in use, as found by syzkaller.

Reported-by: Mark Rutland <mark.rutland@arm.com>
Reported-by: syzbot+99de05d099a170867f22@syzkaller.appspotmail.com
Reported-by: syzbot+7008b8b8ba7df475fdc8@syzkaller.appspotmail.com
Fixes: 93766fbd2696 ("vfs: syscall: Add fsmount() to create a mount for a superblock")
Signed-off-by: Eric Biggers <ebiggers@google.com>
---
 fs/namespace.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/fs/namespace.c b/fs/namespace.c
index b26778bdc236e..5dc137a22d406 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -3445,6 +3445,7 @@ SYSCALL_DEFINE3(fsmount, int, fs_fd, unsigned int, flags,
 	ns->root = mnt;
 	ns->mounts = 1;
 	list_add(&mnt->mnt_list, &ns->list);
+	mntget(newmount.mnt);
 
 	/* Attach to an apparent O_PATH fd with a note that we need to unmount
 	 * it, not just simply put it.
-- 
2.22.0.rc2.383.gf4fbbf30c2-goog