From: Peilin Ye <yepeilin.cs@gmail.com>
To: Daniel Colascione <dancol@google.com>
Cc: timmurray@google.com, selinux@vger.kernel.org,
linux-security-module@vger.kernel.org,
linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
kvm@vger.kernel.org, viro@zeniv.linux.org.uk,
paul@paul-moore.com, nnk@google.com, sds@tycho.nsa.gov,
lokeshgidra@google.com, jmorris@namei.org
Subject: Reporting a use-after-free read bug in userfaultfd_release()
Date: Fri, 17 Jul 2020 07:45:32 -0400 [thread overview]
Message-ID: <20200717114532.GA688728@PWN> (raw)
Hi all,
Syzbot reported the following use-after-free bug in
userfaultfd_release():
https://syzkaller.appspot.com/bug?id=4b9e5aea757b678d9939c364e50212354a3480a6
It seems to be caused by this patch. I took a look at the stack trace.
In the patch:
fd = get_unused_fd_flags(O_RDONLY | O_CLOEXEC);
if (fd < 0) {
fput(file);
goto out;
}
If get_unused_fd_flags() fails, `ctx` is freed. Later however, before
returning back to userland, userfaultfd_release() is called and tries to
use `ctx` again, causing a use-after-free bug.
The syzbot reproducer does a setrlimit() then a userfaultfd(). The
former sets a hard limit on number of open files to zero, which causes
get_unused_fd_flags() to fail.
Thank you,
Peilin Ye
reply other threads:[~2020-07-17 11:45 UTC|newest]
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