linux-kernel - Re: [PATCH] Userfaultfd: Avoid double free of userfault_ctx and remove O

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Date:   Tue, 4 Aug 2020 13:45:43 -0700
From:   Eric Biggers <ebiggers@...nel.org>
To:     Lokesh Gidra <lokeshgidra@...gle.com>
Cc:     viro@...iv.linux.org.uk, stephen.smalley.work@...il.com,
        casey@...aufler-ca.com, jmorris@...ei.org, kaleshsingh@...gle.com,
        dancol@...col.org, surenb@...gle.com,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        nnk@...gle.com, jeffv@...gle.com, calin@...gle.com,
        kernel-team@...roid.com, yanfei.xu@...driver.com,
        syzbot+75867c44841cb6373570@...kaller.appspotmail.com
Subject: Re: [PATCH] Userfaultfd: Avoid double free of userfault_ctx and
 remove O_CLOEXEC

On Tue, Aug 04, 2020 at 01:31:55PM -0700, Lokesh Gidra wrote:
> when get_unused_fd_flags returns error, ctx will be freed by
> userfaultfd's release function, which is indirectly called by fput().
> Also, if anon_inode_getfile_secure() returns an error, then
> userfaultfd_ctx_put() is called, which calls mmdrop() and frees ctx.
> 
> Also, the O_CLOEXEC was inadvertently added to the call to
> get_unused_fd_flags() [1].
> 
> Adding Al Viro's suggested-by, based on [2].
> 
> [1] https://lore.kernel.org/lkml/1f69c0ab-5791-974f-8bc0-3997ab1d61ea@dancol.org/
> [2] https://lore.kernel.org/lkml/20200719165746.GJ2786714@ZenIV.linux.org.uk/
> 
> Fixes: d08ac70b1e0d (Wire UFFD up to SELinux)
> Suggested-by: Al Viro <viro@...iv.linux.org.uk>
> Reported-by: syzbot+75867c44841cb6373570@...kaller.appspotmail.com
> Signed-off-by: Lokesh Gidra <lokeshgidra@...gle.com>

What branch does this patch apply to?  Neither mainline nor linux-next works.

- Eric