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SubjectRe: [PATCH] fsi:fsi-sbefifo: Fix possible concurrency use-after-free bugs in sbefifo_user_release
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On Wed, 2018-12-26 at 21:56 +0800, Jia-Ju Bai wrote:
> In drivers/fsi/fsi-sbefifo.c, the functions sbefifo_user_release(),
> sbefifo_user_read() and sbefifo_user_write() may be concurrently executed.

So after refreshing my mind, looking at the code and talking with Al, I
really dont' see what race you are trying to fix here.

read/write should never be concurrent with release for a given file and
the stuff we are protecting here is local to the file instance.

Do you have an actual problem you observed ?

Cheers,
Ben.

> sbefifo_user_release()
> sbefifo_release_command()
> vfree(user->pending_cmd);
>
> sbefifo_user_read()
> mutex_lock();
> rc = __sbefifo_submit(sbefifo, user->pending_cmd, ...);
>
> sbefifo_user_write()
> mutex_lock();
> user->pending_cmd = user->cmd_page;
> user->pending_cmd = vmalloc(len);
>
> Thus, possible concurrency use-after-free bugs may occur in
> sbefifo_user_release().
>
> To fix these bugs, the calls to mutex_lock() and mutex_unlock() are
> added in sbefifo_user_release().
>
>
> Signed-off-by: Jia-Ju Bai <baijiaju1990@gmail.com>
> ---
> drivers/fsi/fsi-sbefifo.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/drivers/fsi/fsi-sbefifo.c b/drivers/fsi/fsi-sbefifo.c
> index d92f5b87c251..e278a9014b8f 100644
> --- a/drivers/fsi/fsi-sbefifo.c
> +++ b/drivers/fsi/fsi-sbefifo.c
> @@ -900,8 +900,10 @@ static int sbefifo_user_release(struct inode *inode, struct file *file)
> if (!user)
> return -EINVAL;
>
> + mutex_lock(&user->file_lock);
> sbefifo_release_command(user);
> free_page((unsigned long)user->cmd_page);
> + mutex_unlock(&user->file_lock);
> kfree(user);
>
> return 0;

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