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    SubjectRe: [PATCH] media: em28xx: fix corrupted list
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    On 21/07/2021 14:21, Pavel Skripkin wrote:
    > On Tue, 20 Jul 2021 14:13:13 +0200
    > Hans Verkuil <hverkuil@xs4all.nl> wrote:
    >
    >> On 06/07/2021 16:50, Pavel Skripkin wrote:
    >>> Syzbot reported corrupted list in em28xx driver. The problem was in
    >>> non-reinitialized lists on disconnect. Since all 2 lists are global
    >>> variables and driver can be connected and disconnected many times we
    >>> should call INIT_LIST_HEAD() in .disconnect method to prevent
    >>> corrupted list entries.
    >>>
    >>> Fixes: 1a23f81b7dc3 ("V4L/DVB (9979): em28xx: move usb probe code
    >>> to a proper place") Reported-by:
    >>> syzbot+a6969ef522a36d3344c9@syzkaller.appspotmail.com
    >>> Signed-off-by: Pavel Skripkin <paskripkin@gmail.com> ---
    >>> drivers/media/usb/em28xx/em28xx-cards.c | 2 ++
    >>> drivers/media/usb/em28xx/em28xx-core.c | 6 ++++++
    >>> drivers/media/usb/em28xx/em28xx.h | 1 +
    >>> 3 files changed, 9 insertions(+)
    >>>
    >>> diff --git a/drivers/media/usb/em28xx/em28xx-cards.c
    >>> b/drivers/media/usb/em28xx/em28xx-cards.c index
    >>> ba9292e2a587..8b1ff79c37a0 100644 ---
    >>> a/drivers/media/usb/em28xx/em28xx-cards.c +++
    >>> b/drivers/media/usb/em28xx/em28xx-cards.c @@ -4148,6 +4148,8 @@
    >>> static void em28xx_usb_disconnect(struct usb_interface *intf)
    >>> dev->dev_next = NULL; }
    >>> kref_put(&dev->ref, em28xx_free_device);
    >>> +
    >>> + em28xx_reset_lists();
    >>> }
    >>>
    >>> static int em28xx_usb_suspend(struct usb_interface *intf,
    >>> diff --git a/drivers/media/usb/em28xx/em28xx-core.c
    >>> b/drivers/media/usb/em28xx/em28xx-core.c index
    >>> 584fa400cd7d..03970ed00dba 100644 ---
    >>> a/drivers/media/usb/em28xx/em28xx-core.c +++
    >>> b/drivers/media/usb/em28xx/em28xx-core.c @@ -1131,6 +1131,12 @@
    >>> void em28xx_init_extension(struct em28xx *dev)
    >>> mutex_unlock(&em28xx_devlist_mutex); }
    >>>
    >>> +void em28xx_reset_lists(void)
    >>> +{
    >>> + INIT_LIST_HEAD(&em28xx_devlist);
    >>> + INIT_LIST_HEAD(&em28xx_extension_devlist);
    >>
    >> This needs a mutex_lock(&em28xx_devlist_mutex);
    >>
    >> But actually, I don't think this is right: if there are multiple
    >> em28xx devices, then I think if you disconnect one, then the other is
    >> - with this code - also removed from the list.
    >>
    >> Can you give a link to the actual syzbot bug? I'm not at all sure you
    >> are fixing the right thing here.
    >
    > Hi, Hans!
    >
    > I guess, I missed my coffee that morning, sorry :) This patch looks
    > complety wrong, of course.
    >
    > I've took a close look at this bug one more time, and I found the true
    > root case of this bug.
    >
    > If em28xx dev has dev_next pointer we need to close dev->next extension
    > on disconnect to avoid UAF and corrupted list bug. So, something like
    > this should work:
    >
    > diff --git a/drivers/media/usb/em28xx/em28xx-cards.c b/drivers/media/usb/em28xx/em28xx-cards.c
    > index c1e0dccb7408..d56b040e1bd7 100644
    > --- a/drivers/media/usb/em28xx/em28xx-cards.c
    > +++ b/drivers/media/usb/em28xx/em28xx-cards.c
    > @@ -4139,8 +4139,10 @@ static void em28xx_usb_disconnect(struct usb_interface *intf)
    >
    > em28xx_close_extension(dev);
    >
    > - if (dev->dev_next)
    > + if (dev->dev_next) {
    > em28xx_release_resources(dev->dev_next);
    > + em28xx_close_extension(dev->dev_next);
    > + }
    > em28xx_release_resources(dev);
    >
    > if (dev->dev_next) {
    >
    > How to You feel about it? I am going to send this patch for syzbot
    > testing

    That looks a lot saner :-)

    >
    >
    > Syzbot link:
    > https://syzkaller.appspot.com/bug?id=3609bbf45bf63a8f6032f330eb3d34f51cc81493
    >
    >
    > Again, sorry for v1 patch, I don't know how I came up with this fix :(

    No problem, just post a v2 if syzbot passes.

    Regards,

    Hans

    >
    >
    >
    > With regards,
    > Pavel Skripkin
    >

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