On Thu, Jan 16 2014, Andrzej Pietrasiewicz wrote:
> Fix possible NULL pointer dereference introduced in
>
> 219580e64f035bb9018dbb08d340f90b0ac50f8c
> usb: f_fs: check quirk to pad epout buf size when not aligned to
> maxpacketsize
>
> after 3.13-rc1.
>
> In cases we do wait with:
>
> wait_event_interruptible(epfile->wait, (ep = epfile->ep));
>
> for endpoint to be enabled, functionfs_bind() has not been called yet
> and epfile->ffs->gadget is still NULL and the automatic variable 'gadget'
> has been initialized with NULL at the point of its definition.
> Later on it is used as a parameter to:
>
> usb_ep_align_maybe(gadget, ep->ep, len)
>
> which in turn dereferences it.
>
> This patch fixes it by moving the actual assignment to the local 'gadget'
> variable after the potential waiting has completed.
>
> Signed-off-by: Andrzej Pietrasiewicz <andrzej.p@xxxxxxxxxxx>
Acked-by: Michal Nazarewicz <mina86@xxxxxxxxxx>
But since gadget is only used in the “if (!halt)” part of the code,
could you simply move definition of the variable inside the if?
> ---
> drivers/usb/gadget/f_fs.c | 7 ++++++-
> 1 files changed, 6 insertions(+), 1 deletions(-)
>
> diff --git a/drivers/usb/gadget/f_fs.c b/drivers/usb/gadget/f_fs.c
> index fffda61..e84b73b 100644
> --- a/drivers/usb/gadget/f_fs.c
> +++ b/drivers/usb/gadget/f_fs.c
> @@ -587,7 +587,7 @@ static ssize_t ffs_epfile_io(struct file *file,
> char __user *buf, size_t len, int read)
> {
> struct ffs_epfile *epfile = file->private_data;
> - struct usb_gadget *gadget = epfile->ffs->gadget;
> + struct usb_gadget *gadget;
> struct ffs_ep *ep;
> char *data = NULL;
> ssize_t ret, data_len;
> @@ -613,6 +613,11 @@ static ssize_t ffs_epfile_io(struct file *file,
> goto error;
> }
> }
> + /*
> + * if we _do_ wait above, the epfile->ffs->gadget might be NULL
> + * before the waiting completes, so do not assign to 'gadget' earlier
> + */
> + gadget = epfile->ffs->gadget;
>
> /* Do we halt? */
> halt = !read == !epfile->in;
--
Best regards, _ _
.o. | Liege of Serenely Enlightened Majesty of o' \,=./ `o
..o | Computer Science, Michał “mina86” Nazarewicz (o o)
ooo +--<mpn@xxxxxxxxxx>--<xmpp:mina86@xxxxxxxxxx>--ooO--(_)--Ooo--
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