From 67913bbd0b62d297520667cd3057aff5a5890ca6 Mon Sep 17 00:00:00 2001 From: Michal Nazarewicz Date: Wed, 10 Sep 2014 17:50:24 +0200 Subject: [PATCH] usb: gadget: f_fs: refactor and document __ffs_ep0_read_events better Instead of using variable length array, use a static length equal to the size of the ffs->ev.types array. This gets rid of a sparse warning: drivers/usb/gadget/function/f_fs.c:401:44: warning: Variable length array is used. and makes it more explicit that the array has a very tight upper size limit. Also add some more documentation about the ev.types array and how its size is limited and affects the rest of the code. Reported-by: Dan Carpenter Reported-by: Rohith Seelaboyina Signed-off-by: Michal Nazarewicz Signed-off-by: Felipe Balbi --- drivers/usb/gadget/function/f_fs.c | 28 +++++++++++++++++----------- 1 file changed, 17 insertions(+), 11 deletions(-) diff --git a/drivers/usb/gadget/function/f_fs.c b/drivers/usb/gadget/function/f_fs.c index 63314ede7ba6..a00ee977305c 100644 --- a/drivers/usb/gadget/function/f_fs.c +++ b/drivers/usb/gadget/function/f_fs.c @@ -390,17 +390,20 @@ done_spin: return ret; } +/* Called with ffs->ev.waitq.lock and ffs->mutex held, both released on exit. */ static ssize_t __ffs_ep0_read_events(struct ffs_data *ffs, char __user *buf, size_t n) { /* - * We are holding ffs->ev.waitq.lock and ffs->mutex and we need - * to release them. + * n cannot be bigger than ffs->ev.count, which cannot be bigger than + * size of ffs->ev.types array (which is four) so that's how much space + * we reserve. */ - struct usb_functionfs_event events[n]; + struct usb_functionfs_event events[ARRAY_SIZE(ffs->ev.types)]; + const size_t size = n * sizeof *events; unsigned i = 0; - memset(events, 0, sizeof events); + memset(events, 0, size); do { events[i].type = ffs->ev.types[i]; @@ -410,19 +413,15 @@ static ssize_t __ffs_ep0_read_events(struct ffs_data *ffs, char __user *buf, } } while (++i < n); - if (n < ffs->ev.count) { - ffs->ev.count -= n; + ffs->ev.count -= n; + if (ffs->ev.count) memmove(ffs->ev.types, ffs->ev.types + n, ffs->ev.count * sizeof *ffs->ev.types); - } else { - ffs->ev.count = 0; - } spin_unlock_irq(&ffs->ev.waitq.lock); mutex_unlock(&ffs->mutex); - return unlikely(__copy_to_user(buf, events, sizeof events)) - ? -EFAULT : sizeof events; + return unlikely(__copy_to_user(buf, events, size)) ? -EFAULT : size; } static ssize_t ffs_ep0_read(struct file *file, char __user *buf, @@ -2377,6 +2376,13 @@ static void __ffs_event_add(struct ffs_data *ffs, if (ffs->setup_state == FFS_SETUP_PENDING) ffs->setup_state = FFS_SETUP_CANCELLED; + /* + * Logic of this function guarantees that there are at most four pending + * evens on ffs->ev.types queue. This is important because the queue + * has space for four elements only and __ffs_ep0_read_events function + * depends on that limit as well. If more event types are added, those + * limits have to be revisited or guaranteed to still hold. + */ switch (type) { case FUNCTIONFS_RESUME: rem_type2 = FUNCTIONFS_SUSPEND; -- 2.30.2