staging: comedi: check s->async for poll(), read() and write() (cc400e18) · Commits · 戴 / test

Some low-level comedi drivers (incorrectly) point `dev->read_subdev` or `dev->write_subdev` to a subdevice that does not support asynchronous commands. Comedi's poll(), read() and write() file operation handlers assume these subdevices do support asynchronous commands. In particular, they assume `s->async` is valid (where `s` points to the read or write subdevice), which it won't be if it has been set incorrectly. This can lead to a NULL pointer dereference. Check `s->async` is non-NULL in `comedi_poll()`, `comedi_read()` and `comedi_write()` to avoid the bug. Signed-off-by:

Ian Abbott <abbotti@mev.co.uk> Cc: stable <stable@vger.kernel.org> Signed-off-by:

Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/comedi/comedi_fops.c

+4 −4

Original line number	Diff line number	Diff line
		@@ -1839,7 +1839,7 @@ static unsigned int comedi_poll(struct file file, poll_table wait)
		}

		s = comedi_read_subdevice(info);
		if (s) {
		if (s && s->async) {
		poll_wait(file, &s->async->wait_head, wait);
		if (!s->busy \|\| !comedi_is_subdevice_running(s) \|\|
		comedi_buf_read_n_available(s->async) > 0)
		@@ -1847,7 +1847,7 @@ static unsigned int comedi_poll(struct file file, poll_table wait)
		}

		s = comedi_write_subdevice(info);
		if (s) {
		if (s && s->async) {
		unsigned int bps = bytes_per_sample(s->async->subdevice);

		poll_wait(file, &s->async->wait_head, wait);
		@@ -1882,7 +1882,7 @@ static ssize_t comedi_write(struct file file, const char __user buf,
		}

		s = comedi_write_subdevice(info);
		if (!s)
		if (!s \|\| !s->async)
		return -EIO;

		async = s->async;
		@@ -1977,7 +1977,7 @@ static ssize_t comedi_read(struct file file, char __user buf, size_t nbytes,
		}

		s = comedi_read_subdevice(info);
		if (!s)
		if (!s \|\| !s->async)
		return -EIO;

		async = s->async;

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