From 1ff13c78ca3975a94460a6a0b49acf9a787ed350 Mon Sep 17 00:00:00 2001 From: Ian Abbott Date: Wed, 27 Feb 2013 10:56:19 +0000 Subject: [PATCH] staging: comedi: check s->async for poll(), read() and write() commit cc400e185c07c15a42d2635995f422de5b94b696 upstream. 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 Signed-off-by: Ben Hutchings --- drivers/staging/comedi/comedi_fops.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/drivers/staging/comedi/comedi_fops.c b/drivers/staging/comedi/comedi_fops.c index 13e79a1110fa..a023f522408d 100644 --- a/drivers/staging/comedi/comedi_fops.c +++ b/drivers/staging/comedi/comedi_fops.c @@ -1574,7 +1574,7 @@ static unsigned int comedi_poll(struct file *file, poll_table * wait) mask = 0; read_subdev = comedi_get_read_subdevice(dev_file_info); - if (read_subdev) { + if (read_subdev && read_subdev->async) { poll_wait(file, &read_subdev->async->wait_head, wait); if (!read_subdev->busy || comedi_buf_read_n_available(read_subdev->async) > 0 @@ -1584,7 +1584,7 @@ static unsigned int comedi_poll(struct file *file, poll_table * wait) } } write_subdev = comedi_get_write_subdevice(dev_file_info); - if (write_subdev) { + if (write_subdev && write_subdev->async) { poll_wait(file, &write_subdev->async->wait_head, wait); comedi_buf_write_alloc(write_subdev->async, write_subdev->async->prealloc_bufsz); @@ -1626,7 +1626,7 @@ static ssize_t comedi_write(struct file *file, const char __user *buf, } s = comedi_get_write_subdevice(dev_file_info); - if (s == NULL) { + if (s == NULL || s->async == NULL) { retval = -EIO; goto done; } @@ -1737,7 +1737,7 @@ static ssize_t comedi_read(struct file *file, char __user *buf, size_t nbytes, } s = comedi_get_read_subdevice(dev_file_info); - if (s == NULL) { + if (s == NULL || s->async == NULL) { retval = -EIO; goto done; } -- 2.30.2