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staging: comedi: check s->async for poll(), read() and write() 

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>
This commit is contained in:
Ian Abbott 2013-02-05 12:50:40 +00:00 committed by Greg Kroah-Hartman
parent 4a79f73017
commit cc400e185c
1 changed files with 4 additions and 4 deletions
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8
drivers/staging/comedi/comedi_fops.c
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@ -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;