V4L/DVB (3672): Fix memory leak in dvr open

The dvr device could be opened multiple times simultaneously in O_RDONLY mode.
Each open after the first would allocate a new dvr buffer (1880 KB) and leak
the old buffer.  The first close would de-allocate the dvr buffer and cause
all other open dvrs to stop working.  This patch allows only a single O_RDONLY
open of the drv device, as per the API specification.  Multiple O_WRONLY opens
are still allowed and don't appear to cause any problems.

Signed-off-by: Trent Piepho <xyzzy@speakeasy.org>
Signed-off-by: Andrew de Quincey <adq_dvb@lidskialf.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>

diff --git a/drivers/media/dvb/dvb-core/dmxdev.c b/drivers/media/dvb/dvb-core/dmxdev.c
index 09e96e9..04578df 100644 (file)
--- a/drivers/media/dvb/dvb-core/dmxdev.c
+++ b/drivers/media/dvb/dvb-core/dmxdev.c
@@ -141,12 +141,18 @@ static int dvb_dvr_open(struct inode *inode, struct file *file)
        }
 
        if ((file->f_flags & O_ACCMODE) == O_RDONLY) {
-               void *mem = vmalloc(DVR_BUFFER_SIZE);
+               void *mem;
+               if (!dvbdev->readers) {
+                       mutex_unlock(&dmxdev->mutex);
+                       return -EBUSY;
+               }
+               mem = vmalloc(DVR_BUFFER_SIZE);
                if (!mem) {
                        mutex_unlock(&dmxdev->mutex);
                        return -ENOMEM;
                }
                dvb_ringbuffer_init(&dmxdev->dvr_buffer, mem, DVR_BUFFER_SIZE);
+               dvbdev->readers--;
        }
 
        if ((file->f_flags & O_ACCMODE) == O_WRONLY) {
@@ -184,6 +190,7 @@ static int dvb_dvr_release(struct inode *inode, struct file *file)
                                                dmxdev->dvr_orig_fe);
        }
        if ((file->f_flags & O_ACCMODE) == O_RDONLY) {
+               dvbdev->readers++;
                if (dmxdev->dvr_buffer.data) {
                        void *mem = dmxdev->dvr_buffer.data;
                        mb();
@@ -1029,8 +1036,7 @@ static struct file_operations dvb_dvr_fops = {
 
 static struct dvb_device dvbdev_dvr = {
        .priv = NULL,
-       .users = 1,
-       .writers = 1,
+       .readers = 1,
        .fops = &dvb_dvr_fops
 };