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>

1 files changed, 9 insertions, 3 deletions

diff --git a/drivers/media/dvb/dvb-core/dmxdev.c b/drivers/media/dvb/dvb-core/dmxdev.c
index 09e96e9ddbdf..04578df3f249 100644
--- 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
 };