Check fops_get() return value
Laurent Pinchart [Tue, 6 Jan 2009 22:40:40 +0000 (14:40 -0800)]
Several subsystem open handlers dereference the fops_get() return value
without checking it for nullness.  This opens a race condition between the
open handler and module unloading.

A module can be marked as being unloaded (MODULE_STATE_GOING) before its
exit function is called and gets the chance to unregister the driver.
During that window open handlers can still be called, and fops_get() will
fail in try_module_get() and return a NULL pointer.

This change checks the fops_get() return value and returns -ENODEV if NULL.

Reported-by: Alan Jenkins <alan-jenkins@tuffmail.co.uk>
Signed-off-by: Laurent Pinchart <laurent.pinchart@skynet.be>
Acked-by: Takashi Iwai <tiwai@suse.de>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Dave Airlie <airlied@linux.ie>
Acked-by: Mauro Carvalho Chehab <mchehab@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/gpu/drm/drm_fops.c
drivers/media/dvb/dvb-core/dvbdev.c
sound/core/sound.c

index 3733e36..b06a537 100644 (file)
@@ -183,6 +183,10 @@ int drm_stub_open(struct inode *inode, struct file *filp)
 
        old_fops = filp->f_op;
        filp->f_op = fops_get(&dev->driver->fops);
+       if (filp->f_op == NULL) {
+               filp->f_op = old_fops;
+               goto out;
+       }
        if (filp->f_op->open && (err = filp->f_op->open(inode, filp))) {
                fops_put(filp->f_op);
                filp->f_op = fops_get(old_fops);
index 65d6966..6a32680 100644 (file)
@@ -79,6 +79,10 @@ static int dvb_device_open(struct inode *inode, struct file *file)
                file->private_data = dvbdev;
                old_fops = file->f_op;
                file->f_op = fops_get(dvbdev->fops);
+               if (file->f_op == NULL) {
+                       file->f_op = old_fops;
+                       goto fail;
+               }
                if(file->f_op->open)
                        err = file->f_op->open(inode,file);
                if (err) {
@@ -90,6 +94,7 @@ static int dvb_device_open(struct inode *inode, struct file *file)
                unlock_kernel();
                return err;
        }
+fail:
        up_read(&minor_rwsem);
        unlock_kernel();
        return -ENODEV;
index 44a69bb..7872a02 100644 (file)
@@ -152,6 +152,10 @@ static int __snd_open(struct inode *inode, struct file *file)
        }
        old_fops = file->f_op;
        file->f_op = fops_get(mptr->f_ops);
+       if (file->f_op == NULL) {
+               file->f_op = old_fops;
+               return -ENODEV;
+       }
        if (file->f_op->open)
                err = file->f_op->open(inode, file);
        if (err) {