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Check fops_get() return value
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>
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@ -183,6 +183,10 @@ int drm_stub_open(struct inode *inode, struct file *filp)
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old_fops = filp->f_op;
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filp->f_op = fops_get(&dev->driver->fops);
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if (filp->f_op == NULL) {
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filp->f_op = old_fops;
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goto out;
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}
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if (filp->f_op->open && (err = filp->f_op->open(inode, filp))) {
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fops_put(filp->f_op);
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filp->f_op = fops_get(old_fops);
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@ -79,6 +79,10 @@ static int dvb_device_open(struct inode *inode, struct file *file)
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file->private_data = dvbdev;
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old_fops = file->f_op;
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file->f_op = fops_get(dvbdev->fops);
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if (file->f_op == NULL) {
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file->f_op = old_fops;
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goto fail;
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}
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if(file->f_op->open)
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err = file->f_op->open(inode,file);
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if (err) {
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@ -90,6 +94,7 @@ static int dvb_device_open(struct inode *inode, struct file *file)
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unlock_kernel();
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return err;
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}
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fail:
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up_read(&minor_rwsem);
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unlock_kernel();
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return -ENODEV;
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@ -152,6 +152,10 @@ static int __snd_open(struct inode *inode, struct file *file)
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}
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old_fops = file->f_op;
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file->f_op = fops_get(mptr->f_ops);
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if (file->f_op == NULL) {
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file->f_op = old_fops;
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return -ENODEV;
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}
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if (file->f_op->open)
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err = file->f_op->open(inode, file);
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if (err) {
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