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Check fops_get() return value

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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>
This commit is contained in:
Laurent Pinchart 2009-01-06 14:40:40 -08:00 committed by Linus Torvalds
parent bdbeed75b2
commit f41ced8f10
3 changed files with 13 additions and 0 deletions
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4
drivers/gpu/drm/drm_fops.c
View 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);

5
drivers/media/dvb/dvb-core/dvbdev.c
View 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;

4
sound/core/sound.c
View 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) {