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>
diff --git a/drivers/gpu/drm/drm_fops.c b/drivers/gpu/drm/drm_fops.c
index 3733e36..b06a537 100644
--- a/drivers/gpu/drm/drm_fops.c
+++ b/drivers/gpu/drm/drm_fops.c
@@ -183,6 +183,10 @@
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);