[PATCH] Check fops_get() return value

From: Laurent Pinchart
Date: Thu Oct 16 2008 - 09:02:47 EST


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@xxxxxxxxxxxxxx>
Signed-off-by: Laurent Pinchart <laurent.pinchart@xxxxxxxxx>
---
drivers/gpu/drm/drm_fops.c | 4 ++++
drivers/media/dvb/dvb-core/dvbdev.c | 5 +++++
sound/core/sound.c | 4 ++++
3 files changed, 13 insertions(+), 0 deletions(-)

diff --git a/drivers/gpu/drm/drm_fops.c b/drivers/gpu/drm/drm_fops.c
index 851a53f..ef5c295 100644
--- a/drivers/gpu/drm/drm_fops.c
+++ b/drivers/gpu/drm/drm_fops.c
@@ -186,6 +186,10 @@ 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);
diff --git a/drivers/media/dvb/dvb-core/dvbdev.c b/drivers/media/dvb/dvb-core/dvbdev.c
index e713277..fb4e241 100644
--- a/drivers/media/dvb/dvb-core/dvbdev.c
+++ b/drivers/media/dvb/dvb-core/dvbdev.c
@@ -85,6 +85,10 @@ 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) {
@@ -95,6 +99,7 @@ static int dvb_device_open(struct inode *inode, struct file *file)
unlock_kernel();
return err;
}
+fail:
unlock_kernel();
return -ENODEV;
}
diff --git a/sound/core/sound.c b/sound/core/sound.c
index c0685e2..8659b84 100644
--- a/sound/core/sound.c
+++ b/sound/core/sound.c
@@ -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) {
--
1.5.0

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