Messages in this thread Patch in this message | | | From | Laurent Pinchart <> | Subject | [PATCH] Check fops_get() return value | Date | Thu, 16 Oct 2008 15:02:40 +0200 |
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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> --- 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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