> > + if (fops->owner && !try_module_get(fops->owner))
> > + return -ENOENT;
> > +
> > error = get_unused_fd_flags(flags);
> > if (error < 0)
> > return error;
>
> What if get_unused_fd_flags() (or the following error-returing ops) fails
> after a successful try_module_get()?
Right, well spotted. I have added a fixup label.
From: Christian Borntraeger <borntraeger@xxxxxxxxxx>
There is an imbalance for anonymous inodes. If the fops->owner field is set,
the module reference count of owner is decreases on release.
("filp_close" --> "__fput" ---> "fops_put")
On the other hand, anon_inode_getfd does not increase the module reference
count of owner. This causes two problems:
- if owner is set, the module refcount goes negative
- if owner is not set, the module can be unloaded while code is running
This patch changes anon_inode_getfd to be symmetric regarding fops->owner
handling.
I have checked all existing users of anon_inode_getfd. Noone sets fops->owner,
thats why nobody has seen the module refcount negative.
Signed-off-by: Christian Borntraeger <borntraeger@xxxxxxxxxx>
From: Christian Borntraeger <borntraeger@xxxxxxxxxx>
There is an imbalance for anonymous inodes. If the fops->owner field is set,
the module reference count of owner is decreases on release.
("filp_close" --> "__fput" ---> "fops_put")
On the other hand, anon_inode_getfd does not increase the module reference
count of owner. This causes two problems:
- if owner is set, the module refcount goes negative
- if owner is not set, the module can be unloaded while code is running
This patch changes anon_inode_getfd to be symmetric regarding fops->owner
handling.
I have checked all existing users of anon_inode_getfd. Noone sets fops->owner,
thats why nobody has seen the module refcount negative.
Signed-off-by: Christian Borntraeger <borntraeger@xxxxxxxxxx>
---
fs/anon_inodes.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)
Index: kvm/fs/anon_inodes.c
===================================================================
--- kvm.orig/fs/anon_inodes.c
+++ kvm/fs/anon_inodes.c
@@ -79,9 +79,12 @@ int anon_inode_getfd(const char *name, c
if (IS_ERR(anon_inode_inode))
return -ENODEV;
+ if (fops->owner && !try_module_get(fops->owner))
+ return -ENOENT;
+
error = get_unused_fd_flags(flags);
if (error < 0)
- return error;
+ goto err_module;
fd = error;
/*
@@ -128,6 +131,8 @@ err_dput:
dput(dentry);
err_put_unused_fd:
put_unused_fd(fd);
+err_module:
+ module_put(fops->owner);
return error;
}
EXPORT_SYMBOL_GPL(anon_inode_getfd);
--
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