Commit e3a2a0d4 authored Dec 02, 2008 by Christian Borntraeger Committed by Avi Kivity Dec 31, 2008

anon_inodes: use fops->owner for module refcount



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. The refcounting was
tested with a patched and unpatched KVM module.(see patch 2/2) I also did an
epoll_open/close test.

Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Reviewed-by: Davide Libenzi <davidel@xmailserver.org>
Signed-off-by: Avi Kivity <avi@redhat.com>

parent e93353c9

fs/anon_inodes.c

+6 −1

Original line number	Diff line number	Diff line
		@@ -79,9 +79,12 @@ int anon_inode_getfd(const char name, const struct file_operations fops,
		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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