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Subject[patch 54/88] anon_inodes: use fops->owner for module refcount

2.6.28-stable review patch. If anyone has any objections, please let us know.

------------------

From: Christian Borntraeger <borntraeger@de.ibm.com>

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>
(cherry picked from commit e3a2a0d4e5ace731e60e2eff4fb7056ecb34adc1)
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
---
fs/anon_inodes.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)

--- a/fs/anon_inodes.c
+++ b/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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