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    SubjectRe: [PATCH v3 10/12] ima: defer calling __fput()
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    Hello,


    On Wed, Mar 21, 2012 at 8:54 PM, Mimi Zohar <zohar@linux.vnet.ibm.com> wrote:
    > If a file is closed before it is munmapped, __fput() is called with
    > the mmap_sem taken.  With IMA-appraisal enabled, this results in an
    > mmap_sem/i_mutex lockdep.  ima_defer_fput() increments the f_count
    > to defer __fput() being called until after the mmap_sem is released.
    >

    Have you noticed any performance implications?


    > Changelog v3:
    > - use slab mempool (suggested by Dmitry Kasatkin)
    > - renamed a few functions based on Matt Helsley's review
    > - define ima_fput_mempool as static (fix sparse error)
    > - fix ima_defer_fput() stub definition
    >
    > Changelog v2:
    > - based on discussions with: Tyler Hicks (use workqueues),
    >  Dave Hansen (defer only IMA related files), and
    >  Dmitry Kasatkin (add new IMA hook)
    > - use slab memory for allocating work
    >
    > Signed-off-by: Mimi Zohar <zohar@us.ibm.com>
    > ---
    >  include/linux/ima.h                   |    5 ++
    >  mm/mmap.c                             |    1 +
    >  security/integrity/ima/ima_appraise.c |   84 +++++++++++++++++++++++++++++++++
    >  3 files changed, 90 insertions(+), 0 deletions(-)
    >
    > diff --git a/include/linux/ima.h b/include/linux/ima.h
    > index 2c7223d..af8cb3b 100644
    > --- a/include/linux/ima.h
    > +++ b/include/linux/ima.h
    > @@ -47,6 +47,7 @@ extern void ima_inode_post_setattr(struct dentry *dentry);
    >  extern int ima_inode_setxattr(struct dentry *dentry, const char *xattr_name,
    >                       const void *xattr_value, size_t xattr_value_len);
    >  extern int ima_inode_removexattr(struct dentry *dentry, const char *xattr_name);
    > +extern void ima_defer_fput(struct file *file);
    >  #else
    >  static inline void ima_inode_post_setattr(struct dentry *dentry)
    >  {
    > @@ -66,5 +67,9 @@ static inline int ima_inode_removexattr(struct dentry *dentry,
    >  {
    >        return 0;
    >  }
    > +static inline void ima_defer_fput(struct file *file)
    > +{
    > +       return;
    > +}
    >  #endif /* CONFIG_IMA_APPRAISE_H */
    >  #endif /* _LINUX_IMA_H */
    > diff --git a/mm/mmap.c b/mm/mmap.c
    > index 4c16a0a..c1accd4 100644
    > --- a/mm/mmap.c
    > +++ b/mm/mmap.c
    > @@ -232,6 +232,7 @@ static struct vm_area_struct *remove_vma(struct vm_area_struct *vma)
    >        if (vma->vm_ops && vma->vm_ops->close)
    >                vma->vm_ops->close(vma);
    >        if (vma->vm_file) {
    > +               ima_defer_fput(vma->vm_file); /* drop mmap_sem first */
    >                fput(vma->vm_file);
    >                if (vma->vm_flags & VM_EXECUTABLE)
    >                        removed_exe_file_vma(vma->vm_mm);
    > diff --git a/security/integrity/ima/ima_appraise.c b/security/integrity/ima/ima_appraise.c
    > index becc7e0..a100a3c 100644
    > --- a/security/integrity/ima/ima_appraise.c
    > +++ b/security/integrity/ima/ima_appraise.c
    > @@ -11,6 +11,7 @@
    >  #include <linux/module.h>
    >  #include <linux/file.h>
    >  #include <linux/fs.h>
    > +#include <linux/mempool.h>
    >  #include <linux/xattr.h>
    >  #include <linux/magic.h>
    >  #include <linux/ima.h>
    > @@ -226,3 +227,86 @@ int ima_inode_removexattr(struct dentry *dentry, const char *xattr_name)
    >        }
    >        return result;
    >  }
    > +
    > +struct ima_fput_req {
    > +       struct file *file;
    > +       struct work_struct work;
    > +};
    > +static struct kmem_cache *ima_fput_slab;
    > +static mempool_t *ima_fput_mempool;
    > +
    > +static void ima_deferred_fput(struct work_struct *work)
    > +{
    > +       struct ima_fput_req *deferred = container_of(work, struct ima_fput_req,
    > +                                                    work);
    > +
    > +       fput(deferred->file);
    > +       mempool_free(deferred, ima_fput_mempool);
    > +}
    > +
    > +/**
    > + * ima_defer_fput - defer calling __fput() for mmaped files
    > + * @file: pointer to file structure to be freed
    > + *
    > + * The i_mutex is taken by ima_file_free(), called on  __fput(), to
    > + * update 'security.ima' to reflect the current file data hash.  When
    > + * a file is closed before it is munmapped, __fput() is called with
    > + * the mmap_sem taken, resulting in an mmap_sem/i_mutex lockdep.
    > + * This function defers calling __fput() until after the mmap_sem is
    > + * released.
    > + */
    > +void ima_defer_fput(struct file *file)
    > +{
    > +       struct dentry *dentry = file->f_path.dentry;
    > +       struct inode *inode = dentry->d_inode;
    > +       struct ima_fput_req *defer;
    > +       int rc;
    > +
    > +       if (!IS_IMA(inode))
    > +               return;
    > +
    > +       defer = mempool_alloc(ima_fput_mempool, GFP_NOIO);
    > +       if (!defer)
    > +               return;
    > +
    > +       get_file(file);
    > +
    > +       defer->file = file;
    > +       INIT_WORK(&defer->work, ima_deferred_fput);
    > +       rc = schedule_work(&defer->work);
    > +       if (rc == 0) {
    > +               pr_info("ima: schedule work failed\n");
    > +               mempool_free(defer, ima_fput_mempool);
    > +               fput_atomic(file);
    > +       }
    > +}
    > +
    > +static int __init ima_fput_mempool_create(void)
    > +{
    > +       ima_fput_slab = kmem_cache_create("ima_fput",
    > +                                          sizeof(struct ima_fput_req),
    > +                                          0, 0, NULL);
    > +       if (!ima_fput_slab) {
    > +               pr_info("ima: failed kmem_cache_create\n");
    > +               goto err_out;
    > +       }
    > +
    > +       ima_fput_mempool = mempool_create_slab_pool(1, ima_fput_slab);
    > +       if (!ima_fput_mempool)  {
    > +               pr_info("ima: failed mempool_create_slab_pool\n");
    > +               goto free_slab;
    > +       }
    > +       return 0;
    > +
    > +free_slab:
    > +       kmem_cache_destroy(ima_fput_slab);
    > +err_out:
    > +       return -ENOMEM;
    > +}
    > +
    > +static void __exit ima_fput_mempool_destroy(void)
    > +{
    > +       mempool_destroy(ima_fput_mempool);
    > +       kmem_cache_destroy(ima_fput_slab);
    > +}

    Is it really needed? I think it will never be called if not a module...

    > +security_initcall(ima_fput_mempool_create);
    > --
    > 1.7.6.5
    >
    --
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