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    Subject[PATCH v4 10/12] ima: defer calling __fput()
    Date
    ima_file_free(), which is called on __fput(), updates the file data
    hash stored as an extended attribute to reflect file changes. 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 the __fput() being called until after the mmap_sem is released.

    The number of __fput() calls needing to be deferred is minimal. Only
    those files in policy, that were closed prior to the munmap and were
    mmapped write, need to defer the __fput().

    With this patch, on a clean F16 install, from boot to login, only
    5 out of ~100,000 mmap_sem held fput() calls were deferred.

    Changelog v4:
    - ima_defer_fput() performance improvements
    - move ima_defer_fput() call from remove_vma() to __fput()
    - only defer mmapped files opened for write
    - remove unnecessary ima_fput_mempool_destroy()

    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>
    Signed-off-by: Dmitry Kasatkin <dmitry.kasatkin@intel.com>
    ---
    fs/file_table.c | 5 ++
    include/linux/ima.h | 5 ++
    security/integrity/ima/ima_appraise.c | 81 +++++++++++++++++++++++++++++++++
    3 files changed, 91 insertions(+), 0 deletions(-)

    diff --git a/fs/file_table.c b/fs/file_table.c
    index 554161a..b91f039 100644
    --- a/fs/file_table.c
    +++ b/fs/file_table.c
    @@ -229,6 +229,11 @@ static void __fput(struct file *file)
    struct vfsmount *mnt = file->f_path.mnt;
    struct inode *inode = dentry->d_inode;

    + if (current->mm && rwsem_is_locked(&current->mm->mmap_sem)) {
    + if (ima_defer_fput(file) == 0)
    + return;
    + }
    +
    might_sleep();

    fsnotify_close(file);
    diff --git a/include/linux/ima.h b/include/linux/ima.h
    index 2c7223d..bbfac16 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 int 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 int ima_defer_fput(struct file *file)
    +{
    + return 1;
    +}
    #endif /* CONFIG_IMA_APPRAISE_H */
    #endif /* _LINUX_IMA_H */
    diff --git a/security/integrity/ima/ima_appraise.c b/security/integrity/ima/ima_appraise.c
    index becc7e0..220b20e 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 +227,83 @@ 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.
    + *
    + * Return 0 on success, 1 when unnecessary, or errno on failure.
    + */
    +int 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 result;
    +
    + if (!(file->f_mode & FMODE_WRITE) || !IS_IMA(inode))
    + return 1;
    +
    + defer = mempool_alloc(ima_fput_mempool, GFP_NOIO);
    + if (!defer) /* should never happen */
    + return -ENOMEM;
    +
    + get_file(file);
    +
    + defer->file = file;
    + INIT_WORK(&defer->work, ima_deferred_fput);
    + result = schedule_work(&defer->work);
    + if (result == 0) {
    + pr_info("ima: fput already scheduled\n");
    + mempool_free(defer, ima_fput_mempool);
    + fput_atomic(file);
    + }
    + return 0;
    +}
    +
    +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;
    +}
    +security_initcall(ima_fput_mempool_create);
    --
    1.7.6.5


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