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    Subject[PATCH v2 09/11] ima: delay calling __fput()
    Date
    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_delay_fput() increments the f_count
    to delay __fput() being called until after the mmap_sem is released.

    On slab alloc failure, 'security.ima' will be updated, but it would
    be updated immediately, instead of being deferred, causing the
    existing lockdep.

    Changelog:
    - Based on discussions with: Tyler Hicks (use workqueues),
    Dave Hansen (defer only IMA related files), and
    Dmitry Kasatkin (add new IMA hook)
    - use slab for allocating workqueue

    Signed-off-by: Mimi Zohar <zohar@us.ibm.com>
    ---
    include/linux/ima.h | 5 +++
    mm/mmap.c | 1 +
    security/integrity/ima/ima_appraise.c | 60 +++++++++++++++++++++++++++++++++
    3 files changed, 66 insertions(+), 0 deletions(-)

    diff --git a/include/linux/ima.h b/include/linux/ima.h
    index 2c7223d..93b6b37 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_delay_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 void ima_delay_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..95adc72 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_delay_fput(vma->vm_file);
    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 a29eb03..62527e3 100644
    --- a/security/integrity/ima/ima_appraise.c
    +++ b/security/integrity/ima/ima_appraise.c
    @@ -223,3 +223,63 @@ int ima_inode_removexattr(struct dentry *dentry, const char *xattr_name)
    }
    return result;
    }
    +
    +struct wq_info {
    + struct file *file;
    + struct work_struct work;
    +};
    +static struct kmem_cache *wq_cache;
    +
    +static void ima_delayed_fput(struct work_struct *work)
    +{
    + struct wq_info *info = container_of(work, struct wq_info, work);
    +
    + fput(info->file);
    + kmem_cache_free(wq_cache, info);
    +}
    +
    +/**
    + * ima_delay_fput - delay 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 delays calling __fput() until after the mmap_sem is
    + * released.
    + */
    +void ima_delay_fput(struct file *file)
    +{
    + struct dentry *dentry = file->f_path.dentry;
    + struct inode *inode = dentry->d_inode;
    + struct wq_info *info;
    +
    + if (!IS_IMA(inode))
    + return;
    +
    + info = kmem_cache_alloc(wq_cache, GFP_KERNEL);
    + if (!info)
    + return;
    +
    + get_file(file);
    +
    + info->file = file;
    + INIT_WORK(&info->work, ima_delayed_fput);
    + schedule_work(&info->work);
    +}
    +
    +static void init_once(void *foo)
    +{
    + struct wq_info *info = foo;
    +
    + memset(info, 0, sizeof *info);
    +}
    +
    +static int __init ima_wq_cache_init(void)
    +{
    + wq_cache = kmem_cache_create("wq_cache", sizeof(struct wq_info),
    + 0, SLAB_PANIC, init_once);
    + return 0;
    +}
    +security_initcall(ima_wq_cache_init);
    --
    1.7.6.5


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