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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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