This introduces a function which can be used to fetch a file, given an
arbitrary task. As long as the user holds a reference (refcnt) to the
task_struct it is safe to call, and will either return NULL on failure,
or a pointer to the file, with a refcnt.
Signed-off-by: Sargun Dhillon <sargun@xxxxxxxxx>
---
fs/file.c | 19 +++++++++++++++++++
include/linux/fdtable.h | 10 ++++++++++
2 files changed, 29 insertions(+)
diff --git a/fs/file.c b/fs/file.c
index 3da91a112bab..98601a503a0f 100644
--- a/fs/file.c
+++ b/fs/file.c
@@ -1015,3 +1015,22 @@ int iterate_fd(struct files_struct *files, unsigned n,
return res;
}
EXPORT_SYMBOL(iterate_fd);
+
+struct file *get_task_file(struct task_struct *task, unsigned int fd)
+{
+ struct file *file = NULL;
+
+ task_lock(task);
+ rcu_read_lock();
+
+ if (task->files) {
+ file = fcheck_files(task->files, fd);
+ if (file && !get_file_rcu(file))
+ file = NULL;
+ }
+
+ rcu_read_unlock();
+ task_unlock(task);
+
+ return file;
+}
diff --git a/include/linux/fdtable.h b/include/linux/fdtable.h
index f07c55ea0c22..eacb1a56df44 100644
--- a/include/linux/fdtable.h
+++ b/include/linux/fdtable.h
@@ -115,6 +115,16 @@ int iterate_fd(struct files_struct *, unsigned,
int (*)(const void *, struct file *, unsigned),
const void *);
+/*
+ * get_task_file - get a reference to a file from another task
+ * @task: the task to get the file descriptor from
+ * @fd: the file descriptor number to fetch
+ *
+ * returns NULL on failure, or pointer to the file on success, with a reference
+ * It requires that the task is pinned prior to calling it.
+ */
+struct file *get_task_file(struct task_struct *task, unsigned int fd);
+
extern int __alloc_fd(struct files_struct *files,
unsigned start, unsigned end, unsigned flags);
extern void __fd_install(struct files_struct *files,
--
2.20.1
