[PATCH 01/14] sysctl: provide callback for write into ctl_table entry

[Sasha Levin <levinsasha928@gmail.com>]

Provide a callback that will be called when writing to a ctl_table
entry after the user input has been validated.

This will simplify user input checks since now it will be possible to
remove them out of the proc_handler.

Signed-off-by: Sasha Levin <levinsasha928@gmail.com>
---
 fs/proc/proc_sysctl.c  |    4 ++++
 include/linux/sysctl.h |    1 +
 2 files changed, 5 insertions(+), 0 deletions(-)

diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c
index 21d836f..190db28 100644
--- a/fs/proc/proc_sysctl.c
+++ b/fs/proc/proc_sysctl.c
@@ -507,6 +507,10 @@ static ssize_t proc_sys_call_handler(struct file *filp, void __user *buf,
 	error = table->proc_handler(table, write, buf, &res, ppos);
 	if (!error)
 		error = res;
+
+	if (!error && write && table->callback)
+		error = table->callback();
+
 out:
 	sysctl_head_finish(head);
 
diff --git a/include/linux/sysctl.h b/include/linux/sysctl.h
index c34b4c8..27c14cf 100644
--- a/include/linux/sysctl.h
+++ b/include/linux/sysctl.h
@@ -1022,6 +1022,7 @@ struct ctl_table
 	struct ctl_table_poll *poll;
 	void *extra1;
 	void *extra2;
+	int (*callback)(void);		/* Called when entry is written to */
 };
 
 struct ctl_node {
-- 
1.7.8.5

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