[PATCH] proc: save 2 atomic ops on write to "/proc/*/attr/*"
From: Alexey Dobriyan
Date: Wed Jun 27 2018 - 16:02:29 EST
Code checks if write is done by current to its own attributes.
For that get/put pair is unnecessary as it can be done under RCU.
Note: rcu_read_unlock() can be done even earlier since pointer to a task
is not dereferenced. It depends if /proc code should look scary or not:
rcu_read_lock();
task = pid_task(...);
rcu_read_unlock();
if (!task)
return -ESRCH;
if (task != current)
return -EACCESS:
P.S.: rename "length" variable. Code like this
length = -EINVAL;
should not exist.
Signed-off-by: Alexey Dobriyan <adobriyan@xxxxxxxxx>
---
fs/proc/base.c | 38 +++++++++++++++++++-------------------
1 file changed, 19 insertions(+), 19 deletions(-)
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -2517,47 +2517,47 @@ static ssize_t proc_pid_attr_write(struct file * file, const char __user * buf,
size_t count, loff_t *ppos)
{
struct inode * inode = file_inode(file);
+ struct task_struct *task;
void *page;
- ssize_t length;
- struct task_struct *task = get_proc_task(inode);
-
- length = -ESRCH;
- if (!task)
- goto out_no_task;
+ int rv;
+ rcu_read_lock();
+ task = pid_task(proc_pid(inode), PIDTYPE_PID);
+ if (!task) {
+ rcu_read_unlock();
+ return -ESRCH;
+ }
/* A task may only write its own attributes. */
- length = -EACCES;
- if (current != task)
- goto out;
+ if (current != task) {
+ rcu_read_unlock();
+ return -EACCES;
+ }
+ rcu_read_unlock();
if (count > PAGE_SIZE)
count = PAGE_SIZE;
/* No partial writes. */
- length = -EINVAL;
if (*ppos != 0)
- goto out;
+ return -EINVAL;
page = memdup_user(buf, count);
if (IS_ERR(page)) {
- length = PTR_ERR(page);
+ rv = PTR_ERR(page);
goto out;
}
/* Guard against adverse ptrace interaction */
- length = mutex_lock_interruptible(¤t->signal->cred_guard_mutex);
- if (length < 0)
+ rv = mutex_lock_interruptible(¤t->signal->cred_guard_mutex);
+ if (rv < 0)
goto out_free;
- length = security_setprocattr(file->f_path.dentry->d_name.name,
- page, count);
+ rv = security_setprocattr(file->f_path.dentry->d_name.name, page, count);
mutex_unlock(¤t->signal->cred_guard_mutex);
out_free:
kfree(page);
out:
- put_task_struct(task);
-out_no_task:
- return length;
+ return rv;
}
static const struct file_operations proc_pid_attr_operations = {