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proc: save 2 atomic ops on write to "/proc/*/attr/*" 

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.

Link: http://lkml.kernel.org/r/20180627200218.GF18113@avx2
Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
hifive-unleashed-5.1
Alexey Dobriyan 2018-08-21 21:54:30 -07:00 committed by Linus Torvalds
parent a44937fe4e
commit 41089b6d3e
1 changed files with 19 additions and 19 deletions
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38
fs/proc/base.c
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@ -2517,47 +2517,47 @@ static ssize_t proc_pid_attr_write(struct file * file, const char __user * buf,
size_t count, loff_t *ppos) size_t count, loff_t *ppos)
{ {
struct inode * inode = file_inode(file); struct inode * inode = file_inode(file);
struct task_struct *task;
void *page; void *page;
ssize_t length; int rv;
struct task_struct *task = get_proc_task(inode);
length = -ESRCH;
if (!task)
goto out_no_task;
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. */ /* A task may only write its own attributes. */
length = -EACCES; if (current != task) {
if (current != task) rcu_read_unlock();
goto out; return -EACCES;
}
rcu_read_unlock();
if (count > PAGE_SIZE) if (count > PAGE_SIZE)
count = PAGE_SIZE; count = PAGE_SIZE;
/* No partial writes. */ /* No partial writes. */
length = -EINVAL;
if (*ppos != 0) if (*ppos != 0)
goto out; return -EINVAL;
page = memdup_user(buf, count); page = memdup_user(buf, count);
if (IS_ERR(page)) { if (IS_ERR(page)) {
length = PTR_ERR(page); rv = PTR_ERR(page);
goto out; goto out;
} }
/* Guard against adverse ptrace interaction */ /* Guard against adverse ptrace interaction */
length = mutex_lock_interruptible(&current->signal->cred_guard_mutex); rv = mutex_lock_interruptible(&current->signal->cred_guard_mutex);
if (length < 0) if (rv < 0)
goto out_free; goto out_free;
length = security_setprocattr(file->f_path.dentry->d_name.name, rv = security_setprocattr(file->f_path.dentry->d_name.name, page, count);
page, count);
mutex_unlock(&current->signal->cred_guard_mutex); mutex_unlock(&current->signal->cred_guard_mutex);
out_free: out_free:
kfree(page); kfree(page);
out: out:
put_task_struct(task); return rv;
out_no_task:
return length;
} }
static const struct file_operations proc_pid_attr_operations = { static const struct file_operations proc_pid_attr_operations = {