[PATCH -next] user_namespace: Replace gotos with return statements

[PATCH -next] user_namespace: Replace gotos with return statements

[Marcos Paulo de Souza]

Found while inspecting the code that handles the setgroups procfs file.

Signed-off-by: Marcos Paulo de Souza <marcos.souza.org@gmail.com>
---
Tested locally setting up a new userns, and setting setgroups as deny and allow,
worked as before.

 kernel/user_namespace.c | 20 +++++++-------------
 1 file changed, 7 insertions(+), 13 deletions(-)

diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
index 246d4d4ce5c7..64a01254ac6b 100644
--- a/kernel/user_namespace.c
+++ b/kernel/user_namespace.c
@@ -1142,22 +1142,18 @@ ssize_t proc_setgroups_write(struct file *file, const char __user *buf,
 	struct user_namespace *ns = seq->private;
 	char kbuf[8], *pos;
 	bool setgroups_allowed;
-	ssize_t ret;
 
 	/* Only allow a very narrow range of strings to be written */
-	ret = -EINVAL;
 	if ((*ppos != 0) || (count >= sizeof(kbuf)))
-		goto out;
+		return -EINVAL;
 
 	/* What was written? */
-	ret = -EFAULT;
 	if (copy_from_user(kbuf, buf, count))
-		goto out;
+		return -EFAULT;
 	kbuf[count] = '\0';
 	pos = kbuf;
 
 	/* What is being requested? */
-	ret = -EINVAL;
 	if (strncmp(pos, "allow", 5) == 0) {
 		pos += 5;
 		setgroups_allowed = true;
@@ -1167,14 +1163,13 @@ ssize_t proc_setgroups_write(struct file *file, const char __user *buf,
 		setgroups_allowed = false;
 	}
 	else
-		goto out;
+		return -EINVAL;
 
 	/* Verify there is not trailing junk on the line */
 	pos = skip_spaces(pos);
 	if (*pos != '\0')
-		goto out;
+		return -EINVAL;
 
-	ret = -EPERM;
 	mutex_lock(&userns_state_mutex);
 	if (setgroups_allowed) {
 		/* Enabling setgroups after setgroups has been disabled
@@ -1194,12 +1189,11 @@ ssize_t proc_setgroups_write(struct file *file, const char __user *buf,
 
 	/* Report a successful write */
 	*ppos = count;
-	ret = count;
-out:
-	return ret;
+	return count;
+
 out_unlock:
 	mutex_unlock(&userns_state_mutex);
-	goto out;
+	return -EPERM;
 }
 
 bool userns_may_setgroups(const struct user_namespace *ns)
-- 
2.14.3

Re: [PATCH -next] user_namespace: Replace gotos with return statements

[Eric W. Biederman]

Marcos Paulo de Souza <marcos.souza.org@gmail.com> writes:

> Found while inspecting the code that handles the setgroups procfs
> file.

What perchance might be the advantage of introducing multiple exits
into proc_setgroups_write?

I strongly suspect that if you look at the generated code it will
be worse after your patch.


Eric

> Signed-off-by: Marcos Paulo de Souza <marcos.souza.org@gmail.com>
> ---
> Tested locally setting up a new userns, and setting setgroups as deny and allow,
> worked as before.
>
>  kernel/user_namespace.c | 20 +++++++-------------
>  1 file changed, 7 insertions(+), 13 deletions(-)
>
> diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
> index 246d4d4ce5c7..64a01254ac6b 100644
> --- a/kernel/user_namespace.c
> +++ b/kernel/user_namespace.c
> @@ -1142,22 +1142,18 @@ ssize_t proc_setgroups_write(struct file *file, const char __user *buf,
>  	struct user_namespace *ns = seq->private;
>  	char kbuf[8], *pos;
>  	bool setgroups_allowed;
> -	ssize_t ret;
>  
>  	/* Only allow a very narrow range of strings to be written */
> -	ret = -EINVAL;
>  	if ((*ppos != 0) || (count >= sizeof(kbuf)))
> -		goto out;
> +		return -EINVAL;
>  
>  	/* What was written? */
> -	ret = -EFAULT;
>  	if (copy_from_user(kbuf, buf, count))
> -		goto out;
> +		return -EFAULT;
>  	kbuf[count] = '\0';
>  	pos = kbuf;
>  
>  	/* What is being requested? */
> -	ret = -EINVAL;
>  	if (strncmp(pos, "allow", 5) == 0) {
>  		pos += 5;
>  		setgroups_allowed = true;
> @@ -1167,14 +1163,13 @@ ssize_t proc_setgroups_write(struct file *file, const char __user *buf,
>  		setgroups_allowed = false;
>  	}
>  	else
> -		goto out;
> +		return -EINVAL;
>  
>  	/* Verify there is not trailing junk on the line */
>  	pos = skip_spaces(pos);
>  	if (*pos != '\0')
> -		goto out;
> +		return -EINVAL;
>  
> -	ret = -EPERM;
>  	mutex_lock(&userns_state_mutex);
>  	if (setgroups_allowed) {
>  		/* Enabling setgroups after setgroups has been disabled
> @@ -1194,12 +1189,11 @@ ssize_t proc_setgroups_write(struct file *file, const char __user *buf,
>  
>  	/* Report a successful write */
>  	*ppos = count;
> -	ret = count;
> -out:
> -	return ret;
> +	return count;
> +
>  out_unlock:
>  	mutex_unlock(&userns_state_mutex);
> -	goto out;
> +	return -EPERM;
>  }
>  
>  bool userns_may_setgroups(const struct user_namespace *ns)

Re: [PATCH -next] user_namespace: Replace gotos with return statements

[Christian Brauner]

On Wed, Apr 18, 2018 at 11:46:38PM -0300, Marcos Paulo de Souza wrote:
> Found while inspecting the code that handles the setgroups procfs file.

This is not really improving anything so I unfortunately don't really
see why we should take this.

Christian

>
> Signed-off-by: Marcos Paulo de Souza <marcos.souza.org@gmail.com>
> ---
> Tested locally setting up a new userns, and setting setgroups as deny and allow,
> worked as before.
>
>  kernel/user_namespace.c | 20 +++++++-------------
>  1 file changed, 7 insertions(+), 13 deletions(-)
>
> diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
> index 246d4d4ce5c7..64a01254ac6b 100644
> --- a/kernel/user_namespace.c
> +++ b/kernel/user_namespace.c
> @@ -1142,22 +1142,18 @@ ssize_t proc_setgroups_write(struct file *file, const char __user *buf,
>   struct user_namespace *ns = seq->private;
>   char kbuf[8], *pos;
>   bool setgroups_allowed;
> - ssize_t ret;
>
>   /* Only allow a very narrow range of strings to be written */
> - ret = -EINVAL;
>   if ((*ppos != 0) || (count >= sizeof(kbuf)))
> - goto out;
> + return -EINVAL;
>
>   /* What was written? */
> - ret = -EFAULT;
>   if (copy_from_user(kbuf, buf, count))
> - goto out;
> + return -EFAULT;
>   kbuf[count] = '\0';
>   pos = kbuf;
>
>   /* What is being requested? */
> - ret = -EINVAL;
>   if (strncmp(pos, "allow", 5) == 0) {
>   pos += 5;
>   setgroups_allowed = true;
> @@ -1167,14 +1163,13 @@ ssize_t proc_setgroups_write(struct file *file, const char __user *buf,
>   setgroups_allowed = false;
>   }
>   else
> - goto out;
> + return -EINVAL;
>
>   /* Verify there is not trailing junk on the line */
>   pos = skip_spaces(pos);
>   if (*pos != '\0')
> - goto out;
> + return -EINVAL;
>
> - ret = -EPERM;
>   mutex_lock(&userns_state_mutex);
>   if (setgroups_allowed) {
>   /* Enabling setgroups after setgroups has been disabled
> @@ -1194,12 +1189,11 @@ ssize_t proc_setgroups_write(struct file *file, const char __user *buf,
>
>   /* Report a successful write */
>   *ppos = count;
> - ret = count;
> -out:
> - return ret;
> + return count;
> +
>  out_unlock:
>   mutex_unlock(&userns_state_mutex);
> - goto out;
> + return -EPERM;
>  }
>
>  bool userns_may_setgroups(const struct user_namespace *ns)
> --
> 2.14.3
>

Re: [PATCH -next] user_namespace: Replace gotos with return statements

[Marcos Paulo de Souza]

On Wed, May 02, 2018 at 04:12:18PM +0200, Christian Brauner wrote:
> On Wed, Apr 18, 2018 at 11:46:38PM -0300, Marcos Paulo de Souza wrote:
> > Found while inspecting the code that handles the setgroups procfs file.
> 
> This is not really improving anything so I unfortunately don't really
> see why we should take this.

Sorry for the late reply. My idea was to make the code more straightforward,
never happened to me this would led to a worse code being generated. So, please
discard the patch.

Thanks,

> 
> Christian
> 
> >
> > Signed-off-by: Marcos Paulo de Souza <marcos.souza.org@gmail.com>
> > ---
> > Tested locally setting up a new userns, and setting setgroups as deny and allow,
> > worked as before.
> >
> >  kernel/user_namespace.c | 20 +++++++-------------
> >  1 file changed, 7 insertions(+), 13 deletions(-)
> >
> > diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
> > index 246d4d4ce5c7..64a01254ac6b 100644
> > --- a/kernel/user_namespace.c
> > +++ b/kernel/user_namespace.c
> > @@ -1142,22 +1142,18 @@ ssize_t proc_setgroups_write(struct file *file, const char __user *buf,
> >   struct user_namespace *ns = seq->private;
> >   char kbuf[8], *pos;
> >   bool setgroups_allowed;
> > - ssize_t ret;
> >
> >   /* Only allow a very narrow range of strings to be written */
> > - ret = -EINVAL;
> >   if ((*ppos != 0) || (count >= sizeof(kbuf)))
> > - goto out;
> > + return -EINVAL;
> >
> >   /* What was written? */
> > - ret = -EFAULT;
> >   if (copy_from_user(kbuf, buf, count))
> > - goto out;
> > + return -EFAULT;
> >   kbuf[count] = '\0';
> >   pos = kbuf;
> >
> >   /* What is being requested? */
> > - ret = -EINVAL;
> >   if (strncmp(pos, "allow", 5) == 0) {
> >   pos += 5;
> >   setgroups_allowed = true;
> > @@ -1167,14 +1163,13 @@ ssize_t proc_setgroups_write(struct file *file, const char __user *buf,
> >   setgroups_allowed = false;
> >   }
> >   else
> > - goto out;
> > + return -EINVAL;
> >
> >   /* Verify there is not trailing junk on the line */
> >   pos = skip_spaces(pos);
> >   if (*pos != '\0')
> > - goto out;
> > + return -EINVAL;
> >
> > - ret = -EPERM;
> >   mutex_lock(&userns_state_mutex);
> >   if (setgroups_allowed) {
> >   /* Enabling setgroups after setgroups has been disabled
> > @@ -1194,12 +1189,11 @@ ssize_t proc_setgroups_write(struct file *file, const char __user *buf,
> >
> >   /* Report a successful write */
> >   *ppos = count;
> > - ret = count;
> > -out:
> > - return ret;
> > + return count;
> > +
> >  out_unlock:
> >   mutex_unlock(&userns_state_mutex);
> > - goto out;
> > + return -EPERM;
> >  }
> >
> >  bool userns_may_setgroups(const struct user_namespace *ns)
> > --
> > 2.14.3
> >

-- 
Thanks,
	Marcos