[PATCH] SUNRPC: Replace strlcpy with strscpy

[PATCH] SUNRPC: Replace strlcpy with strscpy

[Azeem Shaikh]

strlcpy() reads the entire source buffer first.
This read may exceed the destination size limit.
This is both inefficient and can lead to linear read
overflows if a source string is not NUL-terminated [1].
In an effort to remove strlcpy() completely [2], replace
strlcpy() here with strscpy().

Direct replacement is safe here since the getter in kernel_params_ops
handles -errorno return [3].

[1] https://www.kernel.org/doc/html/latest/process/deprecated.html#strlcpy
[2] https://github.com/KSPP/linux/issues/89
[3] https://elixir.bootlin.com/linux/v6.4-rc6/source/include/linux/moduleparam.h#L52

Signed-off-by: Azeem Shaikh <azeemshaikh38@gmail.com>
---
 net/sunrpc/svc.c |    8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/net/sunrpc/svc.c b/net/sunrpc/svc.c
index e6d4cec61e47..e5f379c4fdb3 100644
--- a/net/sunrpc/svc.c
+++ b/net/sunrpc/svc.c
@@ -109,13 +109,13 @@ param_get_pool_mode(char *buf, const struct kernel_param *kp)
 	switch (*ip)
 	{
 	case SVC_POOL_AUTO:
-		return strlcpy(buf, "auto\n", 20);
+		return strscpy(buf, "auto\n", 20);
 	case SVC_POOL_GLOBAL:
-		return strlcpy(buf, "global\n", 20);
+		return strscpy(buf, "global\n", 20);
 	case SVC_POOL_PERCPU:
-		return strlcpy(buf, "percpu\n", 20);
+		return strscpy(buf, "percpu\n", 20);
 	case SVC_POOL_PERNODE:
-		return strlcpy(buf, "pernode\n", 20);
+		return strscpy(buf, "pernode\n", 20);
 	default:
 		return sprintf(buf, "%d\n", *ip);
 	}
-- 
2.41.0.162.gfafddb0af9-goog

Re: [PATCH] SUNRPC: Replace strlcpy with strscpy

[Chuck Lever III]

> On Jun 12, 2023, at 8:40 PM, Azeem Shaikh <azeemshaikh38@gmail.com> wrote:
> 
> strlcpy() reads the entire source buffer first.
> This read may exceed the destination size limit.
> This is both inefficient and can lead to linear read
> overflows if a source string is not NUL-terminated [1].
> In an effort to remove strlcpy() completely [2], replace
> strlcpy() here with strscpy().

Using sprintf() seems cleaner to me: it would get rid of
the undocumented naked integer. Would that work for you?


> Direct replacement is safe here since the getter in kernel_params_ops
> handles -errorno return [3].

s/errorno/errno/


> [1] https://www.kernel.org/doc/html/latest/process/deprecated.html#strlcpy
> [2] https://github.com/KSPP/linux/issues/89
> [3] https://elixir.bootlin.com/linux/v6.4-rc6/source/include/linux/moduleparam.h#L52
> 
> Signed-off-by: Azeem Shaikh <azeemshaikh38@gmail.com>
> ---
> net/sunrpc/svc.c |    8 ++++----
> 1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/net/sunrpc/svc.c b/net/sunrpc/svc.c
> index e6d4cec61e47..e5f379c4fdb3 100644
> --- a/net/sunrpc/svc.c
> +++ b/net/sunrpc/svc.c
> @@ -109,13 +109,13 @@ param_get_pool_mode(char *buf, const struct kernel_param *kp)
> switch (*ip)
> {
> case SVC_POOL_AUTO:
> - return strlcpy(buf, "auto\n", 20);
> + return strscpy(buf, "auto\n", 20);
> case SVC_POOL_GLOBAL:
> - return strlcpy(buf, "global\n", 20);
> + return strscpy(buf, "global\n", 20);
> case SVC_POOL_PERCPU:
> - return strlcpy(buf, "percpu\n", 20);
> + return strscpy(buf, "percpu\n", 20);
> case SVC_POOL_PERNODE:
> - return strlcpy(buf, "pernode\n", 20);
> + return strscpy(buf, "pernode\n", 20);
> default:
> return sprintf(buf, "%d\n", *ip);
> }
> -- 
> 2.41.0.162.gfafddb0af9-goog
> 
> 

--
Chuck Lever

Re: [PATCH] SUNRPC: Replace strlcpy with strscpy

[Kees Cook]

On Tue, Jun 13, 2023 at 02:18:06PM +0000, Chuck Lever III wrote:
> 
> 
> > On Jun 12, 2023, at 8:40 PM, Azeem Shaikh <azeemshaikh38@gmail.com> wrote:
> > 
> > strlcpy() reads the entire source buffer first.
> > This read may exceed the destination size limit.
> > This is both inefficient and can lead to linear read
> > overflows if a source string is not NUL-terminated [1].
> > In an effort to remove strlcpy() completely [2], replace
> > strlcpy() here with strscpy().
> 
> Using sprintf() seems cleaner to me: it would get rid of
> the undocumented naked integer. Would that work for you?

This is changing the "get" routine for reporting module parameters out
of /sys. I think the right choice here is sysfs_emit(), as it performs
the size tracking correctly. (Even the "default" sprintf() call should
be replaced too, IMO.)

> 
> 
> > Direct replacement is safe here since the getter in kernel_params_ops
> > handles -errorno return [3].
> 
> s/errorno/errno/
> 
> 
> > [1] https://www.kernel.org/doc/html/latest/process/deprecated.html#strlcpy
> > [2] https://github.com/KSPP/linux/issues/89
> > [3] https://elixir.bootlin.com/linux/v6.4-rc6/source/include/linux/moduleparam.h#L52
> > 
> > Signed-off-by: Azeem Shaikh <azeemshaikh38@gmail.com>
> > ---
> > net/sunrpc/svc.c |    8 ++++----
> > 1 file changed, 4 insertions(+), 4 deletions(-)
> > 
> > diff --git a/net/sunrpc/svc.c b/net/sunrpc/svc.c
> > index e6d4cec61e47..e5f379c4fdb3 100644
> > --- a/net/sunrpc/svc.c
> > +++ b/net/sunrpc/svc.c
> > @@ -109,13 +109,13 @@ param_get_pool_mode(char *buf, const struct kernel_param *kp)
> > switch (*ip)
> > {
> > case SVC_POOL_AUTO:
> > - return strlcpy(buf, "auto\n", 20);
> > + return strscpy(buf, "auto\n", 20);

e.g.
	return sysfs_emit(buf, "auto\n");
...

> > case SVC_POOL_GLOBAL:
> > - return strlcpy(buf, "global\n", 20);
> > + return strscpy(buf, "global\n", 20);
> > case SVC_POOL_PERCPU:
> > - return strlcpy(buf, "percpu\n", 20);
> > + return strscpy(buf, "percpu\n", 20);
> > case SVC_POOL_PERNODE:
> > - return strlcpy(buf, "pernode\n", 20);
> > + return strscpy(buf, "pernode\n", 20);
> > default:
> > return sprintf(buf, "%d\n", *ip);

and:

	return sysfs_emit(buf, "%d\n", *ip);


-Kees

-- 
Kees Cook

Re: [PATCH] SUNRPC: Replace strlcpy with strscpy

[Chuck Lever III]

> On Jun 13, 2023, at 3:42 PM, Kees Cook <keescook@chromium.org> wrote:
> 
> On Tue, Jun 13, 2023 at 02:18:06PM +0000, Chuck Lever III wrote:
>> 
>> 
>>> On Jun 12, 2023, at 8:40 PM, Azeem Shaikh <azeemshaikh38@gmail.com> wrote:
>>> 
>>> strlcpy() reads the entire source buffer first.
>>> This read may exceed the destination size limit.
>>> This is both inefficient and can lead to linear read
>>> overflows if a source string is not NUL-terminated [1].
>>> In an effort to remove strlcpy() completely [2], replace
>>> strlcpy() here with strscpy().
>> 
>> Using sprintf() seems cleaner to me: it would get rid of
>> the undocumented naked integer. Would that work for you?
> 
> This is changing the "get" routine for reporting module parameters out
> of /sys. I think the right choice here is sysfs_emit(), as it performs
> the size tracking correctly. (Even the "default" sprintf() call should
> be replaced too, IMO.)

Agreed, that's even better.


>>> Direct replacement is safe here since the getter in kernel_params_ops
>>> handles -errorno return [3].
>> 
>> s/errorno/errno/
>> 
>> 
>>> [1] https://www.kernel.org/doc/html/latest/process/deprecated.html#strlcpy
>>> [2] https://github.com/KSPP/linux/issues/89
>>> [3] https://elixir.bootlin.com/linux/v6.4-rc6/source/include/linux/moduleparam.h#L52
>>> 
>>> Signed-off-by: Azeem Shaikh <azeemshaikh38@gmail.com>
>>> ---
>>> net/sunrpc/svc.c |    8 ++++----
>>> 1 file changed, 4 insertions(+), 4 deletions(-)
>>> 
>>> diff --git a/net/sunrpc/svc.c b/net/sunrpc/svc.c
>>> index e6d4cec61e47..e5f379c4fdb3 100644
>>> --- a/net/sunrpc/svc.c
>>> +++ b/net/sunrpc/svc.c
>>> @@ -109,13 +109,13 @@ param_get_pool_mode(char *buf, const struct kernel_param *kp)
>>> switch (*ip)
>>> {
>>> case SVC_POOL_AUTO:
>>> - return strlcpy(buf, "auto\n", 20);
>>> + return strscpy(buf, "auto\n", 20);
> 
> e.g.
> return sysfs_emit(buf, "auto\n");
> ...
> 
>>> case SVC_POOL_GLOBAL:
>>> - return strlcpy(buf, "global\n", 20);
>>> + return strscpy(buf, "global\n", 20);
>>> case SVC_POOL_PERCPU:
>>> - return strlcpy(buf, "percpu\n", 20);
>>> + return strscpy(buf, "percpu\n", 20);
>>> case SVC_POOL_PERNODE:
>>> - return strlcpy(buf, "pernode\n", 20);
>>> + return strscpy(buf, "pernode\n", 20);
>>> default:
>>> return sprintf(buf, "%d\n", *ip);
> 
> and:
> 
> return sysfs_emit(buf, "%d\n", *ip);
> 
> 
> -Kees
> 
> -- 
> Kees Cook


--
Chuck Lever

Re: [PATCH] SUNRPC: Replace strlcpy with strscpy

[Azeem Shaikh]

On Tue, Jun 13, 2023 at 3:43 PM Chuck Lever III <chuck.lever@oracle.com> wrote:
>
> > On Jun 13, 2023, at 3:42 PM, Kees Cook <keescook@chromium.org> wrote:
> >
> > On Tue, Jun 13, 2023 at 02:18:06PM +0000, Chuck Lever III wrote:
> >>
> >>
> >>> On Jun 12, 2023, at 8:40 PM, Azeem Shaikh <azeemshaikh38@gmail.com> wrote:
> >>>
> >>> strlcpy() reads the entire source buffer first.
> >>> This read may exceed the destination size limit.
> >>> This is both inefficient and can lead to linear read
> >>> overflows if a source string is not NUL-terminated [1].
> >>> In an effort to remove strlcpy() completely [2], replace
> >>> strlcpy() here with strscpy().
> >>
> >> Using sprintf() seems cleaner to me: it would get rid of
> >> the undocumented naked integer. Would that work for you?
> >
> > This is changing the "get" routine for reporting module parameters out
> > of /sys. I think the right choice here is sysfs_emit(), as it performs
> > the size tracking correctly. (Even the "default" sprintf() call should
> > be replaced too, IMO.)
>
> Agreed, that's even better.
>

Thanks folks. Will send over a v2 which replaces strlcpy with sysfs_emit.