[PATCH] NFSD: Replace all non-returning strlcpy with strscpy

[PATCH] NFSD: Replace all non-returning 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().
No return values were used, so direct replacement is safe.

[1] https://www.kernel.org/doc/html/latest/process/deprecated.html#strlcpy
[2] https://github.com/KSPP/linux/issues/89

Signed-off-by: Azeem Shaikh <azeemshaikh38@gmail.com>
---
 fs/nfsd/trace.h |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/nfsd/trace.h b/fs/nfsd/trace.h
index 4183819ea082..9b32cda54808 100644
--- a/fs/nfsd/trace.h
+++ b/fs/nfsd/trace.h
@@ -1370,7 +1370,7 @@ TRACE_EVENT(nfsd_cb_setup,
 	TP_fast_assign(
 		__entry->cl_boot = clp->cl_clientid.cl_boot;
 		__entry->cl_id = clp->cl_clientid.cl_id;
-		strlcpy(__entry->netid, netid, sizeof(__entry->netid));
+		strscpy(__entry->netid, netid, sizeof(__entry->netid));
 		__entry->authflavor = authflavor;
 		__assign_sockaddr(addr, &clp->cl_cb_conn.cb_addr,
 				  clp->cl_cb_conn.cb_addrlen)

Re: [PATCH] NFSD: Replace all non-returning strlcpy with strscpy

[Chuck Lever III]

Hello Azeem -

> On May 10, 2023, at 3:09 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().
> No return values were used, so direct replacement is safe.

Actually netid should use the __string() and __assign_str()
macros rather than open-coding a string copy, I think.


> [1] https://www.kernel.org/doc/html/latest/process/deprecated.html#strlcpy
> [2] https://github.com/KSPP/linux/issues/89
> 

I suggest adding:

Fixes: 3c92fba557c6 ("NFSD: Enhance the nfsd_cb_setup tracepoint")

> Signed-off-by: Azeem Shaikh <azeemshaikh38@gmail.com>
> ---
> fs/nfsd/trace.h |    2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/nfsd/trace.h b/fs/nfsd/trace.h
> index 4183819ea082..9b32cda54808 100644
> --- a/fs/nfsd/trace.h
> +++ b/fs/nfsd/trace.h
> @@ -1370,7 +1370,7 @@ TRACE_EVENT(nfsd_cb_setup,
> TP_fast_assign(
> __entry->cl_boot = clp->cl_clientid.cl_boot;
> __entry->cl_id = clp->cl_clientid.cl_id;
> - strlcpy(__entry->netid, netid, sizeof(__entry->netid));
> + strscpy(__entry->netid, netid, sizeof(__entry->netid));
> __entry->authflavor = authflavor;
> __assign_sockaddr(addr, &clp->cl_cb_conn.cb_addr,
>  clp->cl_cb_conn.cb_addrlen)
> 

--
Chuck Lever

Re: [PATCH] NFSD: Replace all non-returning strlcpy with strscpy

[Kees Cook]

On Thu, May 11, 2023 at 02:47:54PM +0000, Chuck Lever III wrote:
> Hello Azeem -
> 
> > On May 10, 2023, at 3:09 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().
> > No return values were used, so direct replacement is safe.
> 
> Actually netid should use the __string() and __assign_str()
> macros rather than open-coding a string copy, I think.

Ah, hm, yeah, this is tracing wrappers.

Steve, is there a reason __assign_str() is using "strcpy" and not
strscpy()?

> Fixes: 3c92fba557c6 ("NFSD: Enhance the nfsd_cb_setup tracepoint")

Yeah, that works. I was on the fence about adding Fixes for these kinds
of refactoring. Like, it's not really _broken_; we're just trying to
remove the API.

> > Signed-off-by: Azeem Shaikh <azeemshaikh38@gmail.com>
> > ---
> > fs/nfsd/trace.h |    2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/fs/nfsd/trace.h b/fs/nfsd/trace.h
> > index 4183819ea082..9b32cda54808 100644
> > --- a/fs/nfsd/trace.h
> > +++ b/fs/nfsd/trace.h
> > @@ -1370,7 +1370,7 @@ TRACE_EVENT(nfsd_cb_setup,
> > TP_fast_assign(
> > __entry->cl_boot = clp->cl_clientid.cl_boot;
> > __entry->cl_id = clp->cl_clientid.cl_id;
> > - strlcpy(__entry->netid, netid, sizeof(__entry->netid));
> > + strscpy(__entry->netid, netid, sizeof(__entry->netid));
> > __entry->authflavor = authflavor;
> > __assign_sockaddr(addr, &clp->cl_cb_conn.cb_addr,
> >  clp->cl_cb_conn.cb_addrlen)

Leaving code context for Steve to see...

-- 
Kees Cook

Re: [PATCH] NFSD: Replace all non-returning strlcpy with strscpy

[Azeem Shaikh]

Thanks Chuck and Kees for the review.

> > Actually netid should use the __string() and __assign_str()
> > macros rather than open-coding a string copy, I think.

Do you mean something like this?

diff --git a/fs/nfsd/trace.h b/fs/nfsd/trace.h
index 4183819ea082..72a906a053dc 100644
--- a/fs/nfsd/trace.h
+++ b/fs/nfsd/trace.h
@@ -1365,19 +1365,19 @@ TRACE_EVENT(nfsd_cb_setup,
                __field(u32, cl_id)
                __field(unsigned long, authflavor)
                __sockaddr(addr, clp->cl_cb_conn.cb_addrlen)
-               __array(unsigned char, netid, 8)
+               __string(netid, netid)
        ),
        TP_fast_assign(
                __entry->cl_boot = clp->cl_clientid.cl_boot;
                __entry->cl_id = clp->cl_clientid.cl_id;
-               strlcpy(__entry->netid, netid, sizeof(__entry->netid));
+               __assign_str(netid, netid);
                __entry->authflavor = authflavor;
                __assign_sockaddr(addr, &clp->cl_cb_conn.cb_addr,
                                  clp->cl_cb_conn.cb_addrlen)
        ),
        TP_printk("addr=%pISpc client %08x:%08x proto=%s flavor=%s",
                __get_sockaddr(addr), __entry->cl_boot, __entry->cl_id,
-               __entry->netid, show_nfsd_authflavor(__entry->authflavor))
+               __get_str(netid), show_nfsd_authflavor(__entry->authflavor))
 );

> > Fixes: 3c92fba557c6 ("NFSD: Enhance the nfsd_cb_setup tracepoint")

Ack.

Re: [PATCH] NFSD: Replace all non-returning strlcpy with strscpy

[Chuck Lever III]

> On May 12, 2023, at 7:30 AM, Azeem Shaikh <azeemshaikh38@gmail.com> wrote:
> 
> Thanks Chuck and Kees for the review.
> 
>>> Actually netid should use the __string() and __assign_str()
>>> macros rather than open-coding a string copy, I think.
> 
> Do you mean something like this?
> 
> diff --git a/fs/nfsd/trace.h b/fs/nfsd/trace.h
> index 4183819ea082..72a906a053dc 100644
> --- a/fs/nfsd/trace.h
> +++ b/fs/nfsd/trace.h
> @@ -1365,19 +1365,19 @@ TRACE_EVENT(nfsd_cb_setup,
>                __field(u32, cl_id)
>                __field(unsigned long, authflavor)
>                __sockaddr(addr, clp->cl_cb_conn.cb_addrlen)
> -               __array(unsigned char, netid, 8)
> +               __string(netid, netid)
>        ),
>        TP_fast_assign(
>                __entry->cl_boot = clp->cl_clientid.cl_boot;
>                __entry->cl_id = clp->cl_clientid.cl_id;
> -               strlcpy(__entry->netid, netid, sizeof(__entry->netid));
> +               __assign_str(netid, netid);
>                __entry->authflavor = authflavor;
>                __assign_sockaddr(addr, &clp->cl_cb_conn.cb_addr,
>                                  clp->cl_cb_conn.cb_addrlen)
>        ),
>        TP_printk("addr=%pISpc client %08x:%08x proto=%s flavor=%s",
>                __get_sockaddr(addr), __entry->cl_boot, __entry->cl_id,
> -               __entry->netid, show_nfsd_authflavor(__entry->authflavor))
> +               __get_str(netid), show_nfsd_authflavor(__entry->authflavor))
> );

Yes. I don't remember why I chose to open-code the string
handling in here.

I agree with Kees, also: __assign_str() needs to handle
the memory accesses properly, and I had assumed it did
that already. My bad. That IMO should be handled as a
separate patch.


>>> Fixes: 3c92fba557c6 ("NFSD: Enhance the nfsd_cb_setup tracepoint")
> 
> Ack.

I agree that it's not a high priority backport. However,
I expect those who want to use trace points on KASAN-
enabled stable kernels might prefer to have the
__assign_str fix in place, along with this one.

So, I'm good with including Fixes: or leaving it off. Up
to you!

--
Chuck Lever

Re: [PATCH] NFSD: Replace all non-returning strlcpy with strscpy

[Azeem Shaikh]

On Fri, May 12, 2023 at 10:38 AM Chuck Lever III <chuck.lever@oracle.com> wrote:
>
>
>
> > On May 12, 2023, at 7:30 AM, Azeem Shaikh <azeemshaikh38@gmail.com> wrote:
> >
> > Thanks Chuck and Kees for the review.
> >
> >>> Actually netid should use the __string() and __assign_str()
> >>> macros rather than open-coding a string copy, I think.
> >
> > Do you mean something like this?
> >
> > diff --git a/fs/nfsd/trace.h b/fs/nfsd/trace.h
> > index 4183819ea082..72a906a053dc 100644
> > --- a/fs/nfsd/trace.h
> > +++ b/fs/nfsd/trace.h
> > @@ -1365,19 +1365,19 @@ TRACE_EVENT(nfsd_cb_setup,
> >                __field(u32, cl_id)
> >                __field(unsigned long, authflavor)
> >                __sockaddr(addr, clp->cl_cb_conn.cb_addrlen)
> > -               __array(unsigned char, netid, 8)
> > +               __string(netid, netid)
> >        ),
> >        TP_fast_assign(
> >                __entry->cl_boot = clp->cl_clientid.cl_boot;
> >                __entry->cl_id = clp->cl_clientid.cl_id;
> > -               strlcpy(__entry->netid, netid, sizeof(__entry->netid));
> > +               __assign_str(netid, netid);
> >                __entry->authflavor = authflavor;
> >                __assign_sockaddr(addr, &clp->cl_cb_conn.cb_addr,
> >                                  clp->cl_cb_conn.cb_addrlen)
> >        ),
> >        TP_printk("addr=%pISpc client %08x:%08x proto=%s flavor=%s",
> >                __get_sockaddr(addr), __entry->cl_boot, __entry->cl_id,
> > -               __entry->netid, show_nfsd_authflavor(__entry->authflavor))
> > +               __get_str(netid), show_nfsd_authflavor(__entry->authflavor))
> > );
>
> Yes. I don't remember why I chose to open-code the string
> handling in here.
>
> I agree with Kees, also: __assign_str() needs to handle
> the memory accesses properly, and I had assumed it did
> that already. My bad. That IMO should be handled as a
> separate patch.

Thanks I'll send out a patch with the __assign_str replacement for now.
I'll wait for Kees and Steve to respond on how to fix the memory
access in __assign_str.

> >>> Fixes: 3c92fba557c6 ("NFSD: Enhance the nfsd_cb_setup tracepoint")
> >
> > Ack.
>
> I agree that it's not a high priority backport. However,
> I expect those who want to use trace points on KASAN-
> enabled stable kernels might prefer to have the
> __assign_str fix in place, along with this one.
>
> So, I'm good with including Fixes: or leaving it off. Up
> to you!
>

Will include it :)

Re: [PATCH] NFSD: Replace all non-returning strlcpy with strscpy

[Steven Rostedt]

On Thu, 11 May 2023 09:32:31 -0700
Kees Cook <keescook@chromium.org> wrote:

> On Thu, May 11, 2023 at 02:47:54PM +0000, Chuck Lever III wrote:
> > Hello Azeem -
> >   
> > > On May 10, 2023, at 3:09 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().
> > > No return values were used, so direct replacement is safe.  
> > 
> > Actually netid should use the __string() and __assign_str()
> > macros rather than open-coding a string copy, I think.  
> 
> Ah, hm, yeah, this is tracing wrappers.
> 
> Steve, is there a reason __assign_str() is using "strcpy" and not
> strscpy()?

Yes. Because __assign_str() predates strscpy() ;-)

Note, to use __assign_str(), you first need to do __string(), which
will do (in all that TRACE_EVENT() macro magic):

#undef __dynamic_array
#define __dynamic_array(type, item, len)                                \
        __item_length = (len) * sizeof(type);                           \
        __data_offsets->item = __data_size +                            \
                               offsetof(typeof(*entry), __data);        \
        __data_offsets->item |= __item_length << 16;                    \
        __data_size += __item_length;

#undef __string
#define __string(item, src) __dynamic_array(char, item,                 \
                    strlen((src) ? (const char *)(src) : "(null)") + 1)

In order to save a dynamic size string (or array) it must first
calculate that size with a strlen(). If the source is not terminated,
then this will crash there regardless.

The strlen() is to know how much to allocate on the ring buffer, then a
copy is done to copy it. I guess you could be worried about the size
"changing" between the time it is allocated and copied. If that's the
concern then we could do a length copy.

> 
> > Fixes: 3c92fba557c6 ("NFSD: Enhance the nfsd_cb_setup tracepoint")  
> 
> Yeah, that works. I was on the fence about adding Fixes for these kinds
> of refactoring. Like, it's not really _broken_; we're just trying to
> remove the API.
> 
> > > Signed-off-by: Azeem Shaikh <azeemshaikh38@gmail.com>
> > > ---
> > > fs/nfsd/trace.h |    2 +-
> > > 1 file changed, 1 insertion(+), 1 deletion(-)
> > > 
> > > diff --git a/fs/nfsd/trace.h b/fs/nfsd/trace.h
> > > index 4183819ea082..9b32cda54808 100644
> > > --- a/fs/nfsd/trace.h
> > > +++ b/fs/nfsd/trace.h
> > > @@ -1370,7 +1370,7 @@ TRACE_EVENT(nfsd_cb_setup,
> > > TP_fast_assign(
> > > __entry->cl_boot = clp->cl_clientid.cl_boot;
> > > __entry->cl_id = clp->cl_clientid.cl_id;
> > > - strlcpy(__entry->netid, netid, sizeof(__entry->netid));
> > > + strscpy(__entry->netid, netid, sizeof(__entry->netid));
> > > __entry->authflavor = authflavor;
> > > __assign_sockaddr(addr, &clp->cl_cb_conn.cb_addr,
> > >  clp->cl_cb_conn.cb_addrlen)  
> 
> Leaving code context for Steve to see...
> 

The above isn't __assign_str(). Not exactly sure what you want me to
see here.

-- Steve