[PATCH] sunrpc: Avoid a KASAN slab-out-of-bounds bug in xdr_set_page_base()

[PATCH] sunrpc: Avoid a KASAN slab-out-of-bounds bug in xdr_set_page_base()

[schumaker.anna]

From: Anna Schumaker <Anna.Schumaker@Netapp.com>

This seems to happen fairly easily during READ_PLUS testing on NFS v4.2.
I found that we could end up accessing xdr->buf->pages[pgnr] with a pgnr
greater than the number of pages in the array. So let's just return
early if we're setting base to a point at the end of the page data and
let xdr_set_tail_base() handle setting up the buffer pointers instead.

Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
---
 net/sunrpc/xdr.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/net/sunrpc/xdr.c b/net/sunrpc/xdr.c
index 3964ff74ee51..ca10ba2626f2 100644
--- a/net/sunrpc/xdr.c
+++ b/net/sunrpc/xdr.c
@@ -1230,10 +1230,9 @@ static unsigned int xdr_set_page_base(struct xdr_stream *xdr,
 	void *kaddr;
 
 	maxlen = xdr->buf->page_len;
-	if (base >= maxlen) {
-		base = maxlen;
-		maxlen = 0;
-	} else
+	if (base >= maxlen)
+		return 0;
+	else
 		maxlen -= base;
 	if (len > maxlen)
 		len = maxlen;
-- 
2.32.0

Re: [PATCH] sunrpc: Avoid a KASAN slab-out-of-bounds bug in xdr_set_page_base()

[J. Bruce Fields]

On Wed, Jun 09, 2021 at 05:07:29PM -0400, schumaker.anna@gmail.com wrote:
> From: Anna Schumaker <Anna.Schumaker@Netapp.com>
> 
> This seems to happen fairly easily during READ_PLUS testing on NFS v4.2.

Yep, I hit a KASAN warning here every time, and this fixes it,
thanks.--b.

> I found that we could end up accessing xdr->buf->pages[pgnr] with a pgnr
> greater than the number of pages in the array. So let's just return
> early if we're setting base to a point at the end of the page data and
> let xdr_set_tail_base() handle setting up the buffer pointers instead.
> 
> Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
> ---
>  net/sunrpc/xdr.c | 7 +++----
>  1 file changed, 3 insertions(+), 4 deletions(-)
> 
> diff --git a/net/sunrpc/xdr.c b/net/sunrpc/xdr.c
> index 3964ff74ee51..ca10ba2626f2 100644
> --- a/net/sunrpc/xdr.c
> +++ b/net/sunrpc/xdr.c
> @@ -1230,10 +1230,9 @@ static unsigned int xdr_set_page_base(struct xdr_stream *xdr,
>  	void *kaddr;
>  
>  	maxlen = xdr->buf->page_len;
> -	if (base >= maxlen) {
> -		base = maxlen;
> -		maxlen = 0;
> -	} else
> +	if (base >= maxlen)
> +		return 0;
> +	else
>  		maxlen -= base;
>  	if (len > maxlen)
>  		len = maxlen;
> -- 
> 2.32.0

Re: [PATCH] sunrpc: Avoid a KASAN slab-out-of-bounds bug in xdr_set_page_base()

[J. Bruce Fields]

On Mon, Jun 14, 2021 at 07:14:40PM -0400, bfields wrote:
> On Wed, Jun 09, 2021 at 05:07:29PM -0400, schumaker.anna@gmail.com wrote:
> > From: Anna Schumaker <Anna.Schumaker@Netapp.com>
> > 
> > This seems to happen fairly easily during READ_PLUS testing on NFS v4.2.
> 
> Yep, I hit a KASAN warning here every time, and this fixes it,
> thanks.--b.

By the way, config NFS_V4_2_READ_PLUS still says:

	This is intended for developers only. The READ_PLUS operation
	has been shown to have issues under specific conditions and
	should not be used in production.

But this warning was the only thing I was seeing.  Is there another
known issue remaining?

--b.

> 
> > I found that we could end up accessing xdr->buf->pages[pgnr] with a pgnr
> > greater than the number of pages in the array. So let's just return
> > early if we're setting base to a point at the end of the page data and
> > let xdr_set_tail_base() handle setting up the buffer pointers instead.
> > 
> > Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
> > ---
> >  net/sunrpc/xdr.c | 7 +++----
> >  1 file changed, 3 insertions(+), 4 deletions(-)
> > 
> > diff --git a/net/sunrpc/xdr.c b/net/sunrpc/xdr.c
> > index 3964ff74ee51..ca10ba2626f2 100644
> > --- a/net/sunrpc/xdr.c
> > +++ b/net/sunrpc/xdr.c
> > @@ -1230,10 +1230,9 @@ static unsigned int xdr_set_page_base(struct xdr_stream *xdr,
> >  	void *kaddr;
> >  
> >  	maxlen = xdr->buf->page_len;
> > -	if (base >= maxlen) {
> > -		base = maxlen;
> > -		maxlen = 0;
> > -	} else
> > +	if (base >= maxlen)
> > +		return 0;
> > +	else
> >  		maxlen -= base;
> >  	if (len > maxlen)
> >  		len = maxlen;
> > -- 
> > 2.32.0

Re: [PATCH] sunrpc: Avoid a KASAN slab-out-of-bounds bug in xdr_set_page_base()

[Anna Schumaker]

On Thu, Aug 12, 2021 at 4:32 PM J. Bruce Fields <bfields@fieldses.org> wrote:
>
> On Mon, Jun 14, 2021 at 07:14:40PM -0400, bfields wrote:
> > On Wed, Jun 09, 2021 at 05:07:29PM -0400, schumaker.anna@gmail.com wrote:
> > > From: Anna Schumaker <Anna.Schumaker@Netapp.com>
> > >
> > > This seems to happen fairly easily during READ_PLUS testing on NFS v4.2.
> >
> > Yep, I hit a KASAN warning here every time, and this fixes it,
> > thanks.--b.
>
> By the way, config NFS_V4_2_READ_PLUS still says:
>
>         This is intended for developers only. The READ_PLUS operation
>         has been shown to have issues under specific conditions and
>         should not be used in production.
>
> But this warning was the only thing I was seeing.  Is there another
> known issue remaining?

I think it was an issue around using lseek to generate the reply. The
file contents could change between each call, leading to inconsistent
results (and a new failing xfstest that previously passed)

Anna

>
> --b.
>
> >
> > > I found that we could end up accessing xdr->buf->pages[pgnr] with a pgnr
> > > greater than the number of pages in the array. So let's just return
> > > early if we're setting base to a point at the end of the page data and
> > > let xdr_set_tail_base() handle setting up the buffer pointers instead.
> > >
> > > Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
> > > ---
> > >  net/sunrpc/xdr.c | 7 +++----
> > >  1 file changed, 3 insertions(+), 4 deletions(-)
> > >
> > > diff --git a/net/sunrpc/xdr.c b/net/sunrpc/xdr.c
> > > index 3964ff74ee51..ca10ba2626f2 100644
> > > --- a/net/sunrpc/xdr.c
> > > +++ b/net/sunrpc/xdr.c
> > > @@ -1230,10 +1230,9 @@ static unsigned int xdr_set_page_base(struct xdr_stream *xdr,
> > >     void *kaddr;
> > >
> > >     maxlen = xdr->buf->page_len;
> > > -   if (base >= maxlen) {
> > > -           base = maxlen;
> > > -           maxlen = 0;
> > > -   } else
> > > +   if (base >= maxlen)
> > > +           return 0;
> > > +   else
> > >             maxlen -= base;
> > >     if (len > maxlen)
> > >             len = maxlen;
> > > --
> > > 2.32.0

Re: [PATCH] sunrpc: Avoid a KASAN slab-out-of-bounds bug in xdr_set_page_base()

[J. Bruce Fields]

On Thu, Aug 26, 2021 at 03:44:32PM -0400, Anna Schumaker wrote:
> On Thu, Aug 12, 2021 at 4:32 PM J. Bruce Fields <bfields@fieldses.org> wrote:
> >
> > On Mon, Jun 14, 2021 at 07:14:40PM -0400, bfields wrote:
> > > On Wed, Jun 09, 2021 at 05:07:29PM -0400, schumaker.anna@gmail.com wrote:
> > > > From: Anna Schumaker <Anna.Schumaker@Netapp.com>
> > > >
> > > > This seems to happen fairly easily during READ_PLUS testing on NFS v4.2.
> > >
> > > Yep, I hit a KASAN warning here every time, and this fixes it,
> > > thanks.--b.
> >
> > By the way, config NFS_V4_2_READ_PLUS still says:
> >
> >         This is intended for developers only. The READ_PLUS operation
> >         has been shown to have issues under specific conditions and
> >         should not be used in production.
> >
> > But this warning was the only thing I was seeing.  Is there another
> > known issue remaining?
> 
> I think it was an issue around using lseek to generate the reply. The
> file contents could change between each call, leading to inconsistent
> results (and a new failing xfstest that previously passed)

OK, thanks, I see now that you mentioned in 21e31401fc45 "NFS: Disable
READ_PLUS by default" that there were generic/091 and generic/263
failures.

Looks like they're both testing concurrent direct and buffered IO.  I
don't know what we try to guarantee in that case.

--b.

> 
> Anna
> 
> >
> > --b.
> >
> > >
> > > > I found that we could end up accessing xdr->buf->pages[pgnr] with a pgnr
> > > > greater than the number of pages in the array. So let's just return
> > > > early if we're setting base to a point at the end of the page data and
> > > > let xdr_set_tail_base() handle setting up the buffer pointers instead.
> > > >
> > > > Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
> > > > ---
> > > >  net/sunrpc/xdr.c | 7 +++----
> > > >  1 file changed, 3 insertions(+), 4 deletions(-)
> > > >
> > > > diff --git a/net/sunrpc/xdr.c b/net/sunrpc/xdr.c
> > > > index 3964ff74ee51..ca10ba2626f2 100644
> > > > --- a/net/sunrpc/xdr.c
> > > > +++ b/net/sunrpc/xdr.c
> > > > @@ -1230,10 +1230,9 @@ static unsigned int xdr_set_page_base(struct xdr_stream *xdr,
> > > >     void *kaddr;
> > > >
> > > >     maxlen = xdr->buf->page_len;
> > > > -   if (base >= maxlen) {
> > > > -           base = maxlen;
> > > > -           maxlen = 0;
> > > > -   } else
> > > > +   if (base >= maxlen)
> > > > +           return 0;
> > > > +   else
> > > >             maxlen -= base;
> > > >     if (len > maxlen)
> > > >             len = maxlen;
> > > > --
> > > > 2.32.0

Re: [PATCH] sunrpc: Avoid a KASAN slab-out-of-bounds bug in xdr_set_page_base()

[J. Bruce Fields]

On Thu, Aug 26, 2021 at 04:42:21PM -0400, J. Bruce Fields wrote:
> On Thu, Aug 26, 2021 at 03:44:32PM -0400, Anna Schumaker wrote:
> > On Thu, Aug 12, 2021 at 4:32 PM J. Bruce Fields <bfields@fieldses.org> wrote:
> > >
> > > On Mon, Jun 14, 2021 at 07:14:40PM -0400, bfields wrote:
> > > > On Wed, Jun 09, 2021 at 05:07:29PM -0400, schumaker.anna@gmail.com wrote:
> > > > > From: Anna Schumaker <Anna.Schumaker@Netapp.com>
> > > > >
> > > > > This seems to happen fairly easily during READ_PLUS testing on NFS v4.2.
> > > >
> > > > Yep, I hit a KASAN warning here every time, and this fixes it,
> > > > thanks.--b.
> > >
> > > By the way, config NFS_V4_2_READ_PLUS still says:
> > >
> > >         This is intended for developers only. The READ_PLUS operation
> > >         has been shown to have issues under specific conditions and
> > >         should not be used in production.
> > >
> > > But this warning was the only thing I was seeing.  Is there another
> > > known issue remaining?
> > 
> > I think it was an issue around using lseek to generate the reply. The
> > file contents could change between each call, leading to inconsistent
> > results (and a new failing xfstest that previously passed)
> 
> OK, thanks, I see now that you mentioned in 21e31401fc45 "NFS: Disable
> READ_PLUS by default" that there were generic/091 and generic/263
> failures.
> 
> Looks like they're both testing concurrent direct and buffered IO.  I
> don't know what we try to guarantee in that case.

But I'd assumed generic/263 just wasn't supported on nfs anyway.--b.

generic/263 81s ... [failed, exit status 1]- output mismatch (see /root/xfstests-dev/results//generic/263.out.bad)
    --- tests/generic/263.out	2019-12-20 17:34:10.493343575 -0500
    +++ /root/xfstests-dev/results//generic/263.out.bad	2021-08-26 16:43:40.751891500 -0400
    @@ -1,3 +1,262 @@
     QA output created by 263
     fsx -N 10000 -o 8192 -l 500000 -r PSIZE -t BSIZE -w BSIZE -Z
     fsx -N 10000 -o 128000 -l 500000 -r PSIZE -t BSIZE -w BSIZE -Z
    +Seed set to 1
    +main: filesystem does not support fallocate mode FALLOC_FL_KEEP_SIZE, disabling!
    +main: filesystem does not support fallocate mode FALLOC_FL_ZERO_RANGE, disabling!
    +main: filesystem does not support fallocate mode FALLOC_FL_COLLAPSE_RANGE, disabling!
    ...
    (Run 'diff -u /root/xfstests-dev/tests/generic/263.out /root/xfstests-dev/results//generic/263.out.bad'  to see the entire diff)
Ran: generic/263
Failures: generic/263
Failed 1 of 1 tests