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Subject: Re: [PATCH v1] NFS: Fix rpcrdma_inline_fixup() crash with new LISTXATTRS
 operation
Date:   Tue, 1 Dec 2020 20:25:32 +0000
From:   Frank van der Linden <fllinden@amazon.com>
To:     Olga Kornievskaia <aglo@umich.edu>
CC:     Chuck Lever <chuck.lever@oracle.com>,
        "Kornievskaia, Olga" <Olga.Kornievskaia@netapp.com>,
        Linux NFS Mailing List <linux-nfs@vger.kernel.org>
Message-ID: <20201201202532.GA3723@dev-dsk-fllinden-2c-c1893d73.us-west-2.amazon.com>
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On Tue, Dec 01, 2020 at 03:01:57PM -0500, Olga Kornievskaia wrote:
> 
> 
> On Fri, Nov 27, 2020 at 3:40 AM Frank van der Linden
> <fllinden@amazon.com> wrote:
> >
> > On Thu, Nov 26, 2020 at 12:10:21PM -0500, Chuck Lever wrote:
> > >
> > >
> > > > On Nov 25, 2020, at 7:21 PM, Frank van der Linden <fllinden@amazon.com> wrote:
> > > >
> > > > On Tue, Nov 24, 2020 at 10:40:25PM +0000, Kornievskaia, Olga wrote:
> > > >>
> > > >>
> > > >> ﻿On 11/24/20, 4:20 PM, "Frank van der Linden" <fllinden@amazon.com> wrote:
> > > >>
> > > >>    On Tue, Nov 24, 2020 at 08:50:36PM +0000, Kornievskaia, Olga wrote:
> > > >>>
> > > >>>
> > > >>> On 11/24/20, 3:06 PM, "Frank van der Linden" <fllinden@amazon.com> wrote:
> > > >>>
> > > >>>    On Tue, Nov 24, 2020 at 12:26:32PM -0500, Chuck Lever wrote:
> > > >>>>
> > > >>>>
> > > >>>>
> > > >>>> By switching to an XFS-backed export, I am able to reproduce the
> > > >>>> ibcomp worker crash on my client with xfstests generic/013.
> > > >>>>
> > > >>>> For the failing LISTXATTRS operation, xdr_inline_pages() is called
> > > >>>> with page_len=12 and buflen=128. Then:
> > > >>>>
> > > >>>> - Because buflen is small, rpcrdma_marshal_req will not set up a
> > > >>>>  Reply chunk and the rpcrdma's XDRBUF_SPARSE_PAGES logic does not
> > > >>>>  get invoked at all.
> > > >>>>
> > > >>>> - Because page_len is non-zero, rpcrdma_inline_fixup() tries to
> > > >>>>  copy received data into rq_rcv_buf->pages, but they're missing.
> > > >>>>
> > > >>>> The result is that the ibcomp worker faults and dies. Sometimes that
> > > >>>> causes a visible crash, and sometimes it results in a transport
> > > >>>> hang without other symptoms.
> > > >>>>
> > > >>>> RPC/RDMA's XDRBUF_SPARSE_PAGES support is not entirely correct, and
> > > >>>> should eventually be fixed or replaced. However, my preference is
> > > >>>> that upper-layer operations should explicitly allocate their receive
> > > >>>> buffers (using GFP_KERNEL) when possible, rather than relying on
> > > >>>> XDRBUF_SPARSE_PAGES.
> > > >>>>
> > > >>>> Reported-by: Olga kornievskaia <kolga@netapp.com>
> > > >>>> Suggested-by: Olga kornievskaia <kolga@netapp.com>
> > > >>>> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
> > > >>>> ---
> > > >>>> fs/nfs/nfs42proc.c |   17 ++++++++++-------
> > > >>>> fs/nfs/nfs42xdr.c  |    1 -
> > > >>>> 2 files changed, 10 insertions(+), 8 deletions(-)
> > > >>>>
> > > >>>> Hi-
> > > >>>>
> > > >>>> I like Olga's proposed approach. What do you think of this patch?
> > > >>>>
> > > >>>>
> > > >>>> diff --git a/fs/nfs/nfs42proc.c b/fs/nfs/nfs42proc.c
> > > >>>> index 2b2211d1234e..24810305ec1c 100644
> > > >>>> --- a/fs/nfs/nfs42proc.c
> > > >>>> +++ b/fs/nfs/nfs42proc.c
> > > >>>> @@ -1241,7 +1241,7 @@ static ssize_t _nfs42_proc_listxattrs(struct inode *inode, void *buf,
> > > >>>>                .rpc_resp       = &res,
> > > >>>>        };
> > > >>>>        u32 xdrlen;
> > > >>>> -       int ret, np;
> > > >>>> +       int ret, np, i;
> > > >>>>
> > > >>>>
> > > >>>>        res.scratch = alloc_page(GFP_KERNEL);
> > > >>>> @@ -1253,10 +1253,14 @@ static ssize_t _nfs42_proc_listxattrs(struct inode *inode, void *buf,
> > > >>>>                xdrlen = server->lxasize;
> > > >>>>        np = xdrlen / PAGE_SIZE + 1;
> > > >>>>
> > > >>>> +       ret = -ENOMEM;
> > > >>>>        pages = kcalloc(np, sizeof(struct page *), GFP_KERNEL);
> > > >>>> -       if (pages == NULL) {
> > > >>>> -               __free_page(res.scratch);
> > > >>>> -               return -ENOMEM;
> > > >>>> +       if (pages == NULL)
> > > >>>> +               goto out_free;
> > > >>>> +       for (i = 0; i < np; i++) {
> > > >>>> +               pages[i] = alloc_page(GFP_KERNEL);
> > > >>>> +               if (!pages[i])
> > > >>>> +                       goto out_free;
> > > >>>>        }
> > > >>>>
> > > >>>>        arg.xattr_pages = pages;
> > > >>>> @@ -1271,14 +1275,13 @@ static ssize_t _nfs42_proc_listxattrs(struct inode *inode, void *buf,
> > > >>>>                *eofp = res.eof;
> > > >>>>        }
> > > >>>>
> > > >>>> +out_free:
> > > >>>>        while (--np >= 0) {
> > > >>>>                if (pages[np])
> > > >>>>                        __free_page(pages[np]);
> > > >>>>        }
> > > >>>> -
> > > >>>> -       __free_page(res.scratch);
> > > >>>>        kfree(pages);
> > > >>>> -
> > > >>>> +       __free_page(res.scratch);
> > > >>>>        return ret;
> > > >>>>
> > > >>>> }
> > > >>>> diff --git a/fs/nfs/nfs42xdr.c b/fs/nfs/nfs42xdr.c
> > > >>>> index 6e060a88f98c..8432bd6b95f0 100644
> > > >>>> --- a/fs/nfs/nfs42xdr.c
> > > >>>> +++ b/fs/nfs/nfs42xdr.c
> > > >>>> @@ -1528,7 +1528,6 @@ static void nfs4_xdr_enc_listxattrs(struct rpc_rqst *req,
> > > >>>>
> > > >>>>        rpc_prepare_reply_pages(req, args->xattr_pages, 0, args->count,
> > > >>>>            hdr.replen);
> > > >>>> -       req->rq_rcv_buf.flags |= XDRBUF_SPARSE_PAGES;
> > > >>>>
> > > >>>>        encode_nops(&hdr);
> > > >>>> }
> > > >>>>
> > > >>>>
> > > >>>
> > > >>>    I can see why this is the simplest and most pragmatic solution, so it's
> > > >>>    fine with me.
> > > >>>
> > > >>>    Why doesn't this happen with getxattr? Do we need to convert that too?
> > > >>>
> > > >>> [olga] I don't know if GETXATTR/SETXATTR works. I'm not sure what tests exercise those operations. I just ran into the fact that generic/013 wasn't passing. And I don't see that it's an xattr specific tests. I'm not sure how it ends up triggering is usage of xattr.
> > > >>
> > > >>    I'm attaching the test program I used, it should give things a better workout.
> > > >>
> > > >> [olga] I'm not sure if I'm doing something wrong but there are only 2 GETXATTR call on the network trace from running this application and both calls are returning an error (ERR_NOXATTR). Which btw might explain why no problems are seen since no decoding of data is happening. There are lots of SETXATTRs and REMOVEXATTR and there is a LISTXATTR (which btw network trace is marking as malformed so there might something bad there). Anyway...
> > > >>
> > > >> This is my initial report: no real exercise of the GETXATTR code as far as I can tell.
> > > >
> > > > True, the test is heavier on the setxattr / listxattr side. And with caching,
> > > > you're not going to see a lot of GETXATTR calls. I used the same test program
> > > > with caching off, and it works fine, though.
> > >
> > > I unintentionally broke GETXATTR while developing the LISTXATTRS fix,
> > > and generic/013 rather aggressively informed me that GETXATTR was no
> > > longer working. There is some test coverage there, fwiw.
> >
> > Oh, the coverage was good - in my testing I also used a collection of
> > small unit test programs, and I was the one who made the xattr tests
> > in xfstests work on NFS.
> 
> I have just oops-ed the kernel trying to send a getxattr when
> userspace provided a small buffer.
> 
> File with extended attributes was created using your application but
> modified to leave the file behind. Then I coded up this to get the
> extended attirbutes. Test coverage doesn't test for this.
> 
> int main(int argc, char *argv[]) {
> 
> int fd, len = 8;
> char buf[8];
> 
> fd = open("/mnt/test_xattr_probeJxfiVU", O_RDWR | O_CREAT, S_IRWXU);
> if (fd < 0) exit(0);
> 
> if (getxattr("/mnt/test_xattr_probeJxfiVU", "user.test_xattr_probe",
> buf, len) < 0) exit(0);
> 
> return 0;
> }
> 
> Which again produces the KASAN's
> [ 5915.393103] BUG: KASAN: wild-memory-access in
> rpcrdma_complete_rqst+0x41b/0x680 [rpcrdma]
> 
> 
> This is my proposed fix. Will send a proper patch if agreed:

I was just about to send a patch that does the pre-alloc, and rounds up
the inserted page_len to the page allocation so that it'll catch some
more replies to cache.

Let me send it..

- Frank