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sunrpc: correct the computation for page_ptr when truncating 

When truncating the encode buffer, the page_ptr is getting
advanced, causing the next page to be skipped while encoding.
The page is still included in the response, so the response
contains a page of bogus data.

We need to adjust the page_ptr backwards to ensure we encode
the next page into the correct place.

We saw this triggered when concurrent directory modifications caused
nfsd4_encode_direct_fattr() to return nfserr_noent, and the resulting
call to xdr_truncate_encode() corrupted the READDIR reply.

Signed-off-by: Frank Sorenson <sorenson@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
This commit is contained in:
Frank Sorenson 2018-10-30 15:10:40 -05:00 committed by J. Bruce Fields
parent 651022382c
commit 5d7a5bcb67
1 changed files with 2 additions and 3 deletions
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5
net/sunrpc/xdr.c
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@ -673,11 +673,10 @@ void xdr_truncate_encode(struct xdr_stream *xdr, size_t len)
WARN_ON_ONCE(xdr->iov); WARN_ON_ONCE(xdr->iov);
return; return;
} }
if (fraglen) { if (fraglen)
xdr->end = head->iov_base + head->iov_len; xdr->end = head->iov_base + head->iov_len;
xdr->page_ptr--;
}
/* (otherwise assume xdr->end is already set) */ /* (otherwise assume xdr->end is already set) */
xdr->page_ptr--;
head->iov_len = len; head->iov_len = len;
buf->len = len; buf->len = len;
xdr->p = head->iov_base + head->iov_len; xdr->p = head->iov_base + head->iov_len;