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    Subject[PATCH 5.4 356/411] SUNRPC: Fix the calculation of xdr->end in xdr_get_next_encode_buffer()
    Date
    From: Chuck Lever <chuck.lever@oracle.com>

    [ Upstream commit 6c254bf3b637dd4ef4f78eb78c7447419c0161d7 ]

    I found that NFSD's new NFSv3 READDIRPLUS XDR encoder was screwing up
    right at the end of the page array. xdr_get_next_encode_buffer() does
    not compute the value of xdr->end correctly:

    * The check to see if we're on the final available page in xdr->buf
    needs to account for the space consumed by @nbytes.

    * The new xdr->end value needs to account for the portion of @nbytes
    that is to be encoded into the previous buffer.

    Fixes: 2825a7f90753 ("nfsd4: allow encoding across page boundaries")
    Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
    Reviewed-by: NeilBrown <neilb@suse.de>
    Reviewed-by: J. Bruce Fields <bfields@fieldses.org>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    net/sunrpc/xdr.c | 6 +++++-
    1 file changed, 5 insertions(+), 1 deletion(-)

    diff --git a/net/sunrpc/xdr.c b/net/sunrpc/xdr.c
    index 7ef37054071f..cb8740d15633 100644
    --- a/net/sunrpc/xdr.c
    +++ b/net/sunrpc/xdr.c
    @@ -608,7 +608,11 @@ static __be32 *xdr_get_next_encode_buffer(struct xdr_stream *xdr,
    */
    xdr->p = (void *)p + frag2bytes;
    space_left = xdr->buf->buflen - xdr->buf->len;
    - xdr->end = (void *)p + min_t(int, space_left, PAGE_SIZE);
    + if (space_left - nbytes >= PAGE_SIZE)
    + xdr->end = (void *)p + PAGE_SIZE;
    + else
    + xdr->end = (void *)p + space_left - frag1bytes;
    +
    xdr->buf->page_len += frag2bytes;
    xdr->buf->len += nbytes;
    return p;
    --
    2.35.1


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