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    Subject[PATCH AUTOSEL 5.5 009/542] nfsd4: avoid NULL deference on strange COPY compounds
    Date
    From: "J. Bruce Fields" <bfields@redhat.com>

    [ Upstream commit d781e3df710745fbbaee4eb07fd5b64331a1b175 ]

    With cross-server COPY we've introduced the possibility that the current
    or saved filehandle might not have fh_dentry/fh_export filled in, but we
    missed a place that assumed it was. I think this could be triggered by
    a compound like:

    PUTFH(foreign filehandle)
    GETATTR
    SAVEFH
    COPY

    First, check_if_stalefh_allowed sets no_verify on the first (PUTFH) op.
    Then op_func = nfsd4_putfh runs and leaves current_fh->fh_export NULL.
    need_wrongsec_check returns true, since this PUTFH has OP_IS_PUTFH_LIKE
    set and GETATTR does not have OP_HANDLES_WRONGSEC set.

    We should probably also consider tightening the checks in
    check_if_stalefh_allowed and double-checking that we don't assume the
    filehandle is verified elsewhere in the compound. But I think this
    fixes the immediate issue.

    Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
    Fixes: 4e48f1cccab3 "NFSD: allow inter server COPY to have... "
    Signed-off-by: J. Bruce Fields <bfields@redhat.com>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    fs/nfsd/nfs4proc.c | 3 ++-
    1 file changed, 2 insertions(+), 1 deletion(-)

    diff --git a/fs/nfsd/nfs4proc.c b/fs/nfsd/nfs4proc.c
    index 4798667af647c..4d1d0bf8e385f 100644
    --- a/fs/nfsd/nfs4proc.c
    +++ b/fs/nfsd/nfs4proc.c
    @@ -2025,7 +2025,8 @@ nfsd4_proc_compound(struct svc_rqst *rqstp)
    if (op->opdesc->op_flags & OP_CLEAR_STATEID)
    clear_current_stateid(cstate);

    - if (need_wrongsec_check(rqstp))
    + if (current_fh->fh_export &&
    + need_wrongsec_check(rqstp))
    op->status = check_nfsd_access(current_fh->fh_export, rqstp);
    }
    encode_op:
    --
    2.20.1
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