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    Subject[PATCH 5.7 089/179] nfsd4: fix NULL dereference in nfsd/clients display code
    Date
    From: J. Bruce Fields <bfields@redhat.com>

    [ Upstream commit 9affa435817711861d774f5626c393c80f16d044 ]

    We hold the cl_lock here, and that's enough to keep stateid's from going
    away, but it's not enough to prevent the files they point to from going
    away. Take fi_lock and a reference and check for NULL, as we do in
    other code.

    Reported-by: NeilBrown <neilb@suse.de>
    Fixes: 78599c42ae3c ("nfsd4: add file to display list of client's opens")
    Reviewed-by: NeilBrown <neilb@suse.de>
    Signed-off-by: J. Bruce Fields <bfields@redhat.com>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    fs/nfsd/nfs4state.c | 20 +++++++++++++++++++-
    1 file changed, 19 insertions(+), 1 deletion(-)

    diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
    index bdfae3ba39539..0a201bb074b0e 100644
    --- a/fs/nfsd/nfs4state.c
    +++ b/fs/nfsd/nfs4state.c
    @@ -509,6 +509,17 @@ find_any_file(struct nfs4_file *f)
    return ret;
    }

    +static struct nfsd_file *find_deleg_file(struct nfs4_file *f)
    +{
    + struct nfsd_file *ret = NULL;
    +
    + spin_lock(&f->fi_lock);
    + if (f->fi_deleg_file)
    + ret = nfsd_file_get(f->fi_deleg_file);
    + spin_unlock(&f->fi_lock);
    + return ret;
    +}
    +
    static atomic_long_t num_delegations;
    unsigned long max_delegations;

    @@ -2436,6 +2447,8 @@ static int nfs4_show_open(struct seq_file *s, struct nfs4_stid *st)
    oo = ols->st_stateowner;
    nf = st->sc_file;
    file = find_any_file(nf);
    + if (!file)
    + return 0;

    seq_printf(s, "- 0x%16phN: { type: open, ", &st->sc_stateid);

    @@ -2469,6 +2482,8 @@ static int nfs4_show_lock(struct seq_file *s, struct nfs4_stid *st)
    oo = ols->st_stateowner;
    nf = st->sc_file;
    file = find_any_file(nf);
    + if (!file)
    + return 0;

    seq_printf(s, "- 0x%16phN: { type: lock, ", &st->sc_stateid);

    @@ -2497,7 +2512,9 @@ static int nfs4_show_deleg(struct seq_file *s, struct nfs4_stid *st)

    ds = delegstateid(st);
    nf = st->sc_file;
    - file = nf->fi_deleg_file;
    + file = find_deleg_file(nf);
    + if (!file)
    + return 0;

    seq_printf(s, "- 0x%16phN: { type: deleg, ", &st->sc_stateid);

    @@ -2509,6 +2526,7 @@ static int nfs4_show_deleg(struct seq_file *s, struct nfs4_stid *st)

    nfs4_show_superblock(s, file);
    seq_printf(s, " }\n");
    + nfsd_file_put(file);

    return 0;
    }
    --
    2.25.1


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