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    Subject[PATCH 3.12 83/91] RDS: fix race condition when sending a message on unbound socket
    Date
    From: Quentin Casasnovas <quentin.casasnovas@oracle.com>

    3.12-stable review patch. If anyone has any objections, please let me know.

    ===============

    commit 8c7188b23474cca017b3ef354c4a58456f68303a upstream.

    Sasha's found a NULL pointer dereference in the RDS connection code when
    sending a message to an apparently unbound socket. The problem is caused
    by the code checking if the socket is bound in rds_sendmsg(), which checks
    the rs_bound_addr field without taking a lock on the socket. This opens a
    race where rs_bound_addr is temporarily set but where the transport is not
    in rds_bind(), leading to a NULL pointer dereference when trying to
    dereference 'trans' in __rds_conn_create().

    Vegard wrote a reproducer for this issue, so kindly ask him to share if
    you're interested.

    I cannot reproduce the NULL pointer dereference using Vegard's reproducer
    with this patch, whereas I could without.

    Complete earlier incomplete fix to CVE-2015-6937:

    74e98eb08588 ("RDS: verify the underlying transport exists before creating a connection")

    Cc: David S. Miller <davem@davemloft.net>

    Reviewed-by: Vegard Nossum <vegard.nossum@oracle.com>
    Reviewed-by: Sasha Levin <sasha.levin@oracle.com>
    Acked-by: Santosh Shilimkar <santosh.shilimkar@oracle.com>
    Signed-off-by: Quentin Casasnovas <quentin.casasnovas@oracle.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    Signed-off-by: Jiri Slaby <jslaby@suse.cz>
    ---
    net/rds/connection.c | 6 ------
    net/rds/send.c | 4 +++-
    2 files changed, 3 insertions(+), 7 deletions(-)

    diff --git a/net/rds/connection.c b/net/rds/connection.c
    index e88bf3976e54..642ad42c416b 100644
    --- a/net/rds/connection.c
    +++ b/net/rds/connection.c
    @@ -177,12 +177,6 @@ static struct rds_connection *__rds_conn_create(__be32 laddr, __be32 faddr,
    }
    }

    - if (trans == NULL) {
    - kmem_cache_free(rds_conn_slab, conn);
    - conn = ERR_PTR(-ENODEV);
    - goto out;
    - }
    -
    conn->c_trans = trans;

    ret = trans->conn_alloc(conn, gfp);
    diff --git a/net/rds/send.c b/net/rds/send.c
    index 88eace57dd6b..31c9fa464b11 100644
    --- a/net/rds/send.c
    +++ b/net/rds/send.c
    @@ -955,11 +955,13 @@ int rds_sendmsg(struct kiocb *iocb, struct socket *sock, struct msghdr *msg,
    release_sock(sk);
    }

    - /* racing with another thread binding seems ok here */
    + lock_sock(sk);
    if (daddr == 0 || rs->rs_bound_addr == 0) {
    + release_sock(sk);
    ret = -ENOTCONN; /* XXX not a great errno */
    goto out;
    }
    + release_sock(sk);

    /* size of rm including all sgs */
    ret = rds_rm_size(msg, payload_len);
    --
    2.6.4


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