[NET]: Fix function put_cmsg() which may cause usr application memory overflow

When used function put_cmsg() to copy kernel information to user
application memory, if the memory length given by user application is
not enough, by the bad length calculate of msg.msg_controllen,
put_cmsg() function may cause the msg.msg_controllen to be a large
value, such as 0xFFFFFFF0, so the following put_cmsg() can also write
data to usr application memory even usr has no valid memory to store
this. This may cause usr application memory overflow.

int put_cmsg(struct msghdr * msg, int level, int type, int len, void *data)
{
    struct cmsghdr __user *cm
        = (__force struct cmsghdr __user *)msg->msg_control;
    struct cmsghdr cmhdr;
    int cmlen = CMSG_LEN(len);
    ~~~~~~~~~~~~~~~~~~~~~
    int err;

    if (MSG_CMSG_COMPAT & msg->msg_flags)
        return put_cmsg_compat(msg, level, type, len, data);

    if (cm==NULL || msg->msg_controllen < sizeof(*cm)) {
        msg->msg_flags |= MSG_CTRUNC;
        return 0; /* XXX: return error? check spec. */
    }
    if (msg->msg_controllen < cmlen) {
    ~~~~~~~~~~~~~~~~~~~~~~~~
        msg->msg_flags |= MSG_CTRUNC;
        cmlen = msg->msg_controllen;
    }
    cmhdr.cmsg_level = level;
    cmhdr.cmsg_type = type;
    cmhdr.cmsg_len = cmlen;

    err = -EFAULT;
    if (copy_to_user(cm, &cmhdr, sizeof cmhdr))
        goto out;
    if (copy_to_user(CMSG_DATA(cm), data, cmlen - sizeof(struct cmsghdr)))
        goto out;
    cmlen = CMSG_SPACE(len);
~~~~~~~~~~~~~~~~~~~~~~~~~~~
    If MSG_CTRUNC flags is set, msg->msg_controllen is less than
CMSG_SPACE(len), "msg->msg_controllen -= cmlen" will cause unsinged int
type msg->msg_controllen to be a large value.
~~~~~~~~~~~~~~~~~~~~~~~~~~~
    msg->msg_control += cmlen;
    msg->msg_controllen -= cmlen;
    ~~~~~~~~~~~~~~~~~~~~~
    err = 0;
out:
    return err;
}

The same promble exists in put_cmsg_compat(). This patch can fix this
problem.

Signed-off-by: Wei Yongjun <yjwei@cn.fujitsu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/compat.c b/net/compat.c
index d74d82155d78e20cd008a289751bcaca70b27f7a..377e560ab5c98bb99cc5d83340082c926b2c39de 100644 (file)
--- a/net/compat.c
+++ b/net/compat.c
@@ -254,6 +254,8 @@ int put_cmsg_compat(struct msghdr *kmsg, int level, int type, int len, void *dat
        if (copy_to_user(CMSG_COMPAT_DATA(cm), data, cmlen - sizeof(struct compat_cmsghdr)))
                return -EFAULT;
        cmlen = CMSG_COMPAT_SPACE(len);
+       if (kmsg->msg_controllen < cmlen)
+               cmlen = kmsg->msg_controllen;
        kmsg->msg_control += cmlen;
        kmsg->msg_controllen -= cmlen;
        return 0;

diff --git a/net/core/scm.c b/net/core/scm.c
index 100ba6d9d478d7df1082a3790ddfac0e6c012d73..10f5c65f6a470cc914de500b43d63990e89db1b6 100644 (file)
--- a/net/core/scm.c
+++ b/net/core/scm.c
@@ -196,6 +196,8 @@ int put_cmsg(struct msghdr * msg, int level, int type, int len, void *data)
        if (copy_to_user(CMSG_DATA(cm), data, cmlen - sizeof(struct cmsghdr)))
                goto out;
        cmlen = CMSG_SPACE(len);
+       if (msg->msg_controllen < cmlen)
+               cmlen = msg->msg_controllen;
        msg->msg_control += cmlen;
        msg->msg_controllen -= cmlen;
        err = 0;