s390/qeth: reject oversized SNMP requests

Commit d4c08afafa04 ("s390/qeth: streamline SNMP cmd code") removed
the bounds checking for req_len, under the assumption that the check in
qeth_alloc_cmd() would suffice.

But that code path isn't sufficiently robust to handle a user-provided
data_length, which could overflow (when adding the cmd header overhead)
before being checked against QETH_BUFSIZE. We end up allocating just a
tiny iob, and the subsequent copy_from_user() writes past the end of
that iob.

Special-case this path and add a coarse bounds check, to protect against
maliciuous requests. This let's the subsequent code flow do its normal
job and precise checking, without risk of overflow.

Fixes: d4c08afafa04 ("s390/qeth: streamline SNMP cmd code")
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Julian Wiedmann <jwi@linux.ibm.com>
Reviewed-by: Ursula Braun <ubraun@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/drivers/s390/net/qeth_core_main.c b/drivers/s390/net/qeth_core_main.c
index 9c3310c..6502b14 100644 (file)
--- a/drivers/s390/net/qeth_core_main.c
+++ b/drivers/s390/net/qeth_core_main.c
@@ -4374,6 +4374,10 @@ static int qeth_snmp_command(struct qeth_card *card, char __user *udata)
            get_user(req_len, &ureq->hdr.req_len))
                return -EFAULT;
 
+       /* Sanitize user input, to avoid overflows in iob size calculation: */
+       if (req_len > QETH_BUFSIZE)
+               return -EINVAL;
+
        iob = qeth_get_adapter_cmd(card, IPA_SETADP_SET_SNMP_CONTROL, req_len);
        if (!iob)
                return -ENOMEM;