[PATCH 7.1 013/228] s390/qeth: validate user buffer length in SNMP and ARP query ioctls

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

------------------

From: Hidayath Khan <[email protected]>

commit d141f087b1af656f055d7c5793a3e87817ba0bbe upstream.

qeth_snmp_command() and qeth_l3_arp_query() allocate a buffer sized by
a user-supplied length (udata_len) without checking a lower bound, then
set udata_offset to a fixed non-zero value and pass both to a reply
callback. The callback bounds-checks the copy with

        if ((udata_len - udata_offset) < len)

Both fields are u32, so a udata_len smaller than udata_offset makes the
subtraction wrap and the check pass, and the following memcpy() writes
past the allocation. A udata_len of 0 also yields ZERO_SIZE_PTR from
kzalloc(), which the existing NULL check does not catch.

Reject buffers smaller than udata_offset before allocating, so the
callback subtraction can no longer underflow.

Fixes: 4a71df50047f ("qeth: new qeth device driver")
Cc: [email protected]
Reviewed-by: Alexandra Winter <[email protected]>
Signed-off-by: Hidayath Khan <[email protected]>
Reviewed-by: Joe Damato <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
 drivers/s390/net/qeth_core_main.c |    3 +++
 drivers/s390/net/qeth_l3_main.c   |    5 +++++
 2 files changed, 8 insertions(+)

--- a/drivers/s390/net/qeth_core_main.c
+++ b/drivers/s390/net/qeth_core_main.c
@@ -4710,6 +4710,9 @@ static int qeth_snmp_command(struct qeth
 	if (req_len > QETH_BUFSIZE)
 		return -EINVAL;
 
+	if (qinfo.udata_len < sizeof(struct qeth_snmp_ureq_hdr))
+		return -EINVAL;
+
 	iob = qeth_get_adapter_cmd(card, IPA_SETADP_SET_SNMP_CONTROL, req_len);
 	if (!iob)
 		return -ENOMEM;
--- a/drivers/s390/net/qeth_l3_main.c
+++ b/drivers/s390/net/qeth_l3_main.c
@@ -1415,6 +1415,11 @@ static int qeth_l3_arp_query(struct qeth
 		rc = -EFAULT;
 		goto out;
 	}
+
+	if (qinfo.udata_len < QETH_QARP_ENTRIES_OFFSET) {
+		rc = -EINVAL;
+		goto out;
+	}
 	qinfo.udata = kzalloc(qinfo.udata_len, GFP_KERNEL);
 	if (!qinfo.udata) {
 		rc = -ENOMEM;