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s390/qeth: reject oversized SNMP requests

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Commit d4c08afafa ("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: d4c08afafa ("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>
This commit is contained in:
Julian Wiedmann 2019-08-23 11:29:23 +02:00 committed by David S. Miller
parent b45ce32135
commit 292a50e3fc
1 changed files with 4 additions and 0 deletions
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4
drivers/s390/net/qeth_core_main.c
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@ -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;