[ovs-dev] [PATCH] odp-util: Stop key parsing if already oversized.

[Ilya Maximets]

We don't need to continue parsing if already oversized.  This is not
very important, but fuzzer times out while parsing very long flow.

The check could be written as a single 'if' statement, but I found
my variant much more readable.

Reported-at: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=35519
Signed-off-by: Ilya Maximets <i.maximets at ovn.org>
---
 lib/odp-util.c |  9 +++++++++
 tests/odp.at   | 14 ++++++++++++++
 2 files changed, 23 insertions(+)

diff --git a/lib/odp-util.c b/lib/odp-util.c
index 04a183c7c..7729a9060 100644
--- a/lib/odp-util.c
+++ b/lib/odp-util.c
@@ -6077,6 +6077,15 @@ odp_flow_from_string(const char *s, const struct simap *port_names,
         }
 
         retval = parse_odp_key_mask_attr(&context, s, key, mask);
+
+        if (retval >= 0) {
+            if (nl_attr_oversized(key->size - NLA_HDRLEN)) {
+                retval = -E2BIG;
+            } else if (mask && nl_attr_oversized(mask->size - NLA_HDRLEN)) {
+                retval = -E2BIG;
+            }
+        }
+
         if (retval < 0) {
             if (errorp) {
                 *errorp = xasprintf("syntax error at %s", s);
diff --git a/tests/odp.at b/tests/odp.at
index dccafd9d3..07a5cfe39 100644
--- a/tests/odp.at
+++ b/tests/odp.at
@@ -449,6 +449,20 @@ odp_actions_from_string: error
 ])
 AT_CLEANUP
 
+AT_SETUP([OVS datapath keys parsing and formatting - keys too long])
+dnl Flow keys should fit into a single netlink message.
+dnl Empty encap() takes 4 bytes.  So, 16384 is too many, but 16383 still fits.
+dnl We're getting 'duplicate attribute' error since it's not a logically valid
+dnl sequence of keys.  'syntax error' indicates oversized list of keys.
+keys=$(printf 'encap(),%.0s' $(seq 16382))
+echo "${keys}encap()" > keys.txt
+echo "${keys}encap(),encap()" >> keys.txt
+AT_CHECK([ovstest test-odp parse-keys < keys.txt | sed 's/encap(),//g'], [0], [dnl
+odp_flow_key_to_flow: error (duplicate encap attribute in flow key; the flow key in error is: encap())
+odp_flow_from_string: error (syntax error at encap())
+])
+AT_CLEANUP
+
 AT_SETUP([OVS datapath keys parsing and formatting - 33 nested encap ])
 AT_DATA([odp-in.txt], [dnl
 encap(encap(encap(encap(encap(encap(encap(encap(encap(encap(encap(encap(encap(encap(encap(encap(encap(encap(encap(encap(encap(encap(encap(encap(encap(encap(encap(encap(encap(encap(encap(encap(encap()))))))))))))))))))))))))))))))))
-- 
2.26.3