The bpf_prog used in sock_setfilter() only attempts to check for
ip pktlen, and verifies that the contents of the 80'th packet in
the ethernet frame is 'a' or 'b'. Thus many non-udp packets
could incorrectly pass through this filter and cause incorrect
test results.
This commit hardens the conditions checked by the filter so
that only UDP/IPv4 packets with the matching length and test-character
will be permitted by the filter. The filter has been cleaned up
to explicitly use the BPF macros to make it more readable.
Signed-off-by: Sowmini Varadhan <sowmini.varadhan@xxxxxxxxxx>
Acked-by: Willem de Bruijn <willemb@xxxxxxxxxx>
---
v2: commit comment edited based on review
tools/testing/selftests/net/psock_lib.h | 28 +++++++++++++++++++++-------
1 files changed, 21 insertions(+), 7 deletions(-)
diff --git a/tools/testing/selftests/net/psock_lib.h b/tools/testing/selftests/net/psock_lib.h
index 24bc7ec..e62540e 100644
--- a/tools/testing/selftests/net/psock_lib.h
+++ b/tools/testing/selftests/net/psock_lib.h
@@ -27,6 +27,7 @@
#include <string.h>
#include <arpa/inet.h>
#include <unistd.h>
+#include <netinet/udp.h>
#define DATA_LEN 100
#define DATA_CHAR 'a'
@@ -40,14 +41,27 @@
static __maybe_unused void sock_setfilter(int fd, int lvl, int optnum)
{
+ uint16_t ip_len = DATA_LEN +
+ sizeof(struct iphdr) + sizeof(struct udphdr);
+ /* the filter below checks for all of the following conditions that
+ * are based on the contents of create_payload()
+ * ether type 0x800 and
+ * ip proto udp and
+ * ip len == ip_len and
+ * udp[38] == 'a' or udp[38] == 'b'
+ */
struct sock_filter bpf_filter[] = {
- { 0x80, 0, 0, 0x00000000 }, /* LD pktlen */
- { 0x35, 0, 4, DATA_LEN }, /* JGE DATA_LEN [f goto nomatch]*/
- { 0x30, 0, 0, 0x00000050 }, /* LD ip[80] */
- { 0x15, 1, 0, DATA_CHAR }, /* JEQ DATA_CHAR [t goto match]*/
- { 0x15, 0, 1, DATA_CHAR_1}, /* JEQ DATA_CHAR_1 [t goto match]*/
- { 0x06, 0, 0, 0x00000060 }, /* RET match */
- { 0x06, 0, 0, 0x00000000 }, /* RET no match */
+ BPF_STMT(BPF_LD | BPF_H | BPF_ABS, 12), /* LD ethertype */
+ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, ETH_P_IP, 0, 8),
+ BPF_STMT(BPF_LD|BPF_B|BPF_ABS, 23), /* LD ip_proto */
+ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, IPPROTO_UDP, 0, 6),
+ BPF_STMT(BPF_LD|BPF_H|BPF_ABS, 16), /* LD ip_len */
+ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, ip_len, 0, 4),
+ BPF_STMT(BPF_LD|BPF_B|BPF_ABS, 80), /* LD udp[38] */
+ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, DATA_CHAR, 1, 0),
+ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, DATA_CHAR_1, 0, 1),
+ BPF_STMT(BPF_RET | BPF_K, ~0), /* match */
+ BPF_STMT(BPF_RET | BPF_K, 0) /* no match */
};
struct sock_fprog bpf_prog;
--
1.7.1
--
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