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tools: psock_lib: harden socket filter used by psock tests

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The filter added by sock_setfilter is intended to only permit
packets matching the pattern set up by create_payload(), but
we only check the ip_len, and a single test-character in
the IP packet to ensure this condition.

Harden the filter by adding additional constraints so that we only
permit UDP/IPv4 packets that meet the ip_len and test-character
requirements. Include the bpf_asm src as a comment, in case this
needs to be enhanced in the future

Signed-off-by: Sowmini Varadhan <sowmini.varadhan@oracle.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Sowmini Varadhan 2017-01-12 05:10:11 -08:00 committed by David S. Miller
parent 79471b10d6
commit 4d7b9dc1f3
1 changed files with 32 additions and 7 deletions
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39
tools/testing/selftests/net/psock_lib.h
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@ -40,14 +40,39 @@
static __maybe_unused void sock_setfilter(int fd, int lvl, int optnum)
{
/* 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
* skb->len == DATA_LEN and
* udp[38] == 'a' or udp[38] == 'b'
* It can be generated from the following bpf_asm input:
* ldh [12]
* jne #0x800, drop ; ETH_P_IP
* ldb [23]
* jneq #17, drop ; IPPROTO_UDP
* ld len ; ld skb->len
* jlt #100, drop ; DATA_LEN
* ldb [80]
* jeq #97, pass ; DATA_CHAR
* jne #98, drop ; DATA_CHAR_1
* pass:
* ret #-1
* drop:
* ret #0
*/
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 */
{ 0x28, 0, 0, 0x0000000c },
{ 0x15, 0, 8, 0x00000800 },
{ 0x30, 0, 0, 0x00000017 },
{ 0x15, 0, 6, 0x00000011 },
{ 0x80, 0, 0, 0000000000 },
{ 0x35, 0, 4, 0x00000064 },
{ 0x30, 0, 0, 0x00000050 },
{ 0x15, 1, 0, 0x00000061 },
{ 0x15, 0, 1, 0x00000062 },
{ 0x06, 0, 0, 0xffffffff },
{ 0x06, 0, 0, 0000000000 },
};
struct sock_fprog bpf_prog;