From 35dc6e27ae11a92553611a9d3d8c1ed963a894d4 Mon Sep 17 00:00:00 2001 From: Ludovico Cavedon Date: Tue, 9 Jan 2018 10:26:10 -0800 Subject: Fix MPLS header parsing in ndpiReader. Reported at https://bugs.debian.org/886133. The current parsing for the MPLS header in examples/ndpi_util.c has multiple issues: - the bitfield order is incorrect for little endian architectures - ntohl() is applied to a 20 bit label, which has unclear purpose - if multiple labels are detected, the while loop parsing labels will never exit due to a missing re-read of the mpls label - the last label is identified by looking inside the label field, while it should be done by looking at the S bit This change fixes the above issues. Notice that bitfield ordering is implementation-dependent, so C bitfields should not be used in the first place to parse network packets. --- example/ndpi_util.c | 15 +++++++++------ src/include/ndpi_typedefs.h | 8 ++++++++ 2 files changed, 17 insertions(+), 6 deletions(-) diff --git a/example/ndpi_util.c b/example/ndpi_util.c index d0a8470dc..af83c6d14 100644 --- a/example/ndpi_util.c +++ b/example/ndpi_util.c @@ -689,7 +689,10 @@ struct ndpi_proto ndpi_workflow_process_packet (struct ndpi_workflow * workflow, const struct ndpi_wifi_header *wifi; /* --- MPLS header --- */ - struct ndpi_mpls_header *mpls; + union mpls { + uint32_t u32; + struct ndpi_mpls_header mpls; + } mpls; /** --- IP header --- **/ struct ndpi_iphdr *iph; @@ -846,15 +849,15 @@ struct ndpi_proto ndpi_workflow_process_packet (struct ndpi_workflow * workflow, break; case MPLS_UNI: case MPLS_MULTI: - mpls = (struct ndpi_mpls_header *) &packet[ip_offset]; - label = ntohl(mpls->label); - /* label = ntohl(*((u_int32_t*)&packet[ip_offset])); */ + mpls.u32 = *((uint32_t *) &packet[ip_offset]); + mpls.u32 = ntohl(mpls.u32); workflow->stats.mpls_count++; type = ETH_P_IP, ip_offset += 4; - while((label & 0x100) != 0x100) { + while(!mpls.mpls.s) { ip_offset += 4; - label = ntohl(mpls->label); + mpls.u32 = *((uint32_t *) &packet[ip_offset]); + mpls.u32 = ntohl(mpls.u32); } break; case PPPoE: diff --git a/src/include/ndpi_typedefs.h b/src/include/ndpi_typedefs.h index beb6a86f8..d0afcb40c 100644 --- a/src/include/ndpi_typedefs.h +++ b/src/include/ndpi_typedefs.h @@ -178,7 +178,15 @@ struct ndpi_wifi_header PACK_ON struct ndpi_mpls_header { + /* Before using this strcut to parse an MPLS header, you will need to convert + * the 4-byte data to the correct endianess with ntohl(). */ +#if defined(__LITTLE_ENDIAN__) + u_int32_t ttl:8, s:1, exp:3, label:20; +#elif defined(__BIG_ENDIAN__) u_int32_t label:20, exp:3, s:1, ttl:8; +#else +# error "Byte order must be defined" +#endif } PACK_OFF; /* ++++++++++++++++++++++++ IP header ++++++++++++++++++++++++ */ -- cgit v1.2.3