Do not subtract the SLL[2]_HDR_LEN if the location is negative.

This fixes the offset issue I mention in the-tcpdump-group/tcpdump#480 (comment)
fenner · Apr 27, 2019 · 926dacf · 926dacf
1 parent 3e21907
commit 926dacf
Showing 1 changed file with 2 additions and 2 deletions.
diff --git a/pcap-linux.c b/pcap-linux.c
@@ -7427,7 +7427,7 @@ fix_offset(pcap_t *handle, struct bpf_insn *p)
 		/*
 		 * What's the offset?
 		 */
-		if (p->k >= SLL2_HDR_LEN) {
+		if ((bpf_int32)p->k >= SLL2_HDR_LEN) {
 			/*
 			 * It's within the link-layer payload; that starts
 			 * at an offset of 0, as far as the kernel packet
@@ -7459,7 +7459,7 @@ fix_offset(pcap_t *handle, struct bpf_insn *p)
 		/*
 		 * What's the offset?
 		 */
-		if (p->k >= SLL_HDR_LEN) {
+		if ((bpf_int32)p->k >= SLL_HDR_LEN) {
 			/*
 			 * It's within the link-layer payload; that starts
 			 * at an offset of 0, as far as the kernel packet