From 1f415a74b0ca64b5bfacbb12d71ed2ec050a8cfb Mon Sep 17 00:00:00 2001 From: Jakub Kicinski Date: Tue, 2 Aug 2016 16:12:14 +0100 Subject: [PATCH] bpf: fix method of PTR_TO_PACKET reg id generation Using per-register incrementing ID can lead to find_good_pkt_pointers() confusing registers which have completely different values. Consider example: 0: (bf) r6 = r1 1: (61) r8 = *(u32 *)(r6 +76) 2: (61) r0 = *(u32 *)(r6 +80) 3: (bf) r7 = r8 4: (07) r8 += 32 5: (2d) if r8 > r0 goto pc+9 R0=pkt_end R1=ctx R6=ctx R7=pkt(id=0,off=0,r=32) R8=pkt(id=0,off=32,r=32) R10=fp 6: (bf) r8 = r7 7: (bf) r9 = r7 8: (71) r1 = *(u8 *)(r7 +0) 9: (0f) r8 += r1 10: (71) r1 = *(u8 *)(r7 +1) 11: (0f) r9 += r1 12: (07) r8 += 32 13: (2d) if r8 > r0 goto pc+1 R0=pkt_end R1=inv56 R6=ctx R7=pkt(id=0,off=0,r=32) R8=pkt(id=1,off=32,r=32) R9=pkt(id=1,off=0,r=32) R10=fp 14: (71) r1 = *(u8 *)(r9 +16) 15: (b7) r7 = 0 16: (bf) r0 = r7 17: (95) exit We need to get a UNKNOWN_VALUE with imm to force id generation so lines 0-5 make r7 a valid packet pointer. We then read two different bytes from the packet and add them to copies of the constructed packet pointer. r8 (line 9) and r9 (line 11) will get the same id of 1, independently. When either of them is validated (line 13) - find_good_pkt_pointers() will also mark the other as safe. This leads to access on line 14 being mistakenly considered safe. Fixes: 969bf05eb3ce ("bpf: direct packet access") Signed-off-by: Jakub Kicinski Acked-by: Alexei Starovoitov Acked-by: Daniel Borkmann Signed-off-by: David S. Miller --- kernel/bpf/verifier.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index f72f23b8fdab..7094c69ac199 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -194,6 +194,7 @@ struct verifier_env { struct verifier_state_list **explored_states; /* search pruning optimization */ struct bpf_map *used_maps[MAX_USED_MAPS]; /* array of map's used by eBPF program */ u32 used_map_cnt; /* number of used maps */ + u32 id_gen; /* used to generate unique reg IDs */ bool allow_ptr_leaks; }; @@ -1301,7 +1302,7 @@ static int check_packet_ptr_add(struct verifier_env *env, struct bpf_insn *insn) /* dst_reg stays as pkt_ptr type and since some positive * integer value was added to the pointer, increment its 'id' */ - dst_reg->id++; + dst_reg->id = ++env->id_gen; /* something was added to pkt_ptr, set range and off to zero */ dst_reg->off = 0;