Patch "bpf: improve verifier packet range checks" has been added to the 4.10-stable tree

PATCH [email protected] 1 participant 1 message Apr 29, 2017

Subsystems (5)

Stable branch Kselftest BPF BPF selftests +1 more subsystems

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2017-04-29 06:23 UTC #0 lore raw

This is a note to let you know that I've just added the patch titled

bpf: improve verifier packet range checks

to the 4.10-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
bpf-improve-verifier-packet-range-checks.patch
and it can be found in the queue-4.10 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

Quoted 1 line

From foo@baz Sat Apr 29 08:22:40 CEST 2017

From: Alexei Starovoitov <[email protected]>
Date: Fri, 24 Mar 2017 15:57:33 -0700
Subject: bpf: improve verifier packet range checks

From: Alexei Starovoitov <[email protected]>

[ Upstream commit b1977682a3858b5584ffea7cfb7bd863f68db18d ]

llvm can optimize the 'if (ptr > data_end)' checks to be in the order slightly different than the original C code which will confuse verifier. Like:
if (ptr + 16 > data_end)
return TC_ACT_SHOT;
// may be followed by
if (ptr + 14 > data_end)
return TC_ACT_SHOT;
while llvm can see that 'ptr' is valid for all 16 bytes,
the verifier could not.
Fix verifier logic to account for such case and add a test.

Reported-by Huapeng Zhou <[email protected]>

Fixes 969bf05eb3ce ("bpf: direct packet access")

Signed-off-by Alexei Starovoitov <[email protected]>

Acked-by Daniel Borkmann <[email protected]>

Acked-by Martin KaFai Lau <[email protected]>

Signed-off-by David S. Miller <[email protected]>

Signed-off-by Greg Kroah-Hartman <[email protected]>

---
 kernel/bpf/verifier.c                       |    5 +++--
 tools/testing/selftests/bpf/test_verifier.c |   20 ++++++++++++++++++++
 2 files changed, 23 insertions(+), 2 deletions(-)

kernel/bpf/verifier.c +3 -2

@@ -1859,14 +1859,15 @@ static void find_good_pkt_pointers(struc
 
 	for (i = 0; i < MAX_BPF_REG; i++)
 		if (regs[i].type == PTR_TO_PACKET && regs[i].id == dst_reg->id)
-			regs[i].range = dst_reg->off;
+			/* keep the maximum range already checked */
+			regs[i].range = max(regs[i].range, dst_reg->off);
 
 	for (i = 0; i < MAX_BPF_STACK; i += BPF_REG_SIZE) {
 		if (state->stack_slot_type[i] != STACK_SPILL)
 			continue;
 		reg = &state->spilled_regs[i / BPF_REG_SIZE];
 		if (reg->type == PTR_TO_PACKET && reg->id == dst_reg->id)
-			reg->range = dst_reg->off;
+			reg->range = max(reg->range, dst_reg->off);
 	}
 }

tools/testing/selftests/bpf/test_verifier.c +20 -0

@@ -2876,6 +2876,26 @@ static struct bpf_test tests[] = {
 		.prog_type = BPF_PROG_TYPE_LWT_XMIT,
 	},
 	{
+		"overlapping checks for direct packet access",
+		.insns = {
+			BPF_LDX_MEM(BPF_W, BPF_REG_2, BPF_REG_1,
+				    offsetof(struct __sk_buff, data)),
+			BPF_LDX_MEM(BPF_W, BPF_REG_3, BPF_REG_1,
+				    offsetof(struct __sk_buff, data_end)),
+			BPF_MOV64_REG(BPF_REG_0, BPF_REG_2),
+			BPF_ALU64_IMM(BPF_ADD, BPF_REG_0, 8),
+			BPF_JMP_REG(BPF_JGT, BPF_REG_0, BPF_REG_3, 4),
+			BPF_MOV64_REG(BPF_REG_1, BPF_REG_2),
+			BPF_ALU64_IMM(BPF_ADD, BPF_REG_1, 6),
+			BPF_JMP_REG(BPF_JGT, BPF_REG_1, BPF_REG_3, 1),
+			BPF_LDX_MEM(BPF_H, BPF_REG_0, BPF_REG_2, 6),
+			BPF_MOV64_IMM(BPF_REG_0, 0),
+			BPF_EXIT_INSN(),
+		},
+		.result = ACCEPT,
+		.prog_type = BPF_PROG_TYPE_LWT_XMIT,
+	},
+	{
 		"invalid access of tc_classid for LWT_IN",
 		.insns = {
 			BPF_LDX_MEM(BPF_W, BPF_REG_0, BPF_REG_1,

Patches currently in stable-queue which might be from [email protected] are

queue-4.10/bpf-improve-verifier-packet-range-checks.patch