Patch "bpf: improve verifier packet range checks" has been added to the 4.9-stable tree

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

bpf: improve verifier packet range checks

to the 4.9-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-4.9 subdirectory.

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

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.

---
 kernel/bpf/verifier.c |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

@@ -1829,14 +1829,15 @@ 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);
 	}
 }
 

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

queue-4.9/bpf-improve-verifier-packet-range-checks.patch