Patch "bpf/verifier: fix min/max handling in BPF_SUB" has been added to the 4.12-stable tree

[<gregkh@linuxfoundation.org>]

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

    bpf/verifier: fix min/max handling in BPF_SUB

to the 4.12-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-verifier-fix-min-max-handling-in-bpf_sub.patch
and it can be found in the queue-4.12 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From foo@baz Thu Aug 24 17:43:45 PDT 2017
From: Edward Cree <ecree@solarflare.com>
Date: Fri, 21 Jul 2017 14:37:34 +0100
Subject: bpf/verifier: fix min/max handling in BPF_SUB

From: Edward Cree <ecree@solarflare.com>


[ Upstream commit 9305706c2e808ae59f1eb201867f82f1ddf6d7a6 ]

We have to subtract the src max from the dst min, and vice-versa, since
 (e.g.) the smallest result comes from the largest subtrahend.

Fixes: 484611357c19 ("bpf: allow access into map value arrays")
Signed-off-by: Edward Cree <ecree@solarflare.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 kernel/bpf/verifier.c |   21 +++++++++++++++------
 1 file changed, 15 insertions(+), 6 deletions(-)

--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -1858,10 +1858,12 @@ static void adjust_reg_min_max_vals(stru
 	 * do our normal operations to the register, we need to set the values
 	 * to the min/max since they are undefined.
 	 */
-	if (min_val == BPF_REGISTER_MIN_RANGE)
-		dst_reg->min_value = BPF_REGISTER_MIN_RANGE;
-	if (max_val == BPF_REGISTER_MAX_RANGE)
-		dst_reg->max_value = BPF_REGISTER_MAX_RANGE;
+	if (opcode != BPF_SUB) {
+		if (min_val == BPF_REGISTER_MIN_RANGE)
+			dst_reg->min_value = BPF_REGISTER_MIN_RANGE;
+		if (max_val == BPF_REGISTER_MAX_RANGE)
+			dst_reg->max_value = BPF_REGISTER_MAX_RANGE;
+	}
 
 	switch (opcode) {
 	case BPF_ADD:
@@ -1872,10 +1874,17 @@ static void adjust_reg_min_max_vals(stru
 		dst_reg->min_align = min(src_align, dst_align);
 		break;
 	case BPF_SUB:
+		/* If one of our values was at the end of our ranges, then the
+		 * _opposite_ value in the dst_reg goes to the end of our range.
+		 */
+		if (min_val == BPF_REGISTER_MIN_RANGE)
+			dst_reg->max_value = BPF_REGISTER_MAX_RANGE;
+		if (max_val == BPF_REGISTER_MAX_RANGE)
+			dst_reg->min_value = BPF_REGISTER_MIN_RANGE;
 		if (dst_reg->min_value != BPF_REGISTER_MIN_RANGE)
-			dst_reg->min_value -= min_val;
+			dst_reg->min_value -= max_val;
 		if (dst_reg->max_value != BPF_REGISTER_MAX_RANGE)
-			dst_reg->max_value -= max_val;
+			dst_reg->max_value -= min_val;
 		dst_reg->min_align = min(src_align, dst_align);
 		break;
 	case BPF_MUL:


Patches currently in stable-queue which might be from ecree@solarflare.com are

queue-4.12/bpf-fix-mixed-signed-unsigned-derived-min-max-value-bounds.patch
queue-4.12/bpf-verifier-fix-min-max-handling-in-bpf_sub.patch