Patch "mpls, nospec: Sanitize array index in mpls_label_ok()" has been added to the 4.15-stable tree

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

mpls, nospec: Sanitize array index in mpls_label_ok()

to the 4.15-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:
mpls-nospec-sanitize-array-index-in-mpls_label_ok.patch
and it can be found in the queue-4.15 subdirectory.

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

From: Dan Williams <[email protected]>
Date: Wed, 7 Feb 2018 22:34:24 -0800
Subject: mpls, nospec: Sanitize array index in mpls_label_ok()

From: Dan Williams <[email protected]>

commit 3968523f855050b8195134da951b87c20bd66130 upstream.

mpls_label_ok() validates that the 'platform_label' array index from a userspace netlink message payload is valid. Under speculation the mpls_label_ok() result may not resolve in the CPU pipeline until after the index is used to access an array element. Sanitize the index to zero to prevent userspace-controlled arbitrary out-of-bounds speculation, a precursor for a speculative execution side channel vulnerability.

---
 net/mpls/af_mpls.c |   24 ++++++++++++++----------
 1 file changed, 14 insertions(+), 10 deletions(-)

@@ -8,6 +8,7 @@
 #include <linux/ipv6.h>
 #include <linux/mpls.h>
 #include <linux/netconf.h>
+#include <linux/nospec.h>
 #include <linux/vmalloc.h>
 #include <linux/percpu.h>
 #include <net/ip.h>

@@ -935,24 +936,27 @@ errout:
 	return err;
 }
 
-static bool mpls_label_ok(struct net *net, unsigned int index,
+static bool mpls_label_ok(struct net *net, unsigned int *index,
 			  struct netlink_ext_ack *extack)
 {
+	bool is_ok = true;
+
 	/* Reserved labels may not be set */
-	if (index < MPLS_LABEL_FIRST_UNRESERVED) {
+	if (*index < MPLS_LABEL_FIRST_UNRESERVED) {
 		NL_SET_ERR_MSG(extack,
 			       "Invalid label - must be MPLS_LABEL_FIRST_UNRESERVED or higher");
-		return false;
+		is_ok = false;
 	}
 
 	/* The full 20 bit range may not be supported. */
-	if (index >= net->mpls.platform_labels) {
+	if (is_ok && *index >= net->mpls.platform_labels) {
 		NL_SET_ERR_MSG(extack,
 			       "Label >= configured maximum in platform_labels");
-		return false;
+		is_ok = false;
 	}
 
-	return true;
+	*index = array_index_nospec(*index, net->mpls.platform_labels);
+	return is_ok;
 }
 
 static int mpls_route_add(struct mpls_route_config *cfg,

@@ -975,7 +979,7 @@ static int mpls_route_add(struct mpls_ro
 		index = find_free_label(net);
 	}
 
-	if (!mpls_label_ok(net, index, extack))
+	if (!mpls_label_ok(net, &index, extack))
 		goto errout;
 
 	/* Append makes no sense with mpls */

@@ -1052,7 +1056,7 @@ static int mpls_route_del(struct mpls_ro
 
 	index = cfg->rc_label;
 
-	if (!mpls_label_ok(net, index, extack))
+	if (!mpls_label_ok(net, &index, extack))
 		goto errout;
 
 	mpls_route_update(net, index, NULL, &cfg->rc_nlinfo);

@@ -1810,7 +1814,7 @@ static int rtm_to_route_config(struct sk
 				goto errout;
 
 			if (!mpls_label_ok(cfg->rc_nlinfo.nl_net,
-					   cfg->rc_label, extack))
+					   &cfg->rc_label, extack))
 				goto errout;
 			break;
 		}

@@ -2137,7 +2141,7 @@ static int mpls_getroute(struct sk_buff
 			goto errout;
 		}
 
-		if (!mpls_label_ok(net, in_label, extack)) {
+		if (!mpls_label_ok(net, &in_label, extack)) {
 			err = -EINVAL;
 			goto errout;
 		}

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

queue-4.15/x86-entry-64-interleave-xor-register-clearing-with-push-instructions.patch queue-4.15/nospec-move-array_index_nospec-parameter-checking-into-separate-macro.patch queue-4.15/x86-entry-64-merge-the-pop_c_regs-and-pop_extra_regs-macros-into-a-single-pop_regs-macro.patch queue-4.15/kvm-nvmx-set-the-cpu_based_use_msr_bitmaps-if-we-have-a-valid-l02-msr-bitmap.patch queue-4.15/x86-nvmx-properly-set-spec_ctrl-and-pred_cmd-before-merging-msrs.patch queue-4.15/x86-speculation-add-asm-msr-index.h-dependency.patch queue-4.15/mm-fix-memory-size-alignment-in-devm_memremap_pages_release.patch queue-4.15/x86-entry-64-use-push_and_clean_regs-in-more-cases.patch queue-4.15/x86-speculation-update-speculation-control-microcode-blacklist.patch queue-4.15/x86-entry-64-clear-registers-for-exceptions-interrupts-to-reduce-speculation-attack-surface.patch queue-4.15/x86-speculation-correct-speculation-control-microcode-blacklist-again.patch queue-4.15/x86-entry-64-merge-save_c_regs-and-save_extra_regs-remove-unused-extensions.patch queue-4.15/x86-entry-64-indent-push_and_clear_regs-and-pop_regs-properly.patch queue-4.15/x86-speculation-fix-up-array_index_nospec_mask-asm-constraint.patch queue-4.15/x86-entry-64-clear-extra-registers-beyond-syscall-arguments-to-reduce-speculation-attack-surface.patch queue-4.15/kvm-x86-reduce-retpoline-performance-impact-in-slot_handle_level_range-by-always-inlining-iterator-helper-methods.patch queue-4.15/x86-mm-pti-fix-pti-comment-in-entry_syscall_64.patch queue-4.15/x86-entry-64-get-rid-of-the-alloc_pt_gpregs_on_stack-and-save_and_clear_regs-macros.patch queue-4.15/mpls-nospec-sanitize-array-index-in-mpls_label_ok.patch queue-4.15/x86-speculation-clean-up-various-spectre-related-details.patch queue-4.15/x86-entry-64-introduce-the-push_and_clean_regs-macro.patch queue-4.15/revert-x86-speculation-simplify-indirect_branch_prediction_barrier.patch queue-4.15/x86-entry-64-compat-clear-registers-for-compat-syscalls-to-reduce-speculation-attack-surface.patch queue-4.15/x86-entry-64-fix-cr3-restore-in-paranoid_exit.patch