FAILED: patch "[PATCH] net/sched: serialize qdisc_rtab_list against concurrent" failed to apply to 5.10-stable tree

PATCH New [email protected] 2 participants 2 messages Jul 29 – Aug 8

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[email protected]

author maintainer

2026-07-29 13:52 UTC #0 lore raw

The patch below does not apply to the 5.10-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.10.y
git checkout FETCH_HEAD
git cherry-pick -x f43ee0c0730d6191629b5ee1ceae27b1ebfdc047
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026072927-exploit-isotope-4690@gregkh' --subject-prefix 'PATCH 5.10.y' 'HEAD^..'

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From f43ee0c0730d6191629b5ee1ceae27b1ebfdc047 Mon Sep 17 00:00:00 2001
From: Aldo Ariel Panzardo <[email protected]>
Date: Wed, 15 Jul 2026 08:41:14 -0300
Subject: [PATCH] net/sched: serialize qdisc_rtab_list against concurrent
get/put

qdisc_get_rtab() and qdisc_put_rtab() mutate the process-global singly linked list qdisc_rtab_list and a plain non-atomic 'int refcnt' with no lock. This was only safe because every caller historically held the RTNL mutex, which serialized all rate-table lookups, inserts and frees.

That invariant no longer holds. cls_flower sets TCF_PROTO_OPS_DOIT_UNLOCKED, so tc_new_tfilter() keeps rtnl_held == false for it and sets TCA_ACT_FLAGS_NO_RTNL. That flag propagates through tcf_exts_validate_ex() -> tcf_action_init() -> tcf_action_init_1() -> tcf_police_init(), which calls qdisc_get_rtab()/qdisc_put_rtab() with the RTNL mutex NOT held. Two RTM_NEWTFILTER requests on different CPUs, each adding a flower filter with a police action carrying the same rate, then race on qdisc_rtab_list and on the non-atomic refcnt, leading to a use-after-free / double-free of the kmalloc-2k struct qdisc_rate_table. qdisc_rtab_list is a single global (not per-netns), so the corrupted object is shared system-wide.

  BUG: KASAN: slab-use-after-free in qdisc_put_rtab+0x12f/0x160
   qdisc_put_rtab+0x12f/0x160
   tcf_police_init+0xda9/0x1590
   tcf_action_init_1+0x460/0x6b0
   tcf_action_init+0x439/0xa40
   tcf_exts_validate_ex+0x42d/0x550
   fl_change+0xddd/0x7da0
   tc_new_tfilter+0xaa7/0x2420
   rtnetlink_rcv_msg+0x95e/0xe90
  which belongs to the cache kmalloc-2k of size 2048

Protect qdisc_rtab_list and the refcount with a dedicated spinlock. The (sleeping, GFP_KERNEL) allocation in qdisc_get_rtab() is performed before taking the lock; if a concurrent inserter added an identical table in the meantime the freshly allocated one is freed under the lock, so no duplicate is leaked. qdisc_put_rtab() now decrements the refcount and unlinks under the same lock.

Fixes 470502de5bdb ("net: sched: unlock rules update API")

Signed-off-by Aldo Ariel Panzardo <[email protected]>

Cc [email protected]

Acked-by Jamal Hadi Salim <[email protected]>

Reviewed-by Eric Dumazet <[email protected]>

Link https://patch.msgid.link/[email protected] open here

Signed-off-by Jakub Kicinski <[email protected]>

net/sched/sch_api.c +19 -5

index 8a3236456db4..668bcd60d183 100644
@@ -415,12 +415,13 @@ static __u8 __detect_linklayer(struct tc_ratespec *r, __u32 *rtab)
 }
 
 static struct qdisc_rate_table *qdisc_rtab_list;
+static DEFINE_SPINLOCK(qdisc_rtab_lock);
 
 struct qdisc_rate_table *qdisc_get_rtab(struct tc_ratespec *r,
 					struct nlattr *tab,
 					struct netlink_ext_ack *extack)
 {
-	struct qdisc_rate_table *rtab;
+	struct qdisc_rate_table *rtab, *new_rtab;
 
 	if (tab == NULL || r->rate == 0 ||
 	    r->cell_log == 0 || r->cell_log >= 32 ||

@@ -429,15 +430,20 @@ struct qdisc_rate_table *qdisc_get_rtab(struct tc_ratespec *r,
 		return NULL;
 	}
 
+	new_rtab = kmalloc_obj(*new_rtab);
+
+	spin_lock(&qdisc_rtab_lock);
 	for (rtab = qdisc_rtab_list; rtab; rtab = rtab->next) {
 		if (!memcmp(&rtab->rate, r, sizeof(struct tc_ratespec)) &&
 		    !memcmp(&rtab->data, nla_data(tab), TC_RTAB_SIZE)) {
 			rtab->refcnt++;
+			spin_unlock(&qdisc_rtab_lock);
+			kfree(new_rtab);
 			return rtab;
 		}
 	}
 
-	rtab = kmalloc_obj(*rtab);
+	rtab = new_rtab;
 	if (rtab) {
 		rtab->rate = *r;
 		rtab->refcnt = 1;

@@ -449,6 +455,7 @@ struct qdisc_rate_table *qdisc_get_rtab(struct tc_ratespec *r,
 	} else {
 		NL_SET_ERR_MSG(extack, "Failed to allocate new qdisc rate table");
 	}
+	spin_unlock(&qdisc_rtab_lock);
 	return rtab;
 }
 EXPORT_SYMBOL(qdisc_get_rtab);

@@ -457,18 +464,25 @@ void qdisc_put_rtab(struct qdisc_rate_table *tab)
 {
 	struct qdisc_rate_table *rtab, **rtabp;
 
-	if (!tab || --tab->refcnt)
+	if (!tab)
 		return;
 
+	spin_lock(&qdisc_rtab_lock);
+	if (--tab->refcnt) {
+		spin_unlock(&qdisc_rtab_lock);
+		return;
+	}
+
 	for (rtabp = &qdisc_rtab_list;
 	     (rtab = *rtabp) != NULL;
 	     rtabp = &rtab->next) {
 		if (rtab == tab) {
 			*rtabp = rtab->next;
-			kfree(rtab);
-			return;
+			break;
 		}
 	}
+	spin_unlock(&qdisc_rtab_lock);
+	kfree(tab);
 }
 EXPORT_SYMBOL(qdisc_put_rtab);

Sasha Levin

maintainer

2026-08-08 16:47 UTC #1 lore raw

PATCH 1/1 net/sched: serialize qdisc_rtab_list against concurrent get/put

From: Aldo Ariel Panzardo <[email protected]>

[ Upstream commit f43ee0c0730d6191629b5ee1ceae27b1ebfdc047 ]

  BUG: KASAN: slab-use-after-free in qdisc_put_rtab+0x12f/0x160
   qdisc_put_rtab+0x12f/0x160
   tcf_police_init+0xda9/0x1590
   tcf_action_init_1+0x460/0x6b0
   tcf_action_init+0x439/0xa40
   tcf_exts_validate_ex+0x42d/0x550
   fl_change+0xddd/0x7da0
   tc_new_tfilter+0xaa7/0x2420
   rtnetlink_rcv_msg+0x95e/0xe90
  which belongs to the cache kmalloc-2k of size 2048