tree b970a0f3c2ae8a967116f534d454c58d2dff4d6e
parent 92d438857c7a972c3c27fe28f233b3077bd0e316
author Pedro Tammela <pctammela@mojatatu.com> 1729788947 -0400
committer COS Cherry Picker <cloud-image-release@prod.google.com> 1731061977 -0800

net/sched: stop qdisc_tree_reduce_backlog on TC_H_ROOT

[ Upstream commit 2e95c4384438adeaa772caa560244b1a2efef816 ]

In qdisc_tree_reduce_backlog, Qdiscs with major handle ffff: are assumed
to be either root or ingress. This assumption is bogus since it's valid
to create egress qdiscs with major handle ffff:
Budimir Markovic found that for qdiscs like DRR that maintain an active
class list, it will cause a UAF with a dangling class pointer.

In 066a3b5b2346, the concern was to avoid iterating over the ingress
qdisc since its parent is itself. The proper fix is to stop when parent
TC_H_ROOT is reached because the only way to retrieve ingress is when a
hierarchy which does not contain a ffff: major handle call into
qdisc_lookup with TC_H_MAJ(TC_H_ROOT).

In the scenario where major ffff: is an egress qdisc in any of the tree
levels, the updates will also propagate to TC_H_ROOT, which then the
iteration must stop.

Fixes: 066a3b5b2346 ("[NET_SCHED] sch_api: fix qdisc_tree_decrease_qlen() loop")
Reported-by: Budimir Markovic <markovicbudimir@gmail.com>
Suggested-by: Jamal Hadi Salim <jhs@mojatatu.com>
Tested-by: Victor Nogueira <victor@mojatatu.com>
Signed-off-by: Pedro Tammela <pctammela@mojatatu.com>
Signed-off-by: Jamal Hadi Salim <jhs@mojatatu.com>

 net/sched/sch_api.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
Reviewed-by: Simon Horman <horms@kernel.org>

BUG=b/377213048
TEST=presubmit
RELEASE_NOTE=Fixed KCTF-2e95c43 in the Linux kernel.

cos-patch: security-high
Link: https://patch.msgid.link/20241024165547.418570-1-jhs@mojatatu.com
Change-Id: Ied6348261e0fd510e47443b6ab9ae32827aa0dbd
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Reviewed-on: https://cos-review.googlesource.com/c/third_party/kernel/+/85561
Main-Branch-Verified: Cusky Presubmit Bot <presubmit@cos-infra-prod.iam.gserviceaccount.com>
Tested-by: Cusky Presubmit Bot <presubmit@cos-infra-prod.iam.gserviceaccount.com>
Reviewed-by: Oleksandr Tymoshenko <ovt@google.com>