From 744a4cf63e528c29840f45811d6fb93fd129b87d Mon Sep 17 00:00:00 2001 From: Jiri Pirko Date: Tue, 22 Aug 2017 22:46:49 +0200 Subject: [PATCH] net: sched: fix use after free when tcf_chain_destroy is called multiple times The goto_chain termination action takes a reference of a chain. In that case, there is an issue when block_put is called tcf_chain_destroy directly. The follo-up call of tcf_chain_put by goto_chain action free works with memory that is already freed. This was caught by kasan: [ 220.337908] BUG: KASAN: use-after-free in tcf_chain_put+0x1b/0x50 [ 220.344103] Read of size 4 at addr ffff88036d1f2cec by task systemd-journal/261 [ 220.353047] CPU: 0 PID: 261 Comm: systemd-journal Not tainted 4.13.0-rc5jiri+ #54 [ 220.360661] Hardware name: Mellanox Technologies Ltd. Mellanox switch/Mellanox x86 mezzanine board, BIOS 4.6.5 08/02/2016 [ 220.371784] Call Trace: [ 220.374290] [ 220.376355] dump_stack+0xd5/0x150 [ 220.391485] print_address_description+0x86/0x410 [ 220.396308] kasan_report+0x181/0x4c0 [ 220.415211] tcf_chain_put+0x1b/0x50 [ 220.418949] free_tcf+0x95/0xc0 So allow tcf_chain_destroy to be called multiple times, free only in case the reference count drops to 0. Fixes: 5bc1701881e3 ("net: sched: introduce multichain support for filters") Signed-off-by: Jiri Pirko Signed-off-by: David S. Miller --- net/sched/cls_api.c | 12 ++++++++++-- 1 file changed, 10 insertions(+), 2 deletions(-) diff --git a/net/sched/cls_api.c b/net/sched/cls_api.c index 9fd44c221347..45cd34eee727 100644 --- a/net/sched/cls_api.c +++ b/net/sched/cls_api.c @@ -215,9 +215,17 @@ static void tcf_chain_flush(struct tcf_chain *chain) static void tcf_chain_destroy(struct tcf_chain *chain) { - list_del(&chain->list); + /* May be already removed from the list by the previous call. */ + if (!list_empty(&chain->list)) + list_del_init(&chain->list); + tcf_chain_flush(chain); - kfree(chain); + + /* There might still be a reference held when we got here from + * tcf_block_put. Wait for the user to drop reference before free. + */ + if (!chain->refcnt) + kfree(chain); } struct tcf_chain *tcf_chain_get(struct tcf_block *block, u32 chain_index,