linux-kernel - [PATCH net] net/sched: Fix memory leak in tcindex_set

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Date:   Thu, 8 Dec 2022 11:22:16 +0800
From:   Chen Zhongjin <chenzhongjin@...wei.com>
To:     <syzbot+2f9183cb6f89b0e16586@...kaller.appspotmail.com>,
        <syzkaller-bugs@...glegroups.com>, <netdev@...r.kernel.org>,
        <stable@...r.kernel.org>, <linux-kernel@...r.kernel.org>
CC:     <chenzhongjin@...wei.com>, <jhs@...atatu.com>,
        <xiyou.wangcong@...il.com>, <jiri@...nulli.us>,
        <davem@...emloft.net>, <edumazet@...gle.com>, <kuba@...nel.org>,
        <pabeni@...hat.com>, <gregkh@...uxfoundation.org>
Subject: [PATCH net] net/sched: Fix memory leak in tcindex_set_parms

syzkaller reported a memleak:
https://syzkaller.appspot.com/bug?id=e061e6cd46417ee6566dc249d8f982c0b5977a52

unreferenced object 0xffff888107813900 (size 256):
  backtrace:
    kcalloc include/linux/slab.h:636 [inline]
    tcf_exts_init include/net/pkt_cls.h:250 [inline]
    tcindex_set_parms+0xa7/0xbe0 net/sched/cls_tcindex.c:342
    tcindex_change+0xdf/0x120 net/sched/cls_tcindex.c:553
    tc_new_tfilter+0x4f2/0x1100 net/sched/cls_api.c:2147
    ...

The reproduce calls tc_new_tfilter() continuously:

tc_new_tfilter()...
tcindex_set_parms()
  tcf_exts_init(&e, ...) // alloc e->actions
  tcf_exts_change(&r->exts, &e)

tc_new_tfilter()...
tcindex_set_parms()
  old_r = r // same as first r
  tcindex_filter_result_init(old_r, cp, net);
  // old_r is holding e->actions but here it calls memset(old_r, 0)
  // so the previous e->actions is leaked

So here tcf_exts_destroy() should be called to free old_r->exts.actions
before memset(old_r, 0) sets it to NULL.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Cc: stable@...r.kernel.org
Reported-by: syzbot+2f9183cb6f89b0e16586@...kaller.appspotmail.com
Signed-off-by: Chen Zhongjin <chenzhongjin@...wei.com>
---
#syz test https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git 355479c70a48
---
 net/sched/cls_tcindex.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/net/sched/cls_tcindex.c b/net/sched/cls_tcindex.c
index 1c9eeb98d826..00a6c04a4b42 100644
--- a/net/sched/cls_tcindex.c
+++ b/net/sched/cls_tcindex.c
@@ -479,6 +479,7 @@ tcindex_set_parms(struct net *net, struct tcf_proto *tp, unsigned long base,
 	}
 
 	if (old_r && old_r != r) {
+		tcf_exts_destroy(&old_r->exts);
 		err = tcindex_filter_result_init(old_r, cp, net);
 		if (err < 0) {
 			kfree(f);
-- 
2.17.1