[PATCH net] net/sched: Fix memory leak in tcindex_set_parms

[PATCH net] net/sched: Fix memory leak in tcindex_set_parms

[Chen Zhongjin]

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@vger.kernel.org
Reported-by: syzbot+2f9183cb6f89b0e16586@syzkaller.appspotmail.com
Signed-off-by: Chen Zhongjin <chenzhongjin@huawei.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

Re: [PATCH net] net/sched: Fix memory leak in tcindex_set_parms

[Chen Zhongjin]

Hi,

On 2022/12/8 11:22, Chen Zhongjin wrote:
> 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@vger.kernel.org
> Reported-by: syzbot+2f9183cb6f89b0e16586@syzkaller.appspotmail.com
> Signed-off-by: Chen Zhongjin <chenzhongjin@huawei.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);

Just noticed that Hawkins has sent a patch for this. Please ignore mine.

Thanks!

Re: [syzbot] memory leak in tcindex_set_parms (3)

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-and-tested-by: syzbot+2f9183cb6f89b0e16586@syzkaller.appspotmail.com

Tested on:

commit:         355479c7 Merge tag 'efi-fixes-for-v6.1-4' of git://git..
git tree:       https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
console output: https://syzkaller.appspot.com/x/log.txt?x=175b5b23880000
kernel config:  https://syzkaller.appspot.com/x/.config?x=979161df0e247659
dashboard link: https://syzkaller.appspot.com/bug?extid=2f9183cb6f89b0e16586
compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
patch:          https://syzkaller.appspot.com/x/patch.diff?x=142313f3880000

Note: testing is done by a robot and is best-effort only.