On Thu, 3 Jun 2021 15:32:03 -0700 Cong Wang xiyou.wangcong@gmail.com wrote:
On Wed, Jun 2, 2021 at 12:29 PM Pavel Skripkin paskripkin@gmail.com wrote:
Syzbot reported memory leak in kcm_sendmsg()[1]. The problem was in non-freed frag_list in case of error.
In the while loop:
if (head == skb) skb_shinfo(head)->frag_list = tskb; else skb->next = tskb;frag_list filled with skbs, but nothing was freeing them.
What do you mean by "nothing was freeing them"?
I am sure kfree_skb() will free those in frag_list:
654 static void skb_release_data(struct sk_buff *skb) 655 { 656 struct skb_shared_info *shinfo = skb_shinfo(skb); 657 int i; ... 669 if (shinfo->frag_list) 670 kfree_skb_list(shinfo->frag_list);
Indeed. I didn't know about that. Im sorry.
backtrace: [<0000000094c02615>] __alloc_skb+0x5e/0x250 net/core/skbuff.c:198 [<00000000e5386cbd>] alloc_skb include/linux/skbuff.h:1083 [inline] [<00000000e5386cbd>] kcm_sendmsg+0x3b6/0xa50 net/kcm/kcmsock.c:967 [1] [<00000000f1613a8a>] sock_sendmsg_nosec net/socket.c:652 [inline] [<00000000f1613a8a>] sock_sendmsg+0x4c/0x60 net/socket.c:672
Reported-and-tested-by: syzbot+b039f5699bd82e1fb011@syzkaller.appspotmail.com Fixes: ab7ac4eb9832 ("kcm: Kernel Connection Multiplexor module") Cc: stable@vger.kernel.org Signed-off-by: Pavel Skripkin paskripkin@gmail.com --- net/kcm/kcmsock.c | 5 +++++ 1 file changed, 5 insertions(+)
diff --git a/net/kcm/kcmsock.c b/net/kcm/kcmsock.c index 6201965bd822..1c572c8daced 100644 --- a/net/kcm/kcmsock.c +++ b/net/kcm/kcmsock.c @@ -1066,6 +1066,11 @@ static int kcm_sendmsg(struct socket *sock, struct msghdr *msg, size_t len) goto partial_message; }
if (skb_has_frag_list(head)) {kfree_skb_list(skb_shinfo(head)->frag_list);skb_shinfo(head)->frag_list = NULL;}if (head != kcm->seq_skb) kfree_skb(head);This exact kfree_skb() should free those in frag_list. If the above if condition does not meet for some reason, then fix that condition?
Thanks.
I will debug this today later. I think, this commit should be reverted, because it's broken. Or I can send next patch on top of this. What do you think of that, David?
With regards, Pavel Skripkin