Messages in this thread Patch in this message | | | Date | Tue, 18 Jul 2017 20:10:31 -0400 (EDT) | From | Shu Wang <> | Subject | Re: [PATCH] audit: fix memleak in auditd_send_unicast_skb. |
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----- Original Message ----- > From: "Paul Moore" <paul@paul-moore.com> > To: shuwang@redhat.com > Cc: "Eric Paris" <eparis@redhat.com>, linux-audit@redhat.com, linux-kernel@vger.kernel.org, liwang@redhat.com, > chuhu@redhat.com > Sent: Tuesday, July 18, 2017 8:21:05 PM > Subject: Re: [PATCH] audit: fix memleak in auditd_send_unicast_skb. > > On Tue, Jul 18, 2017 at 2:37 AM, <shuwang@redhat.com> wrote: > > From: Shu Wang <shuwang@redhat.com> > > > > Found this issue by kmemleak report, auditd_send_unicast_skb > > did not free skb if rcu_dereference(auditd_conn) returns null. > > > > unreferenced object 0xffff88082568ce00 (size 256): > > comm "auditd", pid 1119, jiffies 4294708499 > > backtrace: > > [<ffffffff8176166a>] kmemleak_alloc+0x4a/0xa0 > > [<ffffffff8121820c>] kmem_cache_alloc_node+0xcc/0x210 > > [<ffffffff8161b99d>] __alloc_skb+0x5d/0x290 > > [<ffffffff8113c614>] audit_make_reply+0x54/0xd0 > > [<ffffffff8113dfa7>] audit_receive_msg+0x967/0xd70 > > ---------------- > > (gdb) list *audit_receive_msg+0x967 > > 0xffffffff8113dff7 is in audit_receive_msg (kernel/audit.c:1133). > > 1132 skb = audit_make_reply(0, AUDIT_REPLACE, 0, > > 0, &pvnr, sizeof(pvnr)); > > --------------- > > [<ffffffff8113e402>] audit_receive+0x52/0xa0 > > [<ffffffff8166c561>] netlink_unicast+0x181/0x240 > > [<ffffffff8166c8e2>] netlink_sendmsg+0x2c2/0x3b0 > > [<ffffffff816112e8>] sock_sendmsg+0x38/0x50 > > [<ffffffff816117a2>] SYSC_sendto+0x102/0x190 > > [<ffffffff81612f4e>] SyS_sendto+0xe/0x10 > > [<ffffffff8176d337>] entry_SYSCALL_64_fastpath+0x1a/0xa5 > > [<ffffffffffffffff>] 0xffffffffffffffff > > > > Signed-off-by: Shu Wang <shuwang@redhat.com> > > --- > > kernel/audit.c | 1 + > > 1 file changed, 1 insertion(+) > > Hello and thank you for the problem report, it is appreciated. This > was also reported by Masami Ichikawa who provided a patch with the > correct fix (your patch does not catch any error conditions from > netlink_unicast()).
netlink_unicast has it's error handling, and is responsible for releasing skb. so the Masami Ichikawa's fix may cause double free problems.
1274 int netlink_unicast(struct sock *ssk, struct sk_buff *skb, 1275 >--->--- u32 portid, int nonblock) 1276 { ...... 1285 >---sk = netlink_getsockbyportid(ssk, portid); 1286 >---if (IS_ERR(sk)) { 1287 >--->---kfree_skb(skb); 1288 >--->---return PTR_ERR(sk); 1289 >---} ...... 1293 >---if (sk_filter(sk, skb)) { 1294 >--->---err = skb->len; 1295 >--->---kfree_skb(skb); 1296 >--->---sock_put(sk); 1297 >--->---return err; 1298 >---}
> > * https://www.redhat.com/archives/linux-audit/2017-July/msg00073.html > > > diff --git a/kernel/audit.c b/kernel/audit.c > > index 833267b..6dd5569 100644 > > --- a/kernel/audit.c > > +++ b/kernel/audit.c > > @@ -641,6 +641,7 @@ static int auditd_send_unicast_skb(struct sk_buff *skb) > > ac = rcu_dereference(auditd_conn); > > if (!ac) { > > rcu_read_unlock(); > > + kfree_skb(skb); > > rc = -ECONNREFUSED; > > goto err; > > } > > -- > > 2.5.0 > > -- > paul moore > www.paul-moore.com >
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