| Message ID | 20201026104333.13008-1-tung.q.nguyen@dektech.com.au |
|---|---|
| State | New |
| Headers | show |
| Series | [tipc-discussion,net,v2,1/1] tipc: fix memory leak caused by tipc_buf_append() | expand |
On Mon, 26 Oct 2020 17:43:33 +0700 Tung Nguyen wrote: > Commit ed42989eab57 ("fix the skb_unshare() in tipc_buf_append()") > replaced skb_unshare() with skb_copy() to not reduce the data reference > counter of the original skb intentionally. This is not the correct > way to handle the cloned skb because it causes memory leak in 2 > following cases: > 1/ Sending multicast messages via broadcast link > The original skb list is cloned to the local skb list for local > destination. After that, the data reference counter of each skb > in the original list has the value of 2. This causes each skb not > to be freed after receiving ACK: > tipc_link_advance_transmq() > { > ... > /* release skb */ > __skb_unlink(skb, &l->transmq); > kfree_skb(skb); <-- memory exists after being freed > } > > 2/ Sending multicast messages via replicast link > Similar to the above case, each skb cannot be freed after purging > the skb list: > tipc_mcast_xmit() > { > ... > __skb_queue_purge(pkts); <-- memory exists after being freed > } > > This commit fixes this issue by using skb_unshare() instead. Besides, > to avoid use-after-free error reported by KASAN, the pointer to the > fragment is set to NULL before calling skb_unshare() to make sure that > the original skb is not freed after freeing the fragment 2 times in > case skb_unshare() returns NULL. > > Fixes: ed42989eab57 ("fix the skb_unshare() in tipc_buf_append()") > Acked-by: Jon Maloy <jmaloy@redhat.com> > Reported-by: Thang Hoang Ngo <thang.h.ngo@dektech.com.au> > Signed-off-by: Tung Nguyen <tung.q.nguyen@dektech.com.au> Fixes tag: Fixes: ed42989eab57 ("fix the skb_unshare() in tipc_buf_append()") Has these problem(s): - Subject does not match target commit subject Just use git log -1 --format='Fixes: %h ("%s")'
On Mon, Oct 26, 2020 at 3:46 AM Tung Nguyen <tung.q.nguyen@dektech.com.au> wrote: > > Commit ed42989eab57 ("fix the skb_unshare() in tipc_buf_append()") > replaced skb_unshare() with skb_copy() to not reduce the data reference > counter of the original skb intentionally. This is not the correct > way to handle the cloned skb because it causes memory leak in 2 > following cases: > 1/ Sending multicast messages via broadcast link > The original skb list is cloned to the local skb list for local > destination. After that, the data reference counter of each skb > in the original list has the value of 2. This causes each skb not > to be freed after receiving ACK: Interesting, I can not immediately see how tipc_link_advance_transmq() clones the skb. You point out how it is freed but not cloned. It looks really odd to see the skb is held by some caller, then expected to be released by the unshare in tipc_buf_append(). IMHO, the refcnt should be released where it is held. Can you be more specific here? Thanks.
On Tue, Oct 27, 2020 at 11:21 AM Cong Wang <xiyou.wangcong@gmail.com> wrote: > > On Mon, Oct 26, 2020 at 3:46 AM Tung Nguyen > <tung.q.nguyen@dektech.com.au> wrote: > > > > Commit ed42989eab57 ("fix the skb_unshare() in tipc_buf_append()") > > replaced skb_unshare() with skb_copy() to not reduce the data reference > > counter of the original skb intentionally. This is not the correct > > way to handle the cloned skb because it causes memory leak in 2 > > following cases: > > 1/ Sending multicast messages via broadcast link > > The original skb list is cloned to the local skb list for local > > destination. After that, the data reference counter of each skb > > in the original list has the value of 2. This causes each skb not > > to be freed after receiving ACK: > > Interesting, I can not immediately see how tipc_link_advance_transmq() > clones the skb. You point out how it is freed but not cloned. > > It looks really odd to see the skb is held by some caller, then expected > to be released by the unshare in tipc_buf_append(). IMHO, the refcnt > should be released where it is held. More importantly, prior to Xin Long's change of skb_unshare(), skb_unclone() was used, which does not touch the skb refcnt either. So, why does it rely on skb_unshare() to release this refcnt now? Thanks.
diff --git a/net/tipc/msg.c b/net/tipc/msg.c index 2a78aa701572..32c79c59052b 100644 --- a/net/tipc/msg.c +++ b/net/tipc/msg.c @@ -150,12 +150,11 @@ int tipc_buf_append(struct sk_buff **headbuf, struct sk_buff **buf) if (fragid == FIRST_FRAGMENT) { if (unlikely(head)) goto err; - if (skb_cloned(frag)) - frag = skb_copy(frag, GFP_ATOMIC); + *buf = NULL; + frag = skb_unshare(frag, GFP_ATOMIC); if (unlikely(!frag)) goto err; head = *headbuf = frag; - *buf = NULL; TIPC_SKB_CB(head)->tail = NULL; if (skb_is_nonlinear(head)) { skb_walk_frags(head, tail) {
Commit ed42989eab57 ("fix the skb_unshare() in tipc_buf_append()") replaced skb_unshare() with skb_copy() to not reduce the data reference counter of the original skb intentionally. This is not the correct way to handle the cloned skb because it causes memory leak in 2 following cases: 1/ Sending multicast messages via broadcast link The original skb list is cloned to the local skb list for local destination. After that, the data reference counter of each skb in the original list has the value of 2. This causes each skb not to be freed after receiving ACK: tipc_link_advance_transmq() { ... /* release skb */ __skb_unlink(skb, &l->transmq); kfree_skb(skb); <-- memory exists after being freed } 2/ Sending multicast messages via replicast link Similar to the above case, each skb cannot be freed after purging the skb list: tipc_mcast_xmit() { ... __skb_queue_purge(pkts); <-- memory exists after being freed } This commit fixes this issue by using skb_unshare() instead. Besides, to avoid use-after-free error reported by KASAN, the pointer to the fragment is set to NULL before calling skb_unshare() to make sure that the original skb is not freed after freeing the fragment 2 times in case skb_unshare() returns NULL. Fixes: ed42989eab57 ("fix the skb_unshare() in tipc_buf_append()") Acked-by: Jon Maloy <jmaloy@redhat.com> Reported-by: Thang Hoang Ngo <thang.h.ngo@dektech.com.au> Signed-off-by: Tung Nguyen <tung.q.nguyen@dektech.com.au> --- net/tipc/msg.c | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-)