| Message ID | 20210125195927.GA26972@chinagar-linux.qualcomm.com (mailing list archive) |
|---|---|
| State | Superseded |
| Delegated to: | Netdev Maintainers |
| Headers | show |
| Series | neighbour: Prevent a dead entry from updating gc_list | expand |
On Mon, Jan 25, 2021 at 11:59 AM Chinmay Agarwal <chinagar@codeaurora.org> wrote: > > Following race condition was detected: > <CPU A, t0> - neigh_flush_dev() is under execution and calls neigh_mark_dead(n), > marking the neighbour entry 'n' as dead. > > <CPU B, t1> - Executing: __netif_receive_skb() -> __netif_receive_skb_core() > -> arp_rcv() -> arp_process().arp_process() calls __neigh_lookup() which takes > a reference on neighbour entry 'n'. > > <CPU A, t2> - Moves further along neigh_flush_dev() and calls > neigh_cleanup_and_release(n), but since reference count increased in t2, > 'n' couldn't be destroyed. > > <CPU B, t3> - Moves further along, arp_process() and calls > neigh_update()-> __neigh_update() -> neigh_update_gc_list(), which adds > the neighbour entry back in gc_list(neigh_mark_dead(), removed it > earlier in t0 from gc_list) > > <CPU B, t4> - arp_process() finally calls neigh_release(n), destroying > the neighbour entry. > > This leads to 'n' still being part of gc_list, but the actual > neighbour structure has been freed. > > The situation can be prevented from happening if we disallow a dead > entry to have any possibility of updating gc_list. This is what the > patch intends to achieve. > > Signed-off-by: Chinmay Agarwal <chinagar@codeaurora.org> Please add a Fixes tag for bug fixes, in this case it is probably: Fixes: 9c29a2f55ec0 ("neighbor: Fix locking order for gc_list changes") And, make sure you run checkpatch.pl before sending out. For your patch, it will definitely complain about the missing spaces around the assignment "new=old;". Thanks.
On Tue, 26 Jan 2021 01:29:37 +0530 Chinmay Agarwal wrote: > Following race condition was detected: > <CPU A, t0> - neigh_flush_dev() is under execution and calls neigh_mark_dead(n), > marking the neighbour entry 'n' as dead. > > <CPU B, t1> - Executing: __netif_receive_skb() -> __netif_receive_skb_core() > -> arp_rcv() -> arp_process().arp_process() calls __neigh_lookup() which takes > a reference on neighbour entry 'n'. > > <CPU A, t2> - Moves further along neigh_flush_dev() and calls > neigh_cleanup_and_release(n), but since reference count increased in t2, > 'n' couldn't be destroyed. > > <CPU B, t3> - Moves further along, arp_process() and calls > neigh_update()-> __neigh_update() -> neigh_update_gc_list(), which adds > the neighbour entry back in gc_list(neigh_mark_dead(), removed it > earlier in t0 from gc_list) > > <CPU B, t4> - arp_process() finally calls neigh_release(n), destroying > the neighbour entry. > > This leads to 'n' still being part of gc_list, but the actual > neighbour structure has been freed. > > The situation can be prevented from happening if we disallow a dead > entry to have any possibility of updating gc_list. This is what the > patch intends to achieve. > > Signed-off-by: Chinmay Agarwal <chinagar@codeaurora.org> > --- > net/core/neighbour.c | 7 ++++--- > 1 file changed, 4 insertions(+), 3 deletions(-) > > diff --git a/net/core/neighbour.c b/net/core/neighbour.c > index ff07358..cf8e3076 100644 > --- a/net/core/neighbour.c > +++ b/net/core/neighbour.c > @@ -1244,13 +1244,14 @@ static int __neigh_update(struct neighbour *neigh, const u8 *lladdr, > old = neigh->nud_state; > err = -EPERM; > > - if (!(flags & NEIGH_UPDATE_F_ADMIN) && > - (old & (NUD_NOARP | NUD_PERMANENT))) > - goto out; > if (neigh->dead) { > NL_SET_ERR_MSG(extack, "Neighbor entry is now dead"); > + new=old; > goto out; > } > + if (!(flags & NEIGH_UPDATE_F_ADMIN) && > + (old & (NUD_NOARP | NUD_PERMANENT))) > + goto out; > > ext_learn_change = neigh_update_ext_learned(neigh, flags, ¬ify); > Please run checkpatch on your patches: ERROR: spaces required around that '=' (ctx:VxV) #52: FILE: net/core/neighbour.c:1249: + new=old; ^
diff --git a/net/core/neighbour.c b/net/core/neighbour.c index ff07358..cf8e3076 100644 --- a/net/core/neighbour.c +++ b/net/core/neighbour.c @@ -1244,13 +1244,14 @@ static int __neigh_update(struct neighbour *neigh, const u8 *lladdr, old = neigh->nud_state; err = -EPERM; - if (!(flags & NEIGH_UPDATE_F_ADMIN) && - (old & (NUD_NOARP | NUD_PERMANENT))) - goto out; if (neigh->dead) { NL_SET_ERR_MSG(extack, "Neighbor entry is now dead"); + new=old; goto out; } + if (!(flags & NEIGH_UPDATE_F_ADMIN) && + (old & (NUD_NOARP | NUD_PERMANENT))) + goto out; ext_learn_change = neigh_update_ext_learned(neigh, flags, ¬ify);
Following race condition was detected: <CPU A, t0> - neigh_flush_dev() is under execution and calls neigh_mark_dead(n), marking the neighbour entry 'n' as dead. <CPU B, t1> - Executing: __netif_receive_skb() -> __netif_receive_skb_core() -> arp_rcv() -> arp_process().arp_process() calls __neigh_lookup() which takes a reference on neighbour entry 'n'. <CPU A, t2> - Moves further along neigh_flush_dev() and calls neigh_cleanup_and_release(n), but since reference count increased in t2, 'n' couldn't be destroyed. <CPU B, t3> - Moves further along, arp_process() and calls neigh_update()-> __neigh_update() -> neigh_update_gc_list(), which adds the neighbour entry back in gc_list(neigh_mark_dead(), removed it earlier in t0 from gc_list) <CPU B, t4> - arp_process() finally calls neigh_release(n), destroying the neighbour entry. This leads to 'n' still being part of gc_list, but the actual neighbour structure has been freed. The situation can be prevented from happening if we disallow a dead entry to have any possibility of updating gc_list. This is what the patch intends to achieve. Signed-off-by: Chinmay Agarwal <chinagar@codeaurora.org> --- net/core/neighbour.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) --