From: zhuoliang zhang <[email protected]>
we found that the following race condition exists in
xfrm_alloc_userspi flow:
user thread state_hash_work thread
---- ----
xfrm_alloc_userspi()
__find_acq_core()
/*alloc new xfrm_state:x*/
xfrm_state_alloc()
/*schedule state_hash_work thread*/
xfrm_hash_grow_check() xfrm_hash_resize()
xfrm_alloc_spi /*hold lock*/
x->id.spi = htonl(spi) spin_lock_bh(&net->xfrm.xfrm_state_lock)
/*waiting lock release*/ xfrm_hash_transfer()
spin_lock_bh(&net->xfrm.xfrm_state_lock) /*add x into hlist:net->xfrm.state_byspi*/
hlist_add_head_rcu(&x->byspi)
spin_unlock_bh(&net->xfrm.xfrm_state_lock)
/*add x into hlist:net->xfrm.state_byspi 2 times*/
hlist_add_head_rcu(&x->byspi)
So the same xfrm_stame (x) is added into the same list_hash
(net->xfrm.state_byspi)2 times that makes the list_hash become
a inifite loop.
To fix the race,x->id.spi = htonl(spi) in the xfrm_alloc_spi()
is moved to the back of spin_lock_bh,sothat state_hash_work thread
no longer add x which id.spi is zero into the hash_list.
Signed-off-by: zhuoliang zhang <[email protected]>
---
net/xfrm/xfrm_state.c | 8 +++++---
1 file changed, 5 insertions(+), 3 deletions(-)
diff --git a/net/xfrm/xfrm_state.c b/net/xfrm/xfrm_state.c
index bbd4643d7e82..a77da7aae6fe 100644
--- a/net/xfrm/xfrm_state.c
+++ b/net/xfrm/xfrm_state.c
@@ -2004,6 +2004,7 @@ int xfrm_alloc_spi(struct xfrm_state *x, u32 low, u32 high)
int err = -ENOENT;
__be32 minspi = htonl(low);
__be32 maxspi = htonl(high);
+ __be32 newspi = 0;
u32 mark = x->mark.v & x->mark.m;
spin_lock_bh(&x->lock);
@@ -2022,21 +2023,22 @@ int xfrm_alloc_spi(struct xfrm_state *x, u32 low, u32 high)
xfrm_state_put(x0);
goto unlock;
}
- x->id.spi = minspi;
+ newspi = minspi;
} else {
u32 spi = 0;
for (h = 0; h < high-low+1; h++) {
spi = low + prandom_u32()%(high-low+1);
x0 = xfrm_state_lookup(net, mark, &x->id.daddr, htonl(spi), x->id.proto, x->props.family);
if (x0 == NULL) {
- x->id.spi = htonl(spi);
+ newspi = htonl(spi);
break;
}
xfrm_state_put(x0);
}
}
- if (x->id.spi) {
+ if (newspi) {
spin_lock_bh(&net->xfrm.xfrm_state_lock);
+ x->id.spi = newspi;
h = xfrm_spi_hash(net, &x->id.daddr, x->id.spi, x->id.proto, x->props.family);
hlist_add_head_rcu(&x->byspi, net->xfrm.state_byspi + h);
spin_unlock_bh(&net->xfrm.xfrm_state_lock);
--
2.18.0
On Tue, Oct 20, 2020 at 04:18:00PM +0800, Zhuoliang Zhang wrote:
> From: zhuoliang zhang <[email protected]>
>
> we found that the following race condition exists in
> xfrm_alloc_userspi flow:
>
> user thread state_hash_work thread
> ---- ----
> xfrm_alloc_userspi()
> __find_acq_core()
> /*alloc new xfrm_state:x*/
> xfrm_state_alloc()
> /*schedule state_hash_work thread*/
> xfrm_hash_grow_check() xfrm_hash_resize()
> xfrm_alloc_spi /*hold lock*/
> x->id.spi = htonl(spi) spin_lock_bh(&net->xfrm.xfrm_state_lock)
> /*waiting lock release*/ xfrm_hash_transfer()
> spin_lock_bh(&net->xfrm.xfrm_state_lock) /*add x into hlist:net->xfrm.state_byspi*/
> hlist_add_head_rcu(&x->byspi)
> spin_unlock_bh(&net->xfrm.xfrm_state_lock)
>
> /*add x into hlist:net->xfrm.state_byspi 2 times*/
> hlist_add_head_rcu(&x->byspi)
>
> So the same xfrm_stame (x) is added into the same list_hash
> (net->xfrm.state_byspi)2 times that makes the list_hash become
> a inifite loop.
Your explanation makes no sense. Prior to obtaining the spin lock
on the LHS, the state x hasn't been added to thte table yet. So
how can the RHS be transferring it?
Cheers,
--
Email: Herbert Xu <[email protected]>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
On Thu, Oct 22, 2020 at 01:53:15PM +0800, zhuoliang.zhang wrote:
>
> there are 2 related hash lists : net->xfrm.state_bydst and
> net->xfrm.state_byspi:
>
> 1. a new state x is alloced in xfrm_state_alloc() and added into the
> bydst hlist in __find_acq_core() on the LHS;
> 2. on the RHS, state_hash_work thread travels the old bydst and tranfers
> every xfrm_state (include x) to the new bydst hlist and new byspi hlist;
> 3. user thread on the LHS gets the lock and adds x to the new byspi
> hlist again.
Good catch. Please add a Fixes header. I think this was introduced
with the dynamic resizing in f034b5d4efdfe0fb9e2a1ce1d95fa7914f24de49.
Thanks,
--
Email: Herbert Xu <[email protected]>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt