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Old 11-22-2011, 08:46 AM
Stefan Bader
 
Default ACK: inetpeer: reduce stack usage

On 21.11.2011 13:14, Andy Whitcroft wrote:
> From: Eric Dumazet <eric.dumazet@gmail.com>
>
> [ Upstream commit 66944e1c5797562cebe2d1857d46dff60bf9a69e ]
>
> On 64bit arches, we use 752 bytes of stack when cleanup_once() is called
> from inet_getpeer().
>
> Lets share the avl stack to save ~376 bytes.
>
> Before patch :
>
> 0x000006c3 unlink_from_pool [inetpeer.o]: 376
> 0x00000721 unlink_from_pool [inetpeer.o]: 376
> 0x00000cb1 inet_getpeer [inetpeer.o]: 376
> 0x00000e6d inet_getpeer [inetpeer.o]: 376
> 0x0004 inet_initpeers [inetpeer.o]: 112
> text data bss dec hex filename
> 5320 432 21 5773 168d net/ipv4/inetpeer.o
>
> After patch :
>
> objdump -d net/ipv4/inetpeer.o | scripts/checkstack.pl
> 0x00000c11 inet_getpeer [inetpeer.o]: 376
> 0x00000dcd inet_getpeer [inetpeer.o]: 376
> 0x00000ab9 peer_check_expire [inetpeer.o]: 328
> 0x00000b7f peer_check_expire [inetpeer.o]: 328
> 0x0004 inet_initpeers [inetpeer.o]: 112
> text data bss dec hex filename
> 5163 432 21 5616 15f0 net/ipv4/inetpeer.o
>
> Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
> Cc: Scot Doyle <lkml@scotdoyle.com>
> Cc: Stephen Hemminger <shemminger@vyatta.com>
> Cc: Hiroaki SHIMODA <shimoda.hiroaki@gmail.com>
> Reviewed-by: Hiroaki SHIMODA <shimoda.hiroaki@gmail.com>
> Signed-off-by: David S. Miller <davem@davemloft.net>
> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
> Signed-off-by: Tim Gardner <tim.gardner@canonical.com>
>
> CVE-2011-4087
> Signed-off-by: Andy Whitcroft <apw@canonical.com>
> ---
> net/ipv4/inetpeer.c | 13 +++++++------
> 1 files changed, 7 insertions(+), 6 deletions(-)
>
> diff --git a/net/ipv4/inetpeer.c b/net/ipv4/inetpeer.c
> index f231d1d..824e5f1 100644
> --- a/net/ipv4/inetpeer.c
> +++ b/net/ipv4/inetpeer.c
> @@ -367,7 +367,8 @@ static void inetpeer_free_rcu(struct rcu_head *head)
> }
>
> /* May be called with local BH enabled. */
> -static void unlink_from_pool(struct inet_peer *p, struct inet_peer_base *base)
> +static void unlink_from_pool(struct inet_peer *p, struct inet_peer_base *base,
> + struct inet_peer __rcu **stack[PEER_MAXDEPTH])
> {
> int do_free;
>
> @@ -381,7 +382,6 @@ static void unlink_from_pool(struct inet_peer *p, struct inet_peer_base *base)
> * We use refcnt=-1 to alert lockless readers this entry is deleted.
> */
> if (atomic_cmpxchg(&p->refcnt, 1, -1) == 1) {
> - struct inet_peer __rcu **stack[PEER_MAXDEPTH];
> struct inet_peer __rcu ***stackptr, ***delp;
> if (lookup(&p->daddr, stack, base) != p)
> BUG();
> @@ -436,7 +436,7 @@ static struct inet_peer_base *peer_to_base(struct inet_peer *p)
> }
>
> /* May be called with local BH enabled. */
> -static int cleanup_once(unsigned long ttl)
> +static int cleanup_once(unsigned long ttl, struct inet_peer __rcu **stack[PEER_MAXDEPTH])
> {
> struct inet_peer *p = NULL;
>
> @@ -468,7 +468,7 @@ static int cleanup_once(unsigned long ttl)
> * happen because of entry limits in route cache. */
> return -1;
>
> - unlink_from_pool(p, peer_to_base(p));
> + unlink_from_pool(p, peer_to_base(p), stack);
> return 0;
> }
>
> @@ -524,7 +524,7 @@ struct inet_peer *inet_getpeer(struct inetpeer_addr *daddr, int create)
>
> if (base->total >= inet_peer_threshold)
> /* Remove one less-recently-used entry. */
> - cleanup_once(0);
> + cleanup_once(0, stack);
>
> return p;
> }
> @@ -540,6 +540,7 @@ static void peer_check_expire(unsigned long dummy)
> {
> unsigned long now = jiffies;
> int ttl, total;
> + struct inet_peer __rcu **stack[PEER_MAXDEPTH];
>
> total = compute_total();
> if (total >= inet_peer_threshold)
> @@ -548,7 +549,7 @@ static void peer_check_expire(unsigned long dummy)
> ttl = inet_peer_maxttl
> - (inet_peer_maxttl - inet_peer_minttl) / HZ *
> total / inet_peer_threshold * HZ;
> - while (!cleanup_once(ttl)) {
> + while (!cleanup_once(ttl, stack)) {
> if (jiffies != now)
> break;
> }

Not really sure how the stack saving helps, but it is matching the upstream
change (while the upstream code already looks completely different, ugh). And it
seems safe as inet_getpeer uses its local array and the call of unlink_from_pool
is last in cleanup_once...

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