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Message-ID: <20070910214712.GI11801@linux.vnet.ibm.com>
Date: Mon, 10 Sep 2007 14:47:12 -0700
From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To: Vlad Yasevich <vladislav.yasevich@...com>
Cc: netdev@...r.kernel.org, lksctp-developers@...ts.sourceforge.net
Subject: Re: [RFC PATCH 1/2] SCTP: Add RCU synchronization around sctp_localaddr_list
On Mon, Sep 10, 2007 at 03:46:29PM -0400, Vlad Yasevich wrote:
> sctp_localaddr_list is modified dynamically via NETDEV_UP
> and NETDEV_DOWN events, but there is not synchronization
> between writer (even handler) and readers. As a result,
> the readers can access an entry that has been freed and
> crash the sytem.
Good start, but few questions interspersed below...
Thanx, Paul
> Signed-off-by: Vlad Yasevich <vladislav.yasevich@...com>
> ---
> include/net/sctp/sctp.h | 1 +
> include/net/sctp/structs.h | 2 +
> net/sctp/bind_addr.c | 2 +
> net/sctp/ipv6.c | 33 ++++++++++++++++++++--------
> net/sctp/protocol.c | 50 ++++++++++++++++++++++++++++++-------------
> net/sctp/socket.c | 38 ++++++++++++++++++++++-----------
> 6 files changed, 88 insertions(+), 38 deletions(-)
>
> diff --git a/include/net/sctp/sctp.h b/include/net/sctp/sctp.h
> index d529045..c9cc00c 100644
> --- a/include/net/sctp/sctp.h
> +++ b/include/net/sctp/sctp.h
> @@ -123,6 +123,7 @@
> * sctp/protocol.c
> */
> extern struct sock *sctp_get_ctl_sock(void);
> +extern void sctp_local_addr_free(struct rcu_head *head);
> extern int sctp_copy_local_addr_list(struct sctp_bind_addr *,
> sctp_scope_t, gfp_t gfp,
> int flags);
> diff --git a/include/net/sctp/structs.h b/include/net/sctp/structs.h
> index c0d5848..2591c49 100644
> --- a/include/net/sctp/structs.h
> +++ b/include/net/sctp/structs.h
> @@ -737,8 +737,10 @@ const union sctp_addr *sctp_source(const struct sctp_chunk *chunk);
> /* This is a structure for holding either an IPv6 or an IPv4 address. */
> struct sctp_sockaddr_entry {
> struct list_head list;
> + struct rcu_head rcu;
> union sctp_addr a;
> __u8 use_as_src;
> + __u8 valid;
> };
>
> typedef struct sctp_chunk *(sctp_packet_phandler_t)(struct sctp_association *);
> diff --git a/net/sctp/bind_addr.c b/net/sctp/bind_addr.c
> index fdb287a..7fc369f 100644
> --- a/net/sctp/bind_addr.c
> +++ b/net/sctp/bind_addr.c
> @@ -163,8 +163,10 @@ int sctp_add_bind_addr(struct sctp_bind_addr *bp, union sctp_addr *new,
> addr->a.v4.sin_port = htons(bp->port);
>
> addr->use_as_src = use_as_src;
> + addr->valid = 1;
>
> INIT_LIST_HEAD(&addr->list);
> + INIT_RCU_HEAD(&addr->rcu);
> list_add_tail(&addr->list, &bp->address_list);
> SCTP_DBG_OBJCNT_INC(addr);
>
> diff --git a/net/sctp/ipv6.c b/net/sctp/ipv6.c
> index f8aa23d..fc2e4e2 100644
> --- a/net/sctp/ipv6.c
> +++ b/net/sctp/ipv6.c
> @@ -77,13 +77,18 @@
>
> #include <asm/uaccess.h>
>
> -/* Event handler for inet6 address addition/deletion events. */
> +/* Event handler for inet6 address addition/deletion events.
> + * This even is part of the atomic notifier call chain
> + * and thus happens atomically and can NOT sleep. As a result
> + * we can't and really don't need to add any locks to guard the
> + * RCU.
> + */
> static int sctp_inet6addr_event(struct notifier_block *this, unsigned long ev,
> void *ptr)
> {
> struct inet6_ifaddr *ifa = (struct inet6_ifaddr *)ptr;
> - struct sctp_sockaddr_entry *addr;
> - struct list_head *pos, *temp;
> + struct sctp_sockaddr_entry *addr = NULL;
> + struct sctp_sockaddr_entry *temp;
>
> switch (ev) {
> case NETDEV_UP:
> @@ -94,19 +99,26 @@ static int sctp_inet6addr_event(struct notifier_block *this, unsigned long ev,
> memcpy(&addr->a.v6.sin6_addr, &ifa->addr,
> sizeof(struct in6_addr));
> addr->a.v6.sin6_scope_id = ifa->idev->dev->ifindex;
> - list_add_tail(&addr->list, &sctp_local_addr_list);
> + addr->valid = 1;
> + rcu_read_lock();
> + list_add_tail_rcu(&addr->list, &sctp_local_addr_list);
> + rcu_read_unlock();
If we are under the protection of the update-side mutex, the rcu_read_lock()
and rcu_read_unlock() are (harmlessly) redundant. If we are not under
the protection of some mutex, what prevents concurrent list_add_tail_rcu()
calls from messing up the sctp_sockaddr_entry list?
> }
> break;
> case NETDEV_DOWN:
> - list_for_each_safe(pos, temp, &sctp_local_addr_list) {
> - addr = list_entry(pos, struct sctp_sockaddr_entry, list);
> - if (ipv6_addr_equal(&addr->a.v6.sin6_addr, &ifa->addr)) {
> - list_del(pos);
> - kfree(addr);
> + rcu_read_lock();
> + list_for_each_entry_safe(addr, temp,
> + &sctp_local_addr_list, list) {
> + if (ipv6_addr_equal(&addr->a.v6.sin6_addr,
> + &ifa->addr)) {
> + addr->valid = 0;
> + list_del_rcu(&addr->list);
> break;
> }
> }
> -
> + rcu_read_unlock();
> + if (addr && !addr->valid)
> + call_rcu(&addr->rcu, sctp_local_addr_free);
Are we under the protection of the update-side lock here? If not,
what prevents two different tasks from executing this in parallel,
potentially tangling both the list that the sctp_sockaddr_entry list and
the internal RCU lists? (It is forbidden to call_rcu() a given element
twice concurrently.)
If we are in fact under the protection of the update-side lock, the
rcu_read_lock() and rcu_read_unlock() pairs are redundant (though this
is harmless, aside from the (small) potential for confusion).
> break;
> }
>
> @@ -368,6 +380,7 @@ static void sctp_v6_copy_addrlist(struct list_head *addrlist,
> addr->a.v6.sin6_addr = ifp->addr;
> addr->a.v6.sin6_scope_id = dev->ifindex;
> INIT_LIST_HEAD(&addr->list);
> + INIT_RCU_HEAD(&addr->rcu);
> list_add_tail(&addr->list, addrlist);
> }
> }
> diff --git a/net/sctp/protocol.c b/net/sctp/protocol.c
> index e98579b..ac52f9e 100644
> --- a/net/sctp/protocol.c
> +++ b/net/sctp/protocol.c
> @@ -153,6 +153,7 @@ static void sctp_v4_copy_addrlist(struct list_head *addrlist,
> addr->a.v4.sin_family = AF_INET;
> addr->a.v4.sin_port = 0;
> addr->a.v4.sin_addr.s_addr = ifa->ifa_local;
> + INIT_RCU_HEAD(&addr->rcu);
> list_add_tail(&addr->list, addrlist);
> }
> }
> @@ -192,16 +193,24 @@ static void sctp_free_local_addr_list(void)
> }
> }
>
> +void sctp_local_addr_free(struct rcu_head *head)
> +{
> + struct sctp_sockaddr_entry *e = container_of(head,
> + struct sctp_sockaddr_entry, rcu);
> + kfree(e);
> +}
> +
> /* Copy the local addresses which are valid for 'scope' into 'bp'. */
> int sctp_copy_local_addr_list(struct sctp_bind_addr *bp, sctp_scope_t scope,
> gfp_t gfp, int copy_flags)
> {
> struct sctp_sockaddr_entry *addr;
> int error = 0;
> - struct list_head *pos, *temp;
>
> - list_for_each_safe(pos, temp, &sctp_local_addr_list) {
> - addr = list_entry(pos, struct sctp_sockaddr_entry, list);
> + rcu_read_lock();
> + list_for_each_entry_rcu(addr, &sctp_local_addr_list, list) {
> + if (!addr->valid)
> + continue;
What happens if the update-side code removes the element from the list
and marks it !->valid right here?
If this turns out to be harmless, why not just dispense with the ->valid
flag entirely?
> if (sctp_in_scope(&addr->a, scope)) {
> /* Now that the address is in scope, check to see if
> * the address type is really supported by the local
> @@ -221,6 +230,7 @@ int sctp_copy_local_addr_list(struct sctp_bind_addr *bp, sctp_scope_t scope,
> }
>
> end_copy:
> + rcu_read_unlock();
> return error;
> }
>
> @@ -600,13 +610,17 @@ static void sctp_v4_seq_dump_addr(struct seq_file *seq, union sctp_addr *addr)
> seq_printf(seq, "%d.%d.%d.%d ", NIPQUAD(addr->v4.sin_addr));
> }
>
> -/* Event handler for inet address addition/deletion events. */
> +/* Event handler for inet address addition/deletion events.
> + * This is part of the blocking notifier call chain that is
> + * guarted by a mutex. As a result we don't need to add
> + * any additional guards for the RCU
> + */
> static int sctp_inetaddr_event(struct notifier_block *this, unsigned long ev,
> void *ptr)
> {
> struct in_ifaddr *ifa = (struct in_ifaddr *)ptr;
> - struct sctp_sockaddr_entry *addr;
> - struct list_head *pos, *temp;
> + struct sctp_sockaddr_entry *addr = NULL;
> + struct sctp_sockaddr_entry *temp;
>
> switch (ev) {
> case NETDEV_UP:
> @@ -615,19 +629,25 @@ static int sctp_inetaddr_event(struct notifier_block *this, unsigned long ev,
> addr->a.v4.sin_family = AF_INET;
> addr->a.v4.sin_port = 0;
> addr->a.v4.sin_addr.s_addr = ifa->ifa_local;
> - list_add_tail(&addr->list, &sctp_local_addr_list);
> + addr->valid = 1;
> + rcu_read_lock();
> + list_add_tail_rcu(&addr->list, &sctp_local_addr_list);
> + rcu_read_unlock();
Based on the additions to the header comment, I am assuming that we
hold an update-side mutex. This means that the rcu_read_lock() and
rcu_read_unlock() are (harmlessly) redundant.
> }
> break;
> case NETDEV_DOWN:
> - list_for_each_safe(pos, temp, &sctp_local_addr_list) {
> - addr = list_entry(pos, struct sctp_sockaddr_entry, list);
> + rcu_read_lock();
> + list_for_each_entry_safe(addr, temp,
> + &sctp_local_addr_list, list) {
> if (addr->a.v4.sin_addr.s_addr == ifa->ifa_local) {
> - list_del(pos);
> - kfree(addr);
> + addr->valid = 0;
> + list_del_rcu(&addr->list);
> break;
> }
> }
> -
> + rcu_read_unlock();
Ditto.
> + if (addr && !addr->valid)
> + call_rcu(&addr->rcu, sctp_local_addr_free);
This one is OK, since we hold the update-side mutex.
> break;
> }
>
> @@ -1227,6 +1247,9 @@ SCTP_STATIC __exit void sctp_exit(void)
> sctp_v6_del_protocol();
> inet_del_protocol(&sctp_protocol, IPPROTO_SCTP);
>
> + /* Unregister notifier for inet address additions/deletions. */
> + unregister_inetaddr_notifier(&sctp_inetaddr_notifier);
> +
> /* Free the local address list. */
> sctp_free_local_addr_list();
>
> @@ -1240,9 +1263,6 @@ SCTP_STATIC __exit void sctp_exit(void)
> inet_unregister_protosw(&sctp_stream_protosw);
> inet_unregister_protosw(&sctp_seqpacket_protosw);
>
> - /* Unregister notifier for inet address additions/deletions. */
> - unregister_inetaddr_notifier(&sctp_inetaddr_notifier);
> -
> sctp_sysctl_unregister();
> list_del(&sctp_ipv4_specific.list);
>
> diff --git a/net/sctp/socket.c b/net/sctp/socket.c
> index 3335460..a3acf78 100644
> --- a/net/sctp/socket.c
> +++ b/net/sctp/socket.c
> @@ -4057,9 +4057,9 @@ static int sctp_getsockopt_local_addrs_num_old(struct sock *sk, int len,
> int __user *optlen)
> {
> sctp_assoc_t id;
> + struct list_head *pos;
> struct sctp_bind_addr *bp;
> struct sctp_association *asoc;
> - struct list_head *pos, *temp;
> struct sctp_sockaddr_entry *addr;
> rwlock_t *addr_lock;
> int cnt = 0;
> @@ -4096,15 +4096,19 @@ static int sctp_getsockopt_local_addrs_num_old(struct sock *sk, int len,
> addr = list_entry(bp->address_list.next,
> struct sctp_sockaddr_entry, list);
> if (sctp_is_any(&addr->a)) {
> - list_for_each_safe(pos, temp, &sctp_local_addr_list) {
> - addr = list_entry(pos,
> - struct sctp_sockaddr_entry,
> - list);
> + rcu_read_lock();
> + list_for_each_entry_rcu(addr,
> + &sctp_local_addr_list, list) {
> + if (!addr->valid)
> + continue;
> +
Again, what happens if the element is deleted just at this point?
If harmless, might be good to get rid of ->valid.
> if ((PF_INET == sk->sk_family) &&
> (AF_INET6 == addr->a.sa.sa_family))
> continue;
> +
> cnt++;
> }
> + rcu_read_unlock();
We are just counting these things, right? If on the other hand we are
keeping a reference outside of rcu_read_lock() protection, then there
needs to be some explicit mechanism preventing the corresponding entry
from being freed.
> } else {
> cnt = 1;
> }
> @@ -4127,14 +4131,16 @@ static int sctp_copy_laddrs_old(struct sock *sk, __u16 port,
> int max_addrs, void *to,
> int *bytes_copied)
> {
> - struct list_head *pos, *next;
> struct sctp_sockaddr_entry *addr;
> union sctp_addr temp;
> int cnt = 0;
> int addrlen;
>
> - list_for_each_safe(pos, next, &sctp_local_addr_list) {
> - addr = list_entry(pos, struct sctp_sockaddr_entry, list);
> + rcu_read_lock();
> + list_for_each_entry_rcu(addr, &sctp_local_addr_list, list) {
> + if (!addr->valid)
> + continue;
> +
Same question as before -- what happens if the element is deleted by some
other CPU (thus clearing ->valid) just at this point?
> if ((PF_INET == sk->sk_family) &&
> (AF_INET6 == addr->a.sa.sa_family))
> continue;
> @@ -4149,6 +4155,7 @@ static int sctp_copy_laddrs_old(struct sock *sk, __u16 port,
> cnt ++;
> if (cnt >= max_addrs) break;
> }
> + rcu_read_unlock();
>
> return cnt;
> }
> @@ -4156,14 +4163,16 @@ static int sctp_copy_laddrs_old(struct sock *sk, __u16 port,
> static int sctp_copy_laddrs(struct sock *sk, __u16 port, void *to,
> size_t space_left, int *bytes_copied)
> {
> - struct list_head *pos, *next;
> struct sctp_sockaddr_entry *addr;
> union sctp_addr temp;
> int cnt = 0;
> int addrlen;
>
> - list_for_each_safe(pos, next, &sctp_local_addr_list) {
> - addr = list_entry(pos, struct sctp_sockaddr_entry, list);
> + rcu_read_lock();
> + list_for_each_entry_rcu(addr, &sctp_local_addr_list, list) {
> + if (!addr->valid)
> + continue;
> +
And the same question here as well...
> if ((PF_INET == sk->sk_family) &&
> (AF_INET6 == addr->a.sa.sa_family))
> continue;
> @@ -4171,8 +4180,10 @@ static int sctp_copy_laddrs(struct sock *sk, __u16 port, void *to,
> sctp_get_pf_specific(sk->sk_family)->addr_v4map(sctp_sk(sk),
> &temp);
> addrlen = sctp_get_af_specific(temp.sa.sa_family)->sockaddr_len;
> - if (space_left < addrlen)
> - return -ENOMEM;
> + if (space_left < addrlen) {
> + cnt = -ENOMEM;
> + break;
> + }
> memcpy(to, &temp, addrlen);
>
> to += addrlen;
> @@ -4180,6 +4191,7 @@ static int sctp_copy_laddrs(struct sock *sk, __u16 port, void *to,
> space_left -= addrlen;
> *bytes_copied += addrlen;
> }
> + rcu_read_unlock();
>
> return cnt;
> }
> --
> 1.5.2.4
>
> -
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