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Message-ID: <CAB9dFdsSHwVo6j=+z=4yiTRSJiOeKpFB4QHf6fqrLRuuAa3+JQ@mail.gmail.com>
Date: Tue, 2 Aug 2022 11:54:04 -0300
From: Marc Dionne <marc.dionne@...istor.com>
To: David Howells <dhowells@...hat.com>
Cc: linux-afs@...ts.infradead.org, linux-fsdevel@...r.kernel.org,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] afs: Fix access after dec in put functions
On Fri, Jul 29, 2022 at 1:40 PM David Howells <dhowells@...hat.com> wrote:
>
> Reference-putting functions should not access the object being put after
> decrementing the refcount unless they reduce the refcount to zero.
>
> Fix a couple of instances of this in afs by copying the information to be
> logged by tracepoint to local variables before doing the decrement.
>
> Fixes: 341f741f04be ("afs: Refcount the afs_call struct")
> Fixes: 452181936931 ("afs: Trace afs_server usage")
> Fixes: 977e5f8ed0ab ("afs: Split the usage count on struct afs_server")
> Signed-off-by: David Howells <dhowells@...hat.com>
> cc: Marc Dionne <marc.dionne@...istor.com>
> cc: linux-afs@...ts.infradead.org
> ---
>
> fs/afs/cmservice.c | 2 +-
> fs/afs/rxrpc.c | 11 ++++++-----
> fs/afs/server.c | 22 +++++++++++++---------
> include/trace/events/afs.h | 12 ++++++------
> 4 files changed, 26 insertions(+), 21 deletions(-)
>
> diff --git a/fs/afs/cmservice.c b/fs/afs/cmservice.c
> index cedd627e1fae..0a090d614e76 100644
> --- a/fs/afs/cmservice.c
> +++ b/fs/afs/cmservice.c
> @@ -212,7 +212,7 @@ static void SRXAFSCB_CallBack(struct work_struct *work)
> * to maintain cache coherency.
> */
> if (call->server) {
> - trace_afs_server(call->server,
> + trace_afs_server(call->server->debug_id,
> refcount_read(&call->server->ref),
> atomic_read(&call->server->active),
> afs_server_trace_callback);
> diff --git a/fs/afs/rxrpc.c b/fs/afs/rxrpc.c
> index d9acc43cb6f0..d5c4785c862d 100644
> --- a/fs/afs/rxrpc.c
> +++ b/fs/afs/rxrpc.c
> @@ -152,7 +152,7 @@ static struct afs_call *afs_alloc_call(struct afs_net *net,
> call->iter = &call->def_iter;
>
> o = atomic_inc_return(&net->nr_outstanding_calls);
> - trace_afs_call(call, afs_call_trace_alloc, 1, o,
> + trace_afs_call(call->debug_id, afs_call_trace_alloc, 1, o,
> __builtin_return_address(0));
> return call;
> }
> @@ -163,12 +163,13 @@ static struct afs_call *afs_alloc_call(struct afs_net *net,
> void afs_put_call(struct afs_call *call)
> {
> struct afs_net *net = call->net;
> + unsigned int debug_id = call->debug_id;
> bool zero;
> int r, o;
>
> zero = __refcount_dec_and_test(&call->ref, &r);
> o = atomic_read(&net->nr_outstanding_calls);
> - trace_afs_call(call, afs_call_trace_put, r - 1, o,
> + trace_afs_call(debug_id, afs_call_trace_put, r - 1, o,
> __builtin_return_address(0));
>
> if (zero) {
> @@ -186,7 +187,7 @@ void afs_put_call(struct afs_call *call)
> afs_put_addrlist(call->alist);
> kfree(call->request);
>
> - trace_afs_call(call, afs_call_trace_free, 0, o,
> + trace_afs_call(call->debug_id, afs_call_trace_free, 0, o,
> __builtin_return_address(0));
> kfree(call);
>
> @@ -203,7 +204,7 @@ static struct afs_call *afs_get_call(struct afs_call *call,
>
> __refcount_inc(&call->ref, &r);
>
> - trace_afs_call(call, why, r + 1,
> + trace_afs_call(call->debug_id, why, r + 1,
> atomic_read(&call->net->nr_outstanding_calls),
> __builtin_return_address(0));
> return call;
> @@ -677,7 +678,7 @@ static void afs_wake_up_async_call(struct sock *sk, struct rxrpc_call *rxcall,
> call->need_attention = true;
>
> if (__refcount_inc_not_zero(&call->ref, &r)) {
> - trace_afs_call(call, afs_call_trace_wake, r + 1,
> + trace_afs_call(call->debug_id, afs_call_trace_wake, r + 1,
> atomic_read(&call->net->nr_outstanding_calls),
> __builtin_return_address(0));
>
> diff --git a/fs/afs/server.c b/fs/afs/server.c
> index ffed828622b6..bca4b4c55c14 100644
> --- a/fs/afs/server.c
> +++ b/fs/afs/server.c
> @@ -243,7 +243,7 @@ static struct afs_server *afs_alloc_server(struct afs_cell *cell,
> server->rtt = UINT_MAX;
>
> afs_inc_servers_outstanding(net);
> - trace_afs_server(server, 1, 1, afs_server_trace_alloc);
> + trace_afs_server(server->debug_id, 1, 1, afs_server_trace_alloc);
> _leave(" = %p", server);
> return server;
>
> @@ -352,10 +352,12 @@ void afs_servers_timer(struct timer_list *timer)
> struct afs_server *afs_get_server(struct afs_server *server,
> enum afs_server_trace reason)
> {
> + unsigned int a;
> int r;
>
> __refcount_inc(&server->ref, &r);
> - trace_afs_server(server, r + 1, atomic_read(&server->active), reason);
> + a = atomic_read(&server->active);
> + trace_afs_server(server->debug_id, r + 1, a, reason);
> return server;
> }
>
> @@ -372,7 +374,7 @@ static struct afs_server *afs_maybe_use_server(struct afs_server *server,
> return NULL;
>
> a = atomic_inc_return(&server->active);
> - trace_afs_server(server, r + 1, a, reason);
> + trace_afs_server(server->debug_id, r + 1, a, reason);
> return server;
> }
>
> @@ -387,7 +389,7 @@ struct afs_server *afs_use_server(struct afs_server *server, enum afs_server_tra
> __refcount_inc(&server->ref, &r);
> a = atomic_inc_return(&server->active);
>
> - trace_afs_server(server, r + 1, a, reason);
> + trace_afs_server(server->debug_id, r + 1, a, reason);
> return server;
> }
>
> @@ -397,14 +399,16 @@ struct afs_server *afs_use_server(struct afs_server *server, enum afs_server_tra
> void afs_put_server(struct afs_net *net, struct afs_server *server,
> enum afs_server_trace reason)
> {
> + unsigned int a;
> bool zero;
> int r;
>
> if (!server)
> return;
>
> + a = atomic_inc_return(&server->active);
> zero = __refcount_dec_and_test(&server->ref, &r);
> - trace_afs_server(server, r - 1, atomic_read(&server->active), reason);
> + trace_afs_server(server->debug_id, r - 1, a, reason);
Don't you also want to copy server->debug_id into a local variable here?
> if (unlikely(zero))
> __afs_put_server(net, server);
> }
> @@ -441,7 +445,7 @@ static void afs_server_rcu(struct rcu_head *rcu)
> {
> struct afs_server *server = container_of(rcu, struct afs_server, rcu);
>
> - trace_afs_server(server, refcount_read(&server->ref),
> + trace_afs_server(server->debug_id, refcount_read(&server->ref),
> atomic_read(&server->active), afs_server_trace_free);
> afs_put_addrlist(rcu_access_pointer(server->addresses));
> kfree(server);
> @@ -492,7 +496,7 @@ static void afs_gc_servers(struct afs_net *net, struct afs_server *gc_list)
>
> active = atomic_read(&server->active);
> if (active == 0) {
> - trace_afs_server(server, refcount_read(&server->ref),
> + trace_afs_server(server->debug_id, refcount_read(&server->ref),
> active, afs_server_trace_gc);
> next = rcu_dereference_protected(
> server->uuid_next, lockdep_is_held(&net->fs_lock.lock));
> @@ -558,7 +562,7 @@ void afs_manage_servers(struct work_struct *work)
> _debug("manage %pU %u", &server->uuid, active);
>
> if (purging) {
> - trace_afs_server(server, refcount_read(&server->ref),
> + trace_afs_server(server->debug_id, refcount_read(&server->ref),
> active, afs_server_trace_purging);
> if (active != 0)
> pr_notice("Can't purge s=%08x\n", server->debug_id);
> @@ -638,7 +642,7 @@ static noinline bool afs_update_server_record(struct afs_operation *op,
>
> _enter("");
>
> - trace_afs_server(server, refcount_read(&server->ref),
> + trace_afs_server(server->debug_id, refcount_read(&server->ref),
> atomic_read(&server->active),
> afs_server_trace_update);
>
> diff --git a/include/trace/events/afs.h b/include/trace/events/afs.h
> index aa60f42a9763..e9d412d19dbb 100644
> --- a/include/trace/events/afs.h
> +++ b/include/trace/events/afs.h
> @@ -727,10 +727,10 @@ TRACE_EVENT(afs_cb_call,
> );
>
> TRACE_EVENT(afs_call,
> - TP_PROTO(struct afs_call *call, enum afs_call_trace op,
> + TP_PROTO(unsigned int call_debug_id, enum afs_call_trace op,
> int ref, int outstanding, const void *where),
>
> - TP_ARGS(call, op, ref, outstanding, where),
> + TP_ARGS(call_debug_id, op, ref, outstanding, where),
>
> TP_STRUCT__entry(
> __field(unsigned int, call )
> @@ -741,7 +741,7 @@ TRACE_EVENT(afs_call,
> ),
>
> TP_fast_assign(
> - __entry->call = call->debug_id;
> + __entry->call = call_debug_id;
> __entry->op = op;
> __entry->ref = ref;
> __entry->outstanding = outstanding;
> @@ -1433,10 +1433,10 @@ TRACE_EVENT(afs_cb_miss,
> );
>
> TRACE_EVENT(afs_server,
> - TP_PROTO(struct afs_server *server, int ref, int active,
> + TP_PROTO(unsigned int server_debug_id, int ref, int active,
> enum afs_server_trace reason),
>
> - TP_ARGS(server, ref, active, reason),
> + TP_ARGS(server_debug_id, ref, active, reason),
>
> TP_STRUCT__entry(
> __field(unsigned int, server )
> @@ -1446,7 +1446,7 @@ TRACE_EVENT(afs_server,
> ),
>
> TP_fast_assign(
> - __entry->server = server->debug_id;
> + __entry->server = server_debug_id;
> __entry->ref = ref;
> __entry->active = active;
> __entry->reason = reason;
>
>
>
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