[PATCH v3] 9p: Add refcount to p9_req_t

[PATCH v3] 9p: Add refcount to p9_req_t

[Dominique Martinet]

From: Tomas Bortoli <tomasbortoli@gmail.com>

To avoid use-after-free(s), use a refcount to keep track of the
usable references to any instantiated struct p9_req_t.

This commit adds p9_req_put(), p9_req_get() and p9_req_try_get() as
wrappers to kref_put(), kref_get() and kref_get_unless_zero().
These are used by the client and the transports to keep track of
valid requests' references.

p9_free_req() is added back and used as callback by kref_put().

Add SLAB_TYPESAFE_BY_RCU as it ensures that the memory freed by
kmem_cache_free() will not be reused for another type until the rcu
synchronisation period is over, so an address gotten under rcu read
lock is safe to inc_ref() without corrupting random memory while
the lock is held.

Co-developed-by: Dominique Martinet <dominique.martinet@cea.fr>
Signed-off-by: Tomas Bortoli <tomasbortoli@gmail.com>
Reported-by: syzbot+467050c1ce275af2a5b8@syzkaller.appspotmail.com
Signed-off-by: Dominique Martinet <dominique.martinet@cea.fr>
---
 include/net/9p/client.h | 14 ++++++++++
 net/9p/client.c         | 59 ++++++++++++++++++++++++++++++++++++-----
 net/9p/trans_fd.c       | 11 +++++++-
 net/9p/trans_rdma.c     |  2 ++
 net/9p/trans_virtio.c   | 18 ++++++++++---
 5 files changed, 92 insertions(+), 12 deletions(-)

diff --git a/include/net/9p/client.h b/include/net/9p/client.h
index 735f3979d559..947a570307a6 100644
--- a/include/net/9p/client.h
+++ b/include/net/9p/client.h
@@ -94,6 +94,7 @@ enum p9_req_status_t {
 struct p9_req_t {
 	int status;
 	int t_err;
+	struct kref refcount;
 	wait_queue_head_t wq;
 	struct p9_fcall tc;
 	struct p9_fcall rc;
@@ -233,6 +234,19 @@ int p9_client_lock_dotl(struct p9_fid *fid, struct p9_flock *flock, u8 *status);
 int p9_client_getlock_dotl(struct p9_fid *fid, struct p9_getlock *fl);
 void p9_fcall_fini(struct p9_fcall *fc);
 struct p9_req_t *p9_tag_lookup(struct p9_client *, u16);
+
+static inline void p9_req_get(struct p9_req_t *r)
+{
+	kref_get(&r->refcount);
+}
+
+static inline int p9_req_try_get(struct p9_req_t *r)
+{
+	return kref_get_unless_zero(&r->refcount);
+}
+
+int p9_req_put(struct p9_req_t *r);
+
 void p9_client_cb(struct p9_client *c, struct p9_req_t *req, int status);
 
 int p9_parse_header(struct p9_fcall *, int32_t *, int8_t *, int16_t *, int);
diff --git a/net/9p/client.c b/net/9p/client.c
index 7942c0bfcc5b..4cf11adad819 100644
--- a/net/9p/client.c
+++ b/net/9p/client.c
@@ -310,6 +310,18 @@ p9_tag_alloc(struct p9_client *c, int8_t type, unsigned int max_size)
 	if (tag < 0)
 		goto free;
 
+	/* Init ref to two because in the general case there is one ref
+	 * that is put asynchronously by a writer thread, one ref
+	 * temporarily given by p9_tag_lookup and put by p9_client_cb
+	 * in the recv thread, and one ref put by p9_tag_remove in the
+	 * main thread. The only exception is virtio that does not use
+	 * p9_tag_lookup but does not have a writer thread either
+	 * (the write happens synchronously in the request/zc_request
+	 * callback), so p9_client_cb eats the second ref there
+	 * as the pointer is duplicated directly by virtqueue_add_sgs()
+	 */
+	refcount_set(&req->refcount.refcount, 2);
+
 	return req;
 
 free:
@@ -333,10 +345,21 @@ struct p9_req_t *p9_tag_lookup(struct p9_client *c, u16 tag)
 	struct p9_req_t *req;
 
 	rcu_read_lock();
+again:
 	req = idr_find(&c->reqs, tag);
-	/* There's no refcount on the req; a malicious server could cause
-	 * us to dereference a NULL pointer
-	 */
+	if (req) {
+		/* We have to be careful with the req found under rcu_read_lock
+		 * Thanks to SLAB_TYPESAFE_BY_RCU we can safely try to get the
+		 * ref again without corrupting other data, then check again
+		 * that the tag matches once we have the ref
+		 */
+		if (!p9_req_try_get(req))
+			goto again;
+		if (req->tc.tag != tag) {
+			p9_req_put(req);
+			goto again;
+		}
+	}
 	rcu_read_unlock();
 
 	return req;
@@ -350,7 +373,7 @@ EXPORT_SYMBOL(p9_tag_lookup);
  *
  * Context: Any context.
  */
-static void p9_tag_remove(struct p9_client *c, struct p9_req_t *r)
+static int p9_tag_remove(struct p9_client *c, struct p9_req_t *r)
 {
 	unsigned long flags;
 	u16 tag = r->tc.tag;
@@ -359,11 +382,23 @@ static void p9_tag_remove(struct p9_client *c, struct p9_req_t *r)
 	spin_lock_irqsave(&c->lock, flags);
 	idr_remove(&c->reqs, tag);
 	spin_unlock_irqrestore(&c->lock, flags);
+	return p9_req_put(r);
+}
+
+static void p9_req_free(struct kref *ref)
+{
+	struct p9_req_t *r = container_of(ref, struct p9_req_t, refcount);
 	p9_fcall_fini(&r->tc);
 	p9_fcall_fini(&r->rc);
 	kmem_cache_free(p9_req_cache, r);
 }
 
+int p9_req_put(struct p9_req_t *r)
+{
+	return kref_put(&r->refcount, p9_req_free);
+}
+EXPORT_SYMBOL(p9_req_put);
+
 /**
  * p9_tag_cleanup - cleans up tags structure and reclaims resources
  * @c:  v9fs client struct
@@ -379,7 +414,9 @@ static void p9_tag_cleanup(struct p9_client *c)
 	rcu_read_lock();
 	idr_for_each_entry(&c->reqs, req, id) {
 		pr_info("Tag %d still in use\n", id);
-		p9_tag_remove(c, req);
+		if (p9_tag_remove(c, req) == 0)
+			pr_warn("Packet with tag %d has still references",
+				req->tc.tag);
 	}
 	rcu_read_unlock();
 }
@@ -403,6 +440,7 @@ void p9_client_cb(struct p9_client *c, struct p9_req_t *req, int status)
 
 	wake_up(&req->wq);
 	p9_debug(P9_DEBUG_MUX, "wakeup: %d\n", req->tc.tag);
+	p9_req_put(req);
 }
 EXPORT_SYMBOL(p9_client_cb);
 
@@ -643,9 +681,12 @@ static int p9_client_flush(struct p9_client *c, struct p9_req_t *oldreq)
 	 * if we haven't received a response for oldreq,
 	 * remove it from the list
 	 */
-	if (oldreq->status == REQ_STATUS_SENT)
+	if (oldreq->status == REQ_STATUS_SENT) {
 		if (c->trans_mod->cancelled)
 			c->trans_mod->cancelled(c, oldreq);
+		else
+			p9_req_put(oldreq);
+	}
 
 	p9_tag_remove(c, req);
 	return 0;
@@ -682,6 +723,8 @@ static struct p9_req_t *p9_client_prepare_req(struct p9_client *c,
 	return req;
 reterr:
 	p9_tag_remove(c, req);
+	/* We have to put also the 2nd reference as it won't be used */
+	p9_req_put(req);
 	return ERR_PTR(err);
 }
 
@@ -716,6 +759,8 @@ p9_client_rpc(struct p9_client *c, int8_t type, const char *fmt, ...)
 
 	err = c->trans_mod->request(c, req);
 	if (err < 0) {
+		/* write won't happen */
+		p9_req_put(req);
 		if (err != -ERESTARTSYS && err != -EFAULT)
 			c->status = Disconnected;
 		goto recalc_sigpending;
@@ -2241,7 +2286,7 @@ EXPORT_SYMBOL(p9_client_readlink);
 
 int __init p9_client_init(void)
 {
-	p9_req_cache = KMEM_CACHE(p9_req_t, 0);
+	p9_req_cache = KMEM_CACHE(p9_req_t, SLAB_TYPESAFE_BY_RCU);
 	return p9_req_cache ? 0 : -ENOMEM;
 }
 
diff --git a/net/9p/trans_fd.c b/net/9p/trans_fd.c
index 20f46f13fe83..686e24e355d0 100644
--- a/net/9p/trans_fd.c
+++ b/net/9p/trans_fd.c
@@ -132,6 +132,7 @@ struct p9_conn {
 	struct list_head req_list;
 	struct list_head unsent_req_list;
 	struct p9_req_t *req;
+	struct p9_req_t *wreq;
 	char tmp_buf[7];
 	struct p9_fcall rc;
 	int wpos;
@@ -383,6 +384,7 @@ static void p9_read_work(struct work_struct *work)
 		m->rc.sdata = NULL;
 		m->rc.offset = 0;
 		m->rc.capacity = 0;
+		p9_req_put(m->req);
 		m->req = NULL;
 	}
 
@@ -472,6 +474,8 @@ static void p9_write_work(struct work_struct *work)
 		m->wbuf = req->tc.sdata;
 		m->wsize = req->tc.size;
 		m->wpos = 0;
+		p9_req_get(req);
+		m->wreq = req;
 		spin_unlock(&m->client->lock);
 	}
 
@@ -492,8 +496,11 @@ static void p9_write_work(struct work_struct *work)
 	}
 
 	m->wpos += err;
-	if (m->wpos == m->wsize)
+	if (m->wpos == m->wsize) {
 		m->wpos = m->wsize = 0;
+		p9_req_put(m->wreq);
+		m->wreq = NULL;
+	}
 
 end_clear:
 	clear_bit(Wworksched, &m->wsched);
@@ -694,6 +701,7 @@ static int p9_fd_cancel(struct p9_client *client, struct p9_req_t *req)
 	if (req->status == REQ_STATUS_UNSENT) {
 		list_del(&req->req_list);
 		req->status = REQ_STATUS_FLSHD;
+		p9_req_put(req);
 		ret = 0;
 	}
 	spin_unlock(&client->lock);
@@ -711,6 +719,7 @@ static int p9_fd_cancelled(struct p9_client *client, struct p9_req_t *req)
 	spin_lock(&client->lock);
 	list_del(&req->req_list);
 	spin_unlock(&client->lock);
+	p9_req_put(req);
 
 	return 0;
 }
diff --git a/net/9p/trans_rdma.c b/net/9p/trans_rdma.c
index 5b0cda1aaa7a..9ea9e2eb318e 100644
--- a/net/9p/trans_rdma.c
+++ b/net/9p/trans_rdma.c
@@ -365,6 +365,7 @@ send_done(struct ib_cq *cq, struct ib_wc *wc)
 			    c->busa, c->req->tc.size,
 			    DMA_TO_DEVICE);
 	up(&rdma->sq_sem);
+	p9_req_put(c->req);
 	kfree(c);
 }
 
@@ -611,6 +612,7 @@ static int rdma_cancelled(struct p9_client *client, struct p9_req_t *req)
 {
 	struct p9_trans_rdma *rdma = client->trans;
 	atomic_inc(&rdma->excess_rc);
+	p9_req_put(req);
 	return 0;
 }
 
diff --git a/net/9p/trans_virtio.c b/net/9p/trans_virtio.c
index 3dd6ce1c0f2d..c7aaea74cdc1 100644
--- a/net/9p/trans_virtio.c
+++ b/net/9p/trans_virtio.c
@@ -404,6 +404,7 @@ p9_virtio_zc_request(struct p9_client *client, struct p9_req_t *req,
 	struct scatterlist *sgs[4];
 	size_t offs;
 	int need_drop = 0;
+	int kicked = 0;
 
 	p9_debug(P9_DEBUG_TRANS, "virtio request\n");
 
@@ -411,8 +412,10 @@ p9_virtio_zc_request(struct p9_client *client, struct p9_req_t *req,
 		__le32 sz;
 		int n = p9_get_mapped_pages(chan, &out_pages, uodata,
 					    outlen, &offs, &need_drop);
-		if (n < 0)
-			return n;
+		if (n < 0) {
+			err = n;
+			goto err_out;
+		}
 		out_nr_pages = DIV_ROUND_UP(n + offs, PAGE_SIZE);
 		if (n != outlen) {
 			__le32 v = cpu_to_le32(n);
@@ -428,8 +431,10 @@ p9_virtio_zc_request(struct p9_client *client, struct p9_req_t *req,
 	} else if (uidata) {
 		int n = p9_get_mapped_pages(chan, &in_pages, uidata,
 					    inlen, &offs, &need_drop);
-		if (n < 0)
-			return n;
+		if (n < 0) {
+			err = n;
+			goto err_out;
+		}
 		in_nr_pages = DIV_ROUND_UP(n + offs, PAGE_SIZE);
 		if (n != inlen) {
 			__le32 v = cpu_to_le32(n);
@@ -498,6 +503,7 @@ p9_virtio_zc_request(struct p9_client *client, struct p9_req_t *req,
 	}
 	virtqueue_kick(chan->vq);
 	spin_unlock_irqrestore(&chan->lock, flags);
+	kicked = 1;
 	p9_debug(P9_DEBUG_TRANS, "virtio request kicked\n");
 	err = wait_event_killable(req->wq, req->status >= REQ_STATUS_RCVD);
 	/*
@@ -518,6 +524,10 @@ p9_virtio_zc_request(struct p9_client *client, struct p9_req_t *req,
 	}
 	kvfree(in_pages);
 	kvfree(out_pages);
+	if (!kicked) {
+		/* reply won't come */
+		p9_req_put(req);
+	}
 	return err;
 }
 
-- 
2.17.1

[PATCH v4] 9p: Add refcount to p9_req_t

[Dominique Martinet]

From: Tomas Bortoli <tomasbortoli@gmail.com>

To avoid use-after-free(s), use a refcount to keep track of the
usable references to any instantiated struct p9_req_t.

This commit adds p9_req_put(), p9_req_get() and p9_req_try_get() as
wrappers to kref_put(), kref_get() and kref_get_unless_zero().
These are used by the client and the transports to keep track of
valid requests' references.

p9_free_req() is added back and used as callback by kref_put().

Add SLAB_TYPESAFE_BY_RCU as it ensures that the memory freed by
kmem_cache_free() will not be reused for another type until the rcu
synchronisation period is over, so an address gotten under rcu read
lock is safe to inc_ref() without corrupting random memory while
the lock is held.

Co-developed-by: Dominique Martinet <dominique.martinet@cea.fr>
Signed-off-by: Tomas Bortoli <tomasbortoli@gmail.com>
Reported-by: syzbot+467050c1ce275af2a5b8@syzkaller.appspotmail.com
Signed-off-by: Dominique Martinet <dominique.martinet@cea.fr>
---
v3:
 - add req put if virtio zc request fails
 - add req put if cancelled callback is not defined for virtio
 - (incorrectly) add req put in rdma cancelled callback

v4:
 - removed rdma's cancelled callback put again
 - changed the else if no cancelled callback into actually giving virtio
a callback, xen does not need to call put in that case either because
both function rely on tag_lookup to find the request. trans_fd only
needs to put in cancelled because it also keeps the req in a list around
for cancel.
 - add req put for trans xen's request(), I'm not sure why that one was
missing either..

And with that I believe I am done testing all four transports.
I'll do a second round of tests next week just to make sure, but it
should be good enough™
Sorry for the multiple iterations.

 include/net/9p/client.h | 14 ++++++++++
 net/9p/client.c         | 57 ++++++++++++++++++++++++++++++++++++-----
 net/9p/trans_fd.c       | 11 +++++++-
 net/9p/trans_rdma.c     |  1 +
 net/9p/trans_virtio.c   | 26 ++++++++++++++++---
 net/9p/trans_xen.c      |  1 +
 6 files changed, 98 insertions(+), 12 deletions(-)

diff --git a/include/net/9p/client.h b/include/net/9p/client.h
index 735f3979d559..947a570307a6 100644
--- a/include/net/9p/client.h
+++ b/include/net/9p/client.h
@@ -94,6 +94,7 @@ enum p9_req_status_t {
 struct p9_req_t {
 	int status;
 	int t_err;
+	struct kref refcount;
 	wait_queue_head_t wq;
 	struct p9_fcall tc;
 	struct p9_fcall rc;
@@ -233,6 +234,19 @@ int p9_client_lock_dotl(struct p9_fid *fid, struct p9_flock *flock, u8 *status);
 int p9_client_getlock_dotl(struct p9_fid *fid, struct p9_getlock *fl);
 void p9_fcall_fini(struct p9_fcall *fc);
 struct p9_req_t *p9_tag_lookup(struct p9_client *, u16);
+
+static inline void p9_req_get(struct p9_req_t *r)
+{
+	kref_get(&r->refcount);
+}
+
+static inline int p9_req_try_get(struct p9_req_t *r)
+{
+	return kref_get_unless_zero(&r->refcount);
+}
+
+int p9_req_put(struct p9_req_t *r);
+
 void p9_client_cb(struct p9_client *c, struct p9_req_t *req, int status);
 
 int p9_parse_header(struct p9_fcall *, int32_t *, int8_t *, int16_t *, int);
diff --git a/net/9p/client.c b/net/9p/client.c
index 7942c0bfcc5b..aeeb6d8515d4 100644
--- a/net/9p/client.c
+++ b/net/9p/client.c
@@ -310,6 +310,18 @@ p9_tag_alloc(struct p9_client *c, int8_t type, unsigned int max_size)
 	if (tag < 0)
 		goto free;
 
+	/* Init ref to two because in the general case there is one ref
+	 * that is put asynchronously by a writer thread, one ref
+	 * temporarily given by p9_tag_lookup and put by p9_client_cb
+	 * in the recv thread, and one ref put by p9_tag_remove in the
+	 * main thread. The only exception is virtio that does not use
+	 * p9_tag_lookup but does not have a writer thread either
+	 * (the write happens synchronously in the request/zc_request
+	 * callback), so p9_client_cb eats the second ref there
+	 * as the pointer is duplicated directly by virtqueue_add_sgs()
+	 */
+	refcount_set(&req->refcount.refcount, 2);
+
 	return req;
 
 free:
@@ -333,10 +345,21 @@ struct p9_req_t *p9_tag_lookup(struct p9_client *c, u16 tag)
 	struct p9_req_t *req;
 
 	rcu_read_lock();
+again:
 	req = idr_find(&c->reqs, tag);
-	/* There's no refcount on the req; a malicious server could cause
-	 * us to dereference a NULL pointer
-	 */
+	if (req) {
+		/* We have to be careful with the req found under rcu_read_lock
+		 * Thanks to SLAB_TYPESAFE_BY_RCU we can safely try to get the
+		 * ref again without corrupting other data, then check again
+		 * that the tag matches once we have the ref
+		 */
+		if (!p9_req_try_get(req))
+			goto again;
+		if (req->tc.tag != tag) {
+			p9_req_put(req);
+			goto again;
+		}
+	}
 	rcu_read_unlock();
 
 	return req;
@@ -350,7 +373,7 @@ EXPORT_SYMBOL(p9_tag_lookup);
  *
  * Context: Any context.
  */
-static void p9_tag_remove(struct p9_client *c, struct p9_req_t *r)
+static int p9_tag_remove(struct p9_client *c, struct p9_req_t *r)
 {
 	unsigned long flags;
 	u16 tag = r->tc.tag;
@@ -359,11 +382,23 @@ static void p9_tag_remove(struct p9_client *c, struct p9_req_t *r)
 	spin_lock_irqsave(&c->lock, flags);
 	idr_remove(&c->reqs, tag);
 	spin_unlock_irqrestore(&c->lock, flags);
+	return p9_req_put(r);
+}
+
+static void p9_req_free(struct kref *ref)
+{
+	struct p9_req_t *r = container_of(ref, struct p9_req_t, refcount);
 	p9_fcall_fini(&r->tc);
 	p9_fcall_fini(&r->rc);
 	kmem_cache_free(p9_req_cache, r);
 }
 
+int p9_req_put(struct p9_req_t *r)
+{
+	return kref_put(&r->refcount, p9_req_free);
+}
+EXPORT_SYMBOL(p9_req_put);
+
 /**
  * p9_tag_cleanup - cleans up tags structure and reclaims resources
  * @c:  v9fs client struct
@@ -379,7 +414,9 @@ static void p9_tag_cleanup(struct p9_client *c)
 	rcu_read_lock();
 	idr_for_each_entry(&c->reqs, req, id) {
 		pr_info("Tag %d still in use\n", id);
-		p9_tag_remove(c, req);
+		if (p9_tag_remove(c, req) == 0)
+			pr_warn("Packet with tag %d has still references",
+				req->tc.tag);
 	}
 	rcu_read_unlock();
 }
@@ -403,6 +440,7 @@ void p9_client_cb(struct p9_client *c, struct p9_req_t *req, int status)
 
 	wake_up(&req->wq);
 	p9_debug(P9_DEBUG_MUX, "wakeup: %d\n", req->tc.tag);
+	p9_req_put(req);
 }
 EXPORT_SYMBOL(p9_client_cb);
 
@@ -643,9 +681,10 @@ static int p9_client_flush(struct p9_client *c, struct p9_req_t *oldreq)
 	 * if we haven't received a response for oldreq,
 	 * remove it from the list
 	 */
-	if (oldreq->status == REQ_STATUS_SENT)
+	if (oldreq->status == REQ_STATUS_SENT) {
 		if (c->trans_mod->cancelled)
 			c->trans_mod->cancelled(c, oldreq);
+	}
 
 	p9_tag_remove(c, req);
 	return 0;
@@ -682,6 +721,8 @@ static struct p9_req_t *p9_client_prepare_req(struct p9_client *c,
 	return req;
 reterr:
 	p9_tag_remove(c, req);
+	/* We have to put also the 2nd reference as it won't be used */
+	p9_req_put(req);
 	return ERR_PTR(err);
 }
 
@@ -716,6 +757,8 @@ p9_client_rpc(struct p9_client *c, int8_t type, const char *fmt, ...)
 
 	err = c->trans_mod->request(c, req);
 	if (err < 0) {
+		/* write won't happen */
+		p9_req_put(req);
 		if (err != -ERESTARTSYS && err != -EFAULT)
 			c->status = Disconnected;
 		goto recalc_sigpending;
@@ -2241,7 +2284,7 @@ EXPORT_SYMBOL(p9_client_readlink);
 
 int __init p9_client_init(void)
 {
-	p9_req_cache = KMEM_CACHE(p9_req_t, 0);
+	p9_req_cache = KMEM_CACHE(p9_req_t, SLAB_TYPESAFE_BY_RCU);
 	return p9_req_cache ? 0 : -ENOMEM;
 }
 
diff --git a/net/9p/trans_fd.c b/net/9p/trans_fd.c
index 20f46f13fe83..686e24e355d0 100644
--- a/net/9p/trans_fd.c
+++ b/net/9p/trans_fd.c
@@ -132,6 +132,7 @@ struct p9_conn {
 	struct list_head req_list;
 	struct list_head unsent_req_list;
 	struct p9_req_t *req;
+	struct p9_req_t *wreq;
 	char tmp_buf[7];
 	struct p9_fcall rc;
 	int wpos;
@@ -383,6 +384,7 @@ static void p9_read_work(struct work_struct *work)
 		m->rc.sdata = NULL;
 		m->rc.offset = 0;
 		m->rc.capacity = 0;
+		p9_req_put(m->req);
 		m->req = NULL;
 	}
 
@@ -472,6 +474,8 @@ static void p9_write_work(struct work_struct *work)
 		m->wbuf = req->tc.sdata;
 		m->wsize = req->tc.size;
 		m->wpos = 0;
+		p9_req_get(req);
+		m->wreq = req;
 		spin_unlock(&m->client->lock);
 	}
 
@@ -492,8 +496,11 @@ static void p9_write_work(struct work_struct *work)
 	}
 
 	m->wpos += err;
-	if (m->wpos == m->wsize)
+	if (m->wpos == m->wsize) {
 		m->wpos = m->wsize = 0;
+		p9_req_put(m->wreq);
+		m->wreq = NULL;
+	}
 
 end_clear:
 	clear_bit(Wworksched, &m->wsched);
@@ -694,6 +701,7 @@ static int p9_fd_cancel(struct p9_client *client, struct p9_req_t *req)
 	if (req->status == REQ_STATUS_UNSENT) {
 		list_del(&req->req_list);
 		req->status = REQ_STATUS_FLSHD;
+		p9_req_put(req);
 		ret = 0;
 	}
 	spin_unlock(&client->lock);
@@ -711,6 +719,7 @@ static int p9_fd_cancelled(struct p9_client *client, struct p9_req_t *req)
 	spin_lock(&client->lock);
 	list_del(&req->req_list);
 	spin_unlock(&client->lock);
+	p9_req_put(req);
 
 	return 0;
 }
diff --git a/net/9p/trans_rdma.c b/net/9p/trans_rdma.c
index 5b0cda1aaa7a..9cc9b3a19ee7 100644
--- a/net/9p/trans_rdma.c
+++ b/net/9p/trans_rdma.c
@@ -365,6 +365,7 @@ send_done(struct ib_cq *cq, struct ib_wc *wc)
 			    c->busa, c->req->tc.size,
 			    DMA_TO_DEVICE);
 	up(&rdma->sq_sem);
+	p9_req_put(c->req);
 	kfree(c);
 }
 
diff --git a/net/9p/trans_virtio.c b/net/9p/trans_virtio.c
index 3dd6ce1c0f2d..eb596c2ed546 100644
--- a/net/9p/trans_virtio.c
+++ b/net/9p/trans_virtio.c
@@ -207,6 +207,13 @@ static int p9_virtio_cancel(struct p9_client *client, struct p9_req_t *req)
 	return 1;
 }
 
+/* Reply won't come, so drop req ref */
+static int p9_virtio_cancelled(struct p9_client *client, struct p9_req_t *req)
+{
+	p9_req_put(req);
+	return 0;
+}
+
 /**
  * pack_sg_list_p - Just like pack_sg_list. Instead of taking a buffer,
  * this takes a list of pages.
@@ -404,6 +411,7 @@ p9_virtio_zc_request(struct p9_client *client, struct p9_req_t *req,
 	struct scatterlist *sgs[4];
 	size_t offs;
 	int need_drop = 0;
+	int kicked = 0;
 
 	p9_debug(P9_DEBUG_TRANS, "virtio request\n");
 
@@ -411,8 +419,10 @@ p9_virtio_zc_request(struct p9_client *client, struct p9_req_t *req,
 		__le32 sz;
 		int n = p9_get_mapped_pages(chan, &out_pages, uodata,
 					    outlen, &offs, &need_drop);
-		if (n < 0)
-			return n;
+		if (n < 0) {
+			err = n;
+			goto err_out;
+		}
 		out_nr_pages = DIV_ROUND_UP(n + offs, PAGE_SIZE);
 		if (n != outlen) {
 			__le32 v = cpu_to_le32(n);
@@ -428,8 +438,10 @@ p9_virtio_zc_request(struct p9_client *client, struct p9_req_t *req,
 	} else if (uidata) {
 		int n = p9_get_mapped_pages(chan, &in_pages, uidata,
 					    inlen, &offs, &need_drop);
-		if (n < 0)
-			return n;
+		if (n < 0) {
+			err = n;
+			goto err_out;
+		}
 		in_nr_pages = DIV_ROUND_UP(n + offs, PAGE_SIZE);
 		if (n != inlen) {
 			__le32 v = cpu_to_le32(n);
@@ -498,6 +510,7 @@ p9_virtio_zc_request(struct p9_client *client, struct p9_req_t *req,
 	}
 	virtqueue_kick(chan->vq);
 	spin_unlock_irqrestore(&chan->lock, flags);
+	kicked = 1;
 	p9_debug(P9_DEBUG_TRANS, "virtio request kicked\n");
 	err = wait_event_killable(req->wq, req->status >= REQ_STATUS_RCVD);
 	/*
@@ -518,6 +531,10 @@ p9_virtio_zc_request(struct p9_client *client, struct p9_req_t *req,
 	}
 	kvfree(in_pages);
 	kvfree(out_pages);
+	if (!kicked) {
+		/* reply won't come */
+		p9_req_put(req);
+	}
 	return err;
 }
 
@@ -750,6 +767,7 @@ static struct p9_trans_module p9_virtio_trans = {
 	.request = p9_virtio_request,
 	.zc_request = p9_virtio_zc_request,
 	.cancel = p9_virtio_cancel,
+	.cancelled = p9_virtio_cancelled,
 	/*
 	 * We leave one entry for input and one entry for response
 	 * headers. We also skip one more entry to accomodate, address
diff --git a/net/9p/trans_xen.c b/net/9p/trans_xen.c
index 782a07f2ad0c..e2fbf3677b9b 100644
--- a/net/9p/trans_xen.c
+++ b/net/9p/trans_xen.c
@@ -185,6 +185,7 @@ static int p9_xen_request(struct p9_client *client, struct p9_req_t *p9_req)
 	ring->intf->out_prod = prod;
 	spin_unlock_irqrestore(&ring->lock, flags);
 	notify_remote_via_irq(ring->irq);
+	p9_req_put(p9_req);
 
 	return 0;
 }
-- 
2.17.1

Re: [PATCH v4] 9p: Add refcount to p9_req_t

[Tomas Bortoli]

On 08/30/2018 12:52 PM, Dominique Martinet wrote:
> From: Tomas Bortoli <tomasbortoli@gmail.com>
> 
> To avoid use-after-free(s), use a refcount to keep track of the
> usable references to any instantiated struct p9_req_t.
> 
> This commit adds p9_req_put(), p9_req_get() and p9_req_try_get() as
> wrappers to kref_put(), kref_get() and kref_get_unless_zero().
> These are used by the client and the transports to keep track of
> valid requests' references.
> 
> p9_free_req() is added back and used as callback by kref_put().
> 
> Add SLAB_TYPESAFE_BY_RCU as it ensures that the memory freed by
> kmem_cache_free() will not be reused for another type until the rcu
> synchronisation period is over, so an address gotten under rcu read
> lock is safe to inc_ref() without corrupting random memory while
> the lock is held.
> 
> Co-developed-by: Dominique Martinet <dominique.martinet@cea.fr>
> Signed-off-by: Tomas Bortoli <tomasbortoli@gmail.com>
> Reported-by: syzbot+467050c1ce275af2a5b8@syzkaller.appspotmail.com
> Signed-off-by: Dominique Martinet <dominique.martinet@cea.fr>
> ---
> v3:
>  - add req put if virtio zc request fails
>  - add req put if cancelled callback is not defined for virtio
>  - (incorrectly) add req put in rdma cancelled callback
> 
> v4:
>  - removed rdma's cancelled callback put again
>  - changed the else if no cancelled callback into actually giving virtio
> a callback, xen does not need to call put in that case either because
> both function rely on tag_lookup to find the request. trans_fd only
> needs to put in cancelled because it also keeps the req in a list around
> for cancel.
>  - add req put for trans xen's request(), I'm not sure why that one was
> missing either..
> 
> And with that I believe I am done testing all four transports.
> I'll do a second round of tests next week just to make sure, but it
> should be good enough™
> Sorry for the multiple iterations.
> 
>  include/net/9p/client.h | 14 ++++++++++
>  net/9p/client.c         | 57 ++++++++++++++++++++++++++++++++++++-----
>  net/9p/trans_fd.c       | 11 +++++++-
>  net/9p/trans_rdma.c     |  1 +
>  net/9p/trans_virtio.c   | 26 ++++++++++++++++---
>  net/9p/trans_xen.c      |  1 +
>  6 files changed, 98 insertions(+), 12 deletions(-)
> 
> diff --git a/include/net/9p/client.h b/include/net/9p/client.h
> index 735f3979d559..947a570307a6 100644
> --- a/include/net/9p/client.h
> +++ b/include/net/9p/client.h
> @@ -94,6 +94,7 @@ enum p9_req_status_t {
>  struct p9_req_t {
>  	int status;
>  	int t_err;
> +	struct kref refcount;
>  	wait_queue_head_t wq;
>  	struct p9_fcall tc;
>  	struct p9_fcall rc;
> @@ -233,6 +234,19 @@ int p9_client_lock_dotl(struct p9_fid *fid, struct p9_flock *flock, u8 *status);
>  int p9_client_getlock_dotl(struct p9_fid *fid, struct p9_getlock *fl);
>  void p9_fcall_fini(struct p9_fcall *fc);
>  struct p9_req_t *p9_tag_lookup(struct p9_client *, u16);
> +
> +static inline void p9_req_get(struct p9_req_t *r)
> +{
> +	kref_get(&r->refcount);
> +}
> +
> +static inline int p9_req_try_get(struct p9_req_t *r)
> +{
> +	return kref_get_unless_zero(&r->refcount);
> +}
> +
> +int p9_req_put(struct p9_req_t *r);
> +
>  void p9_client_cb(struct p9_client *c, struct p9_req_t *req, int status);
>  
>  int p9_parse_header(struct p9_fcall *, int32_t *, int8_t *, int16_t *, int);
> diff --git a/net/9p/client.c b/net/9p/client.c
> index 7942c0bfcc5b..aeeb6d8515d4 100644
> --- a/net/9p/client.c
> +++ b/net/9p/client.c
> @@ -310,6 +310,18 @@ p9_tag_alloc(struct p9_client *c, int8_t type, unsigned int max_size)
>  	if (tag < 0)
>  		goto free;
>  
> +	/* Init ref to two because in the general case there is one ref
> +	 * that is put asynchronously by a writer thread, one ref
> +	 * temporarily given by p9_tag_lookup and put by p9_client_cb
> +	 * in the recv thread, and one ref put by p9_tag_remove in the
> +	 * main thread. The only exception is virtio that does not use
> +	 * p9_tag_lookup but does not have a writer thread either
> +	 * (the write happens synchronously in the request/zc_request
> +	 * callback), so p9_client_cb eats the second ref there
> +	 * as the pointer is duplicated directly by virtqueue_add_sgs()
> +	 */
> +	refcount_set(&req->refcount.refcount, 2);
> +
>  	return req;
>  
>  free:
> @@ -333,10 +345,21 @@ struct p9_req_t *p9_tag_lookup(struct p9_client *c, u16 tag)
>  	struct p9_req_t *req;
>  
>  	rcu_read_lock();
> +again:
>  	req = idr_find(&c->reqs, tag);
> -	/* There's no refcount on the req; a malicious server could cause
> -	 * us to dereference a NULL pointer
> -	 */
> +	if (req) {
> +		/* We have to be careful with the req found under rcu_read_lock
> +		 * Thanks to SLAB_TYPESAFE_BY_RCU we can safely try to get the
> +		 * ref again without corrupting other data, then check again
> +		 * that the tag matches once we have the ref
> +		 */
> +		if (!p9_req_try_get(req))
> +			goto again;
> +		if (req->tc.tag != tag) {
> +			p9_req_put(req);
> +			goto again;
> +		}
> +	}
>  	rcu_read_unlock();
>  
>  	return req;
> @@ -350,7 +373,7 @@ EXPORT_SYMBOL(p9_tag_lookup);
>   *
>   * Context: Any context.
>   */
> -static void p9_tag_remove(struct p9_client *c, struct p9_req_t *r)
> +static int p9_tag_remove(struct p9_client *c, struct p9_req_t *r)
>  {
>  	unsigned long flags;
>  	u16 tag = r->tc.tag;
> @@ -359,11 +382,23 @@ static void p9_tag_remove(struct p9_client *c, struct p9_req_t *r)
>  	spin_lock_irqsave(&c->lock, flags);
>  	idr_remove(&c->reqs, tag);
>  	spin_unlock_irqrestore(&c->lock, flags);
> +	return p9_req_put(r);
> +}
> +
> +static void p9_req_free(struct kref *ref)
> +{
> +	struct p9_req_t *r = container_of(ref, struct p9_req_t, refcount);
>  	p9_fcall_fini(&r->tc);
>  	p9_fcall_fini(&r->rc);
>  	kmem_cache_free(p9_req_cache, r);
>  }
>  
> +int p9_req_put(struct p9_req_t *r)
> +{
> +	return kref_put(&r->refcount, p9_req_free);
> +}
> +EXPORT_SYMBOL(p9_req_put);
> +
>  /**
>   * p9_tag_cleanup - cleans up tags structure and reclaims resources
>   * @c:  v9fs client struct
> @@ -379,7 +414,9 @@ static void p9_tag_cleanup(struct p9_client *c)
>  	rcu_read_lock();
>  	idr_for_each_entry(&c->reqs, req, id) {
>  		pr_info("Tag %d still in use\n", id);
> -		p9_tag_remove(c, req);
> +		if (p9_tag_remove(c, req) == 0)
> +			pr_warn("Packet with tag %d has still references",
> +				req->tc.tag);
>  	}
>  	rcu_read_unlock();
>  }
> @@ -403,6 +440,7 @@ void p9_client_cb(struct p9_client *c, struct p9_req_t *req, int status)
>  
>  	wake_up(&req->wq);
>  	p9_debug(P9_DEBUG_MUX, "wakeup: %d\n", req->tc.tag);
> +	p9_req_put(req);
>  }
>  EXPORT_SYMBOL(p9_client_cb);
>  
> @@ -643,9 +681,10 @@ static int p9_client_flush(struct p9_client *c, struct p9_req_t *oldreq)
>  	 * if we haven't received a response for oldreq,
>  	 * remove it from the list
>  	 */
> -	if (oldreq->status == REQ_STATUS_SENT)
> +	if (oldreq->status == REQ_STATUS_SENT) {
>  		if (c->trans_mod->cancelled)
>  			c->trans_mod->cancelled(c, oldreq);
> +	}
>  
>  	p9_tag_remove(c, req);
>  	return 0;
> @@ -682,6 +721,8 @@ static struct p9_req_t *p9_client_prepare_req(struct p9_client *c,
>  	return req;
>  reterr:
>  	p9_tag_remove(c, req);
> +	/* We have to put also the 2nd reference as it won't be used */
> +	p9_req_put(req);
>  	return ERR_PTR(err);
>  }
>  
> @@ -716,6 +757,8 @@ p9_client_rpc(struct p9_client *c, int8_t type, const char *fmt, ...)
>  
>  	err = c->trans_mod->request(c, req);
>  	if (err < 0) {
> +		/* write won't happen */
> +		p9_req_put(req);
>  		if (err != -ERESTARTSYS && err != -EFAULT)
>  			c->status = Disconnected;
>  		goto recalc_sigpending;
> @@ -2241,7 +2284,7 @@ EXPORT_SYMBOL(p9_client_readlink);
>  
>  int __init p9_client_init(void)
>  {
> -	p9_req_cache = KMEM_CACHE(p9_req_t, 0);
> +	p9_req_cache = KMEM_CACHE(p9_req_t, SLAB_TYPESAFE_BY_RCU);
>  	return p9_req_cache ? 0 : -ENOMEM;
>  }
>  
> diff --git a/net/9p/trans_fd.c b/net/9p/trans_fd.c
> index 20f46f13fe83..686e24e355d0 100644
> --- a/net/9p/trans_fd.c
> +++ b/net/9p/trans_fd.c
> @@ -132,6 +132,7 @@ struct p9_conn {
>  	struct list_head req_list;
>  	struct list_head unsent_req_list;
>  	struct p9_req_t *req;
> +	struct p9_req_t *wreq;
>  	char tmp_buf[7];
>  	struct p9_fcall rc;
>  	int wpos;
> @@ -383,6 +384,7 @@ static void p9_read_work(struct work_struct *work)
>  		m->rc.sdata = NULL;
>  		m->rc.offset = 0;
>  		m->rc.capacity = 0;
> +		p9_req_put(m->req);
>  		m->req = NULL;
>  	}
>  
> @@ -472,6 +474,8 @@ static void p9_write_work(struct work_struct *work)
>  		m->wbuf = req->tc.sdata;
>  		m->wsize = req->tc.size;
>  		m->wpos = 0;
> +		p9_req_get(req);
> +		m->wreq = req;
>  		spin_unlock(&m->client->lock);
>  	}
>  
> @@ -492,8 +496,11 @@ static void p9_write_work(struct work_struct *work)
>  	}
>  
>  	m->wpos += err;
> -	if (m->wpos == m->wsize)
> +	if (m->wpos == m->wsize) {
>  		m->wpos = m->wsize = 0;
> +		p9_req_put(m->wreq);
> +		m->wreq = NULL;
> +	}
>  
>  end_clear:
>  	clear_bit(Wworksched, &m->wsched);
> @@ -694,6 +701,7 @@ static int p9_fd_cancel(struct p9_client *client, struct p9_req_t *req)
>  	if (req->status == REQ_STATUS_UNSENT) {
>  		list_del(&req->req_list);
>  		req->status = REQ_STATUS_FLSHD;
> +		p9_req_put(req);
>  		ret = 0;
>  	}
>  	spin_unlock(&client->lock);
> @@ -711,6 +719,7 @@ static int p9_fd_cancelled(struct p9_client *client, struct p9_req_t *req)
>  	spin_lock(&client->lock);
>  	list_del(&req->req_list);
>  	spin_unlock(&client->lock);
> +	p9_req_put(req);
>  
>  	return 0;
>  }
> diff --git a/net/9p/trans_rdma.c b/net/9p/trans_rdma.c
> index 5b0cda1aaa7a..9cc9b3a19ee7 100644
> --- a/net/9p/trans_rdma.c
> +++ b/net/9p/trans_rdma.c
> @@ -365,6 +365,7 @@ send_done(struct ib_cq *cq, struct ib_wc *wc)
>  			    c->busa, c->req->tc.size,
>  			    DMA_TO_DEVICE);
>  	up(&rdma->sq_sem);
> +	p9_req_put(c->req);
>  	kfree(c);
>  }
>  
> diff --git a/net/9p/trans_virtio.c b/net/9p/trans_virtio.c
> index 3dd6ce1c0f2d..eb596c2ed546 100644
> --- a/net/9p/trans_virtio.c
> +++ b/net/9p/trans_virtio.c
> @@ -207,6 +207,13 @@ static int p9_virtio_cancel(struct p9_client *client, struct p9_req_t *req)
>  	return 1;
>  }
>  
> +/* Reply won't come, so drop req ref */
> +static int p9_virtio_cancelled(struct p9_client *client, struct p9_req_t *req)
> +{
> +	p9_req_put(req);
> +	return 0;
> +}
> +
>  /**
>   * pack_sg_list_p - Just like pack_sg_list. Instead of taking a buffer,
>   * this takes a list of pages.
> @@ -404,6 +411,7 @@ p9_virtio_zc_request(struct p9_client *client, struct p9_req_t *req,
>  	struct scatterlist *sgs[4];
>  	size_t offs;
>  	int need_drop = 0;
> +	int kicked = 0;
>  
>  	p9_debug(P9_DEBUG_TRANS, "virtio request\n");
>  
> @@ -411,8 +419,10 @@ p9_virtio_zc_request(struct p9_client *client, struct p9_req_t *req,
>  		__le32 sz;
>  		int n = p9_get_mapped_pages(chan, &out_pages, uodata,
>  					    outlen, &offs, &need_drop);
> -		if (n < 0)
> -			return n;
> +		if (n < 0) {
> +			err = n;
> +			goto err_out;
> +		}
>  		out_nr_pages = DIV_ROUND_UP(n + offs, PAGE_SIZE);
>  		if (n != outlen) {
>  			__le32 v = cpu_to_le32(n);
> @@ -428,8 +438,10 @@ p9_virtio_zc_request(struct p9_client *client, struct p9_req_t *req,
>  	} else if (uidata) {
>  		int n = p9_get_mapped_pages(chan, &in_pages, uidata,
>  					    inlen, &offs, &need_drop);
> -		if (n < 0)
> -			return n;
> +		if (n < 0) {
> +			err = n;
> +			goto err_out;
> +		}
>  		in_nr_pages = DIV_ROUND_UP(n + offs, PAGE_SIZE);
>  		if (n != inlen) {
>  			__le32 v = cpu_to_le32(n);
> @@ -498,6 +510,7 @@ p9_virtio_zc_request(struct p9_client *client, struct p9_req_t *req,
>  	}
>  	virtqueue_kick(chan->vq);
>  	spin_unlock_irqrestore(&chan->lock, flags);
> +	kicked = 1;
>  	p9_debug(P9_DEBUG_TRANS, "virtio request kicked\n");
>  	err = wait_event_killable(req->wq, req->status >= REQ_STATUS_RCVD);
>  	/*
> @@ -518,6 +531,10 @@ p9_virtio_zc_request(struct p9_client *client, struct p9_req_t *req,
>  	}
>  	kvfree(in_pages);
>  	kvfree(out_pages);
> +	if (!kicked) {
> +		/* reply won't come */
> +		p9_req_put(req);
> +	}
>  	return err;
>  }
>  
> @@ -750,6 +767,7 @@ static struct p9_trans_module p9_virtio_trans = {
>  	.request = p9_virtio_request,
>  	.zc_request = p9_virtio_zc_request,
>  	.cancel = p9_virtio_cancel,
> +	.cancelled = p9_virtio_cancelled,
>  	/*
>  	 * We leave one entry for input and one entry for response
>  	 * headers. We also skip one more entry to accomodate, address
> diff --git a/net/9p/trans_xen.c b/net/9p/trans_xen.c
> index 782a07f2ad0c..e2fbf3677b9b 100644
> --- a/net/9p/trans_xen.c
> +++ b/net/9p/trans_xen.c
> @@ -185,6 +185,7 @@ static int p9_xen_request(struct p9_client *client, struct p9_req_t *p9_req)
>  	ring->intf->out_prod = prod;
>  	spin_unlock_irqrestore(&ring->lock, flags);
>  	notify_remote_via_irq(ring->irq);
> +	p9_req_put(p9_req);
>  
>  	return 0;
>  }
> 

LGTM, thanks Dominique!

Tomas

Re: [PATCH v4] 9p: Add refcount to p9_req_t

[Dominique Martinet]

Tomas Bortoli wrote on Fri, Aug 31, 2018:
> On 08/30/2018 12:52 PM, Dominique Martinet wrote:
> > From: Tomas Bortoli <tomasbortoli@gmail.com>
> > 
> > To avoid use-after-free(s), use a refcount to keep track of the
> > usable references to any instantiated struct p9_req_t.
> > 
> > This commit adds p9_req_put(), p9_req_get() and p9_req_try_get() as
> > wrappers to kref_put(), kref_get() and kref_get_unless_zero().
> > These are used by the client and the transports to keep track of
> > valid requests' references.
> > 
> > p9_free_req() is added back and used as callback by kref_put().
> > 
> > Add SLAB_TYPESAFE_BY_RCU as it ensures that the memory freed by
> > kmem_cache_free() will not be reused for another type until the rcu
> > synchronisation period is over, so an address gotten under rcu read
> > lock is safe to inc_ref() without corrupting random memory while
> > the lock is held.
> > 
> > Co-developed-by: Dominique Martinet <dominique.martinet@cea.fr>
> > Signed-off-by: Tomas Bortoli <tomasbortoli@gmail.com>
> > Reported-by: syzbot+467050c1ce275af2a5b8@syzkaller.appspotmail.com
> > Signed-off-by: Dominique Martinet <dominique.martinet@cea.fr>
> > ---
> > v3:
> >  - add req put if virtio zc request fails
> >  - add req put if cancelled callback is not defined for virtio
> >  - (incorrectly) add req put in rdma cancelled callback
> > 
> > v4:
> >  - removed rdma's cancelled callback put again
> >  - changed the else if no cancelled callback into actually giving virtio
> > a callback, xen does not need to call put in that case either because
> > both function rely on tag_lookup to find the request. trans_fd only
> > needs to put in cancelled because it also keeps the req in a list around
> > for cancel.
> >  - add req put for trans xen's request(), I'm not sure why that one was
> > missing either..
> > 
> > And with that I believe I am done testing all four transports.
> > I'll do a second round of tests next week just to make sure, but it
> > should be good enough™
> > Sorry for the multiple iterations.
>
> LGTM, thanks Dominique!

Thanks.

I've pushed this with the other patches to my '9p-next' branch, which
will get merged to linux-next today/tomorrow, so they can soak up some
syzbot testing as well.
That doesn't mean they cannot get reviews anymore, so don't be shy!


Tomas, I didn't see you reply about the 'rename req to rreq' requested
patch for trans_fd, but it's trivial so if you're not going to do it I
will submit something around next week.

-- 
Dominique