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Subject[PATCH v3] 9p: Add refcount to p9_req_t
Date
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
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