[PATCH 4.19 45/53] ax25: add refcount in ax25_dev to avoid UAF bugs

Greg Kroah-Hartman
2022-04-26T08:36:56Z

From: Duoming Zhou <duoming@zju.edu.cn>

commit d01ffb9eee4af165d83b08dd73ebdf9fe94a519b upstream.

If we dereference ax25_dev after we call kfree(ax25_dev) in
ax25_dev_device_down(), it will lead to concurrency UAF bugs.
There are eight syscall functions suffer from UAF bugs, include
ax25_bind(), ax25_release(), ax25_connect(), ax25_ioctl(),
ax25_getname(), ax25_sendmsg(), ax25_getsockopt() and
ax25_info_show().

One of the concurrency UAF can be shown as below:

(USE) | (FREE)
| ax25_device_event
| ax25_dev_device_down
ax25_bind | ...
... | kfree(ax25_dev)
ax25_fillin_cb() | ...
ax25_fillin_cb_from_dev() |
... |

The root cause of UAF bugs is that kfree(ax25_dev) in
ax25_dev_device_down() is not protected by any locks.
When ax25_dev, which there are still pointers point to,
is released, the concurrency UAF bug will happen.

This patch introduces refcount into ax25_dev in order to
guarantee that there are no pointers point to it when ax25_dev
is released.

Signed-off-by: Duoming Zhou <duoming@zju.edu.cn>
Signed-off-by: David S. Miller <davem@davemloft.net>
[OP: backport to 4.19: adjusted context]
Signed-off-by: Ovidiu Panait <ovidiu.panait@windriver.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
include/net/ax25.h | 10 ++++++++++
net/ax25/af_ax25.c | 2 ++
net/ax25/ax25_dev.c | 12 ++++++++++--
net/ax25/ax25_route.c | 3 +++
4 files changed, 25 insertions(+), 2 deletions(-)

--- a/include/net/ax25.h
+++ b/include/net/ax25.h
@@ -236,6 +236,7 @@ typedef struct ax25_dev {
#if defined(CONFIG_AX25_DAMA_SLAVE) || defined(CONFIG_AX25_DAMA_MASTER)
ax25_dama_info dama;
#endif
+ refcount_t refcount;
} ax25_dev;

typedef struct ax25_cb {
@@ -290,6 +291,15 @@ static __inline__ void ax25_cb_put(ax25_
}
}

+#define ax25_dev_hold(__ax25_dev) \
+ refcount_inc(&((__ax25_dev)->refcount))
+
+static __inline__ void ax25_dev_put(ax25_dev *ax25_dev)
+{
+ if (refcount_dec_and_test(&ax25_dev->refcount)) {
+ kfree(ax25_dev);
+ }
+}
static inline __be16 ax25_type_trans(struct sk_buff *skb, struct net_device *dev)
{
skb->dev = dev;
--- a/net/ax25/af_ax25.c
+++ b/net/ax25/af_ax25.c
@@ -101,6 +101,7 @@ again:
spin_unlock_bh(&ax25_list_lock);
lock_sock(sk);
s->ax25_dev = NULL;
+ ax25_dev_put(ax25_dev);
release_sock(sk);
ax25_disconnect(s, ENETUNREACH);
spin_lock_bh(&ax25_list_lock);
@@ -449,6 +450,7 @@ static int ax25_ctl_ioctl(const unsigned
}

out_put:
+ ax25_dev_put(ax25_dev);
ax25_cb_put(ax25);
return ret;

--- a/net/ax25/ax25_dev.c
+++ b/net/ax25/ax25_dev.c
@@ -40,6 +40,7 @@ ax25_dev *ax25_addr_ax25dev(ax25_address
for (ax25_dev = ax25_dev_list; ax25_dev != NULL; ax25_dev = ax25_dev->next)
if (ax25cmp(addr, (ax25_address *)ax25_dev->dev->dev_addr) == 0) {
res = ax25_dev;
+ ax25_dev_hold(ax25_dev);
}
spin_unlock_bh(&ax25_dev_lock);

@@ -59,6 +60,7 @@ void ax25_dev_device_up(struct net_devic
return;
}

+ refcount_set(&ax25_dev->refcount, 1);
dev->ax25_ptr = ax25_dev;
ax25_dev->dev = dev;
dev_hold(dev);
@@ -86,6 +88,7 @@ void ax25_dev_device_up(struct net_devic
spin_lock_bh(&ax25_dev_lock);
ax25_dev->next = ax25_dev_list;
ax25_dev_list = ax25_dev;
+ ax25_dev_hold(ax25_dev);
spin_unlock_bh(&ax25_dev_lock);

ax25_register_dev_sysctl(ax25_dev);
@@ -115,20 +118,22 @@ void ax25_dev_device_down(struct net_dev

if ((s = ax25_dev_list) == ax25_dev) {
ax25_dev_list = s->next;
+ ax25_dev_put(ax25_dev);
spin_unlock_bh(&ax25_dev_lock);
dev->ax25_ptr = NULL;
dev_put(dev);
- kfree(ax25_dev);
+ ax25_dev_put(ax25_dev);
return;
}

while (s != NULL && s->next != NULL) {
if (s->next == ax25_dev) {
s->next = ax25_dev->next;
+ ax25_dev_put(ax25_dev);
spin_unlock_bh(&ax25_dev_lock);
dev->ax25_ptr = NULL;
dev_put(dev);
- kfree(ax25_dev);
+ ax25_dev_put(ax25_dev);
return;
}

@@ -136,6 +141,7 @@ void ax25_dev_device_down(struct net_dev
}
spin_unlock_bh(&ax25_dev_lock);
dev->ax25_ptr = NULL;
+ ax25_dev_put(ax25_dev);
}

int ax25_fwd_ioctl(unsigned int cmd, struct ax25_fwd_struct *fwd)
@@ -152,6 +158,7 @@ int ax25_fwd_ioctl(unsigned int cmd, str
if (ax25_dev->forward != NULL)
return -EINVAL;
ax25_dev->forward = fwd_dev->dev;
+ ax25_dev_put(fwd_dev);
break;

case SIOCAX25DELFWD:
@@ -164,6 +171,7 @@ int ax25_fwd_ioctl(unsigned int cmd, str
return -EINVAL;
}

+ ax25_dev_put(ax25_dev);
return 0;
}

--- a/net/ax25/ax25_route.c
+++ b/net/ax25/ax25_route.c
@@ -119,6 +119,7 @@ static int __must_check ax25_rt_add(stru
ax25_rt->dev = ax25_dev->dev;
ax25_rt->digipeat = NULL;
ax25_rt->ip_mode = ' ';
+ ax25_dev_put(ax25_dev);
if (route->digi_count != 0) {
if ((ax25_rt->digipeat = kmalloc(sizeof(ax25_digi), GFP_ATOMIC)) == NULL) {
write_unlock_bh(&ax25_route_lock);
@@ -175,6 +176,7 @@ static int ax25_rt_del(struct ax25_route
}
}
}
+ ax25_dev_put(ax25_dev);
write_unlock_bh(&ax25_route_lock);

return 0;
@@ -217,6 +219,7 @@ static int ax25_rt_opt(struct ax25_route
}

out:
+ ax25_dev_put(ax25_dev);
write_unlock_bh(&ax25_route_lock);
return err;
}