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ax25: add refcount in ax25_dev to avoid UAF bugs

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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>
This commit is contained in:
Duoming Zhou 2022-01-28 12:47:16 +08:00 committed by David S. Miller
parent 4e0f718daf
commit d01ffb9eee
4 changed files with 25 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

10
include/net/ax25.h
View File

@ -239,6 +239,7 @@ 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 {
@ -293,6 +294,15 @@ static __inline__ void ax25_cb_put(ax25_cb *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;

2
net/ax25/af_ax25.c
View File

@ -91,6 +91,7 @@ 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);
@ -439,6 +440,7 @@ static int ax25_ctl_ioctl(const unsigned int cmd, void __user *arg)
}
out_put:
ax25_dev_put(ax25_dev);
ax25_cb_put(ax25);
return ret;

12
net/ax25/ax25_dev.c
View File

@ -37,6 +37,7 @@ ax25_dev *ax25_addr_ax25dev(ax25_address *addr)
for (ax25_dev = ax25_dev_list; ax25_dev != NULL; ax25_dev = ax25_dev->next)
if (ax25cmp(addr, (const ax25_address *)ax25_dev->dev->dev_addr) == 0) {
res = ax25_dev;
ax25_dev_hold(ax25_dev);
}
spin_unlock_bh(&ax25_dev_lock);
@ -56,6 +57,7 @@ void ax25_dev_device_up(struct net_device *dev)
return;
}
refcount_set(&ax25_dev->refcount, 1);
dev->ax25_ptr = ax25_dev;
ax25_dev->dev = dev;
dev_hold_track(dev, &ax25_dev->dev_tracker, GFP_ATOMIC);
@ -83,6 +85,7 @@ void ax25_dev_device_up(struct net_device *dev)
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);
@ -112,20 +115,22 @@ void ax25_dev_device_down(struct net_device *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_track(dev, &ax25_dev->dev_tracker);
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_track(dev, &ax25_dev->dev_tracker);
kfree(ax25_dev);
ax25_dev_put(ax25_dev);
return;
}
@ -133,6 +138,7 @@ void ax25_dev_device_down(struct net_device *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)
@ -149,6 +155,7 @@ int ax25_fwd_ioctl(unsigned int cmd, struct ax25_fwd_struct *fwd)
if (ax25_dev->forward != NULL)
return -EINVAL;
ax25_dev->forward = fwd_dev->dev;
ax25_dev_put(fwd_dev);
break;
case SIOCAX25DELFWD:
@ -161,6 +168,7 @@ int ax25_fwd_ioctl(unsigned int cmd, struct ax25_fwd_struct *fwd)
return -EINVAL;
}
ax25_dev_put(ax25_dev);
return 0;
}

3
net/ax25/ax25_route.c
View File

@ -116,6 +116,7 @@ static int __must_check ax25_rt_add(struct ax25_routes_struct *route)
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);
@ -172,6 +173,7 @@ static int ax25_rt_del(struct ax25_routes_struct *route)
}
}
}
ax25_dev_put(ax25_dev);
write_unlock_bh(&ax25_route_lock);
return 0;
@ -214,6 +216,7 @@ static int ax25_rt_opt(struct ax25_route_opt_struct *rt_option)
}
out:
ax25_dev_put(ax25_dev);
write_unlock_bh(&ax25_route_lock);
return err;
}