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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
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;