ax25: Fix reference count leak issues of ax25_dev

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: ax25: Fix reference count leak issues of ax25_dev The ax25_addr_ax25dev() and ax25_dev_device_down() exist a reference count leak issue of the object "ax25_dev". Memory leak issue in ax25_addr_ax25dev(): The reference count of the object "ax25_dev" can be increased multiple times in ax25_addr_ax25dev(). This will cause a memory leak. Memory leak issues in ax25_dev_device_down(): The reference count of ax25_dev is set to 1 in ax25_dev_device_up() and then increase the reference count when ax25_dev is added to ax25_dev_list. As a result, the reference count of ax25_dev is 2. But when the device is shutting down. The ax25_dev_device_down() drops the reference count once or twice depending on if we goto unlock_put or not, which will cause memory leak. As for the issue of ax25_addr_ax25dev(), it is impossible for one pointer to be on a list twice. So add a break in ax25_addr_ax25dev(). As for the issue of ax25_dev_device_down(), increase the reference count of ax25_dev once in ax25_dev_device_up() and decrease the reference count of ax25_dev after it is removed from the ax25_dev_list.

References

• https://git.kernel.org/stable/c/ae467750a3765dd1092eb29f58247950a2f9b60c
• https://git.kernel.org/stable/c/38eb01edfdaa1562fa00429be2e33f45383b1b3a
• https://git.kernel.org/stable/c/81d8240b0a243b3ddd8fa8aa172f1acc2f7cc8f3
• https://git.kernel.org/stable/c/1ea02699c7557eeb35ccff2bd822de1b3e09d868
• https://git.kernel.org/stable/c/b505e0319852b08a3a716b64620168eab21f4ced