"value":"In the Linux kernel, the following vulnerability has been resolved:\n\nax25: Fix refcount imbalance on inbound connections\n\nWhen releasing a socket in ax25_release(), we call netdev_put() to\ndecrease the refcount on the associated ax.25 device. However, the\nexecution path for accepting an incoming connection never calls\nnetdev_hold(). This imbalance leads to refcount errors, and ultimately\nto kernel crashes.\n\nA typical call trace for the above situation will start with one of the\nfollowing errors:\n\n refcount_t: decrement hit 0; leaking memory.\n refcount_t: underflow; use-after-free.\n\nAnd will then have a trace like:\n\n Call Trace:\n <TASK>\n ? show_regs+0x64/0x70\n ? __warn+0x83/0x120\n ? refcount_warn_saturate+0xb2/0x100\n ? report_bug+0x158/0x190\n ? prb_read_valid+0x20/0x30\n ? handle_bug+0x3e/0x70\n ? exc_invalid_op+0x1c/0x70\n ? asm_exc_invalid_op+0x1f/0x30\n ? refcount_warn_saturate+0xb2/0x100\n ? refcount_warn_saturate+0xb2/0x100\n ax25_release+0x2ad/0x360\n __sock_release+0x35/0xa0\n sock_close+0x19/0x20\n [...]\n\nOn reboot (or any attempt to remove the interface), the kernel gets\nstuck in an infinite loop:\n\n unregister_netdevice: waiting for ax0 to become free. Usage count = 0\n\nThis patch corrects these issues by ensuring that we call netdev_hold()\nand ax25_dev_hold() for new connections in ax25_accept(). This makes the\nlogic leading to ax25_accept() match the logic for ax25_bind(): in both\ncases we increment the refcount, which is ultimately decremented in\nax25_release()."
