In the Linux kernel, the following vulnerability has been resolved: nexthop: initialize extack in nh_res_bucket_migrate() nh_res_bucket_mi

In the Linux kernel, the following vulnerability has been resolved:

nexthop: initialize extack in nh_res_bucket_migrate()

nh_res_bucket_migrate() passes an uninitialized netlink_ext_ack to
call_nexthop_res_bucket_notifiers(). When
nh_notifier_res_bucket_info_init() fails (e.g. the kzalloc returns
-ENOMEM), the error is propagated back before any notifier sets
extack._msg, and the error path formats the stale pointer with
pr_err_ratelimited("%s\n", extack._msg). With CONFIG_INIT_STACK_NONE
this dereferences uninitialized stack memory:

Oops: general protection fault, probably for non-canonical address ...
KASAN: maybe wild-memory-access in range [...]
RIP: 0010:string (lib/vsprintf.c:730)
vsnprintf (lib/vsprintf.c:2945)
_printk (kernel/printk/printk.c:2504)
nh_res_bucket_migrate (net/ipv4/nexthop.c:1816)
nh_res_table_upkeep (net/ipv4/nexthop.c:1866)
rtm_new_nexthop (net/ipv4/nexthop.c:3323)
rtnetlink_rcv_msg (net/core/rtnetlink.c:7076)
netlink_sendmsg (net/netlink/af_netlink.c:1900)
Kernel panic - not syncing: Fatal exception

Zero-initialize extack so _msg is NULL on error paths that never set it.