net/sched: cls_api: fix error handling causing NULL dereference

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

net/sched: cls_api: fix error handling causing NULL dereference

tcf_exts_miss_cookie_base_alloc() calls xa_alloc_cyclic() which can

return 1 if the allocation succeeded after wrapping. This was treated as

an error, with value 1 returned to caller tcf_exts_init_ex() which sets

exts->actions to NULL and returns 1 to caller fl_change().

fl_change() treats err == 1 as success, calling tcf_exts_validate_ex()

which calls tcf_action_init() with exts->actions as argument, where it

is dereferenced.

Example trace:

BUG: kernel NULL pointer dereference, address: 0000000000000000

CPU: 114 PID: 16151 Comm: handler114 Kdump: loaded Not tainted 5.14.0-503.16.1.el9_5.x86_64 #1

RIP: 0010:tcf_action_init+0x1f8/0x2c0

Call Trace:

tcf_action_init+0x1f8/0x2c0

tcf_exts_validate_ex+0x175/0x190

fl_change+0x537/0x1120 [cls_flower]