Merge: CVE-2025-21857: net/sched: cls_api: fix error handling causing NULL dereference

MR: https://gitlab.com/redhat/centos-stream/src/kernel/centos-stream-10/-/merge_requests/578

JIRA: https://issues.redhat.com/browse/RHEL-83372
CVE: CVE-2025-21857

```
commit 071ed42
Author: Pierre Riteau <pierre@stackhpc.com>
Date:   Thu Feb 13 23:36:10 2025 +0100

    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]

    Fixes: 80cd22c ("net/sched: cls_api: Support hardware miss to tc action")
    Signed-off-by: Pierre Riteau <pierre@stackhpc.com>
    Reviewed-by: Michal Swiatkowski <michal.swiatkowski@linux.intel.com>
    Link: https://patch.msgid.link/20250213223610.320278-1-pierre@stackhpc.com
    Signed-off-by: Jakub Kicinski <kuba@kernel.org>```

Signed-off-by: CKI Backport Bot <cki-ci-bot+cki-gitlab-backport-bot@redhat.com>

---

<small>Created 2025-03-13 07:56 UTC by backporter - [KWF FAQ](https://red.ht/kernel_workflow_doc) - [Slack #team-kernel-workflow](https://redhat-internal.slack.com/archives/C04LRUPMJQ5) - [Source](https://gitlab.com/cki-project/kernel-workflow/-/blob/main/webhook/utils/backporter.py) - [Documentation](https://gitlab.com/cki-project/kernel-workflow/-/blob/main/docs/README.backporter.md) - [Report an issue](https://gitlab.com/cki-project/kernel-workflow/-/issues/new?issue%5Btitle%5D=backporter%20webhook%20issue)</small>

Approved-by: Xin Long <lxin@redhat.com>
Approved-by: Antoine Tenart <atenart@redhat.com>
Approved-by: CKI KWF Bot <cki-ci-bot+kwf-gitlab-com@redhat.com>

Merged-by: Julio Faracco <jfaracco@redhat.com>

Author: jcfaracco

net/sched/cls_api.c

@@ -97,7 +97,7 @@ tcf_exts_miss_cookie_base_alloc(struct tcf_exts *exts, struct tcf_proto *tp,
 
 	err = xa_alloc_cyclic(&tcf_exts_miss_cookies_xa, &n->miss_cookie_base,
 			      n, xa_limit_32b, &next, GFP_KERNEL);
-	if (err)
+	if (err < 0)
 		goto err_xa_alloc;
 
 	exts->miss_cookie_node = n;