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

CKI Backport Botrequested to merge
redhat/red-hat-ci-tools/kernel/bot-branches/centos-stream/src/kernel/centos-stream-10:backport-RHEL-83372-centos-stream-10-main into main

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

commit 071ed42cff4fcdd89025d966d48eabef59913bf2
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: 80cd22c35c90 ("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>

---

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