NACK/Cmnt: [SRU][J][PATCH v1 1/1] net/sched: cls_api: fix error handling causing NULL dereference

[Chia-Lin Kao (AceLan)]

On Thu, Jun 19, 2025 at 05:38:59PM +0000, Stav Aviram wrote:
> From 0ae08f477df8fea6078bd5ba581d19f44973ba9c Mon Sep 17 00:00:00 2001
> Message-Id: <0ae08f477df8fea6078bd5ba581d19f44973ba9c.1750344948.git.saviram at nvidia.com>
> In-Reply-To: <cover.1750344948.git.saviram at nvidia.com>
> References: <cover.1750344948.git.saviram at nvidia.com>
> From: Pierre Riteau <pierre at stackhpc.com>
> Date: Thu, 13 Feb 2025 23:36:10 +0100
> To: kernel-team at lists.ubuntu.com
> Subject: [SRU][J][PATCH v1 1/1] net/sched: cls_api: fix error handling causing NULL
>  dereference
> 
> BugLink: https://bugs.launchpad.net/bugs/2114965
> 
> 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")
Jammy, 5.15 kernel, doesn't include this commit, so doesn't need this patch.

> Signed-off-by: Pierre Riteau <pierre at stackhpc.com>
> Reviewed-by: Michal Swiatkowski <michal.swiatkowski at linux.intel.com>
> Link: https://patch.msgid.link/20250213223610.320278-1-pierre@stackhpc.com
> Signed-off-by: Jakub Kicinski <kuba at kernel.org>
> (cherry picked from commit 071ed42cff4fcdd89025d966d48eabef59913bf2)
> Signed-off-by: Stav Aviram <saviram at nvidia.com>
> ---
>  net/sched/cls_api.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/net/sched/cls_api.c b/net/sched/cls_api.c
> index 1296b1196e56..17792a270e8c 100644
> --- a/net/sched/cls_api.c
> +++ b/net/sched/cls_api.c
> @@ -96,7 +96,7 @@ 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;
> --
> 2.34.1

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