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

[Stav Aviram]

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")
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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