From: Kuniyuki Iwashima <kuniyu@google.com> mainline inclusion from mainline-v7.2-rc1 commit 06b693d2eb6651a63ad85bad8673de3b7d4edd6d category: bugfix bugzilla: https://atomgit.com/src-openeuler/kernel/issues/17956 CVE: CVE-2026-74289 Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i... -------------------------------- syzbot reported use-after-free in nsim_fib4_prepare_event(). [0] The problem is that the following functions call fib_info_hold() / refcount_inc() while dumping fib_info under RCU, which is unsafe. * mlxsw_sp_router_fib4_event() * rocker_router_fib_event() * nsim_fib4_prepare_event() refcount_inc_not_zero() must be used, but it would be too late there. Let's guarantee the lifetime of fib_info in fib_leaf_notify(). Note that IPv6 does not need the corresponding change since fib6_table_dump() holds fib6_table.tb6_lock. [0]: refcount_t: addition on 0; use-after-free. WARNING: lib/refcount.c:25 at refcount_warn_saturate+0x9f/0x110 lib/refcount.c:25, CPU#0: kworker/u8:15/3420 Modules linked in: CPU: 0 UID: 0 PID: 3420 Comm: kworker/u8:15 Not tainted syzkaller #0 PREEMPT_{RT,(full)} Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026 Workqueue: netns cleanup_net RIP: 0010:refcount_warn_saturate+0x9f/0x110 lib/refcount.c:25 Code: eb 66 85 db 74 3e 83 fb 01 75 4c e8 1b f1 22 fd 48 8d 3d 84 cb f1 0a 67 48 0f b9 3a eb 4a e8 08 f1 22 fd 48 8d 3d 81 cb f1 0a <67> 48 0f b9 3a eb 37 e8 f5 f0 22 fd 48 8d 3d 7e cb f1 0a 67 48 0f RSP: 0018:ffffc9000f2c7270 EFLAGS: 00010293 RAX: ffffffff84a18858 RBX: 0000000000000002 RCX: ffff888032ff9ec0 RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffffffff8f9353e0 RBP: 0000000000000000 R08: ffff888032ff9ec0 R09: 0000000000000005 R10: 0000000000000100 R11: 0000000000000004 R12: ffff8880570cc000 R13: dffffc0000000000 R14: ffff88802b40563c R15: ffff8880570cc000 FS: 0000000000000000(0000) GS:ffff888126173000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007fb1f4d5d000 CR3: 000000006072a000 CR4: 00000000003526f0 Call Trace: <TASK> __refcount_add include/linux/refcount.h:-1 [inline] __refcount_inc include/linux/refcount.h:366 [inline] refcount_inc include/linux/refcount.h:383 [inline] fib_info_hold include/net/ip_fib.h:629 [inline] nsim_fib4_prepare_event drivers/net/netdevsim/fib.c:930 [inline] nsim_fib_event_schedule_work drivers/net/netdevsim/fib.c:1000 [inline] nsim_fib_event_nb+0x1055/0x1240 drivers/net/netdevsim/fib.c:1043 call_fib_notifier+0x45/0x80 net/core/fib_notifier.c:25 call_fib_entry_notifier net/ipv4/fib_trie.c:90 [inline] fib_leaf_notify net/ipv4/fib_trie.c:2176 [inline] fib_table_notify net/ipv4/fib_trie.c:2194 [inline] fib_notify+0x36b/0x5e0 net/ipv4/fib_trie.c:2217 fib_net_dump net/core/fib_notifier.c:70 [inline] register_fib_notifier+0x184/0x360 net/core/fib_notifier.c:108 nsim_fib_create+0x85d/0x9f0 drivers/net/netdevsim/fib.c:1596 nsim_dev_reload_create drivers/net/netdevsim/dev.c:1604 [inline] nsim_dev_reload_up+0x374/0x7c0 drivers/net/netdevsim/dev.c:1058 devlink_reload+0x501/0x8d0 net/devlink/dev.c:475 devlink_pernet_pre_exit+0x1ff/0x420 net/devlink/core.c:558 ops_pre_exit_list net/core/net_namespace.c:161 [inline] ops_undo_list+0x187/0x940 net/core/net_namespace.c:234 cleanup_net+0x56e/0x800 net/core/net_namespace.c:702 process_one_work kernel/workqueue.c:3314 [inline] process_scheduled_works+0xb5d/0x1860 kernel/workqueue.c:3397 worker_thread+0xa53/0xfc0 kernel/workqueue.c:3478 kthread+0x388/0x470 kernel/kthread.c:436 ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245 </TASK> Fixes: 0ae3eb7b4611 ("netdevsim: fib: Perform the route programming in a non-atomic context") Fixes: c3852ef7f2f8 ("ipv4: fib: Replay events when registering FIB notifier") Reported-by: syzbot+cb2aa2390ac024e25f5c@syzkaller.appspotmail.com Closes: https://lore.kernel.org/netdev/6a290011.39669fcc.33b062.00b1.GAE@google.com/ Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com> Reviewed-by: Ido Schimmel <idosch@nvidia.com> Reviewed-by: David Ahern <dsahern@kernel.org> Link: https://patch.msgid.link/20260610061744.2030996-2-kuniyu@google.com Signed-off-by: Jakub Kicinski <kuba@kernel.org> Conflicts: net/ipv4/fib_trie.c [Context differences are due to the following patches not being merged: net: fib_notifier per-netns / error / extack rework: 7c550daffe22 ("net: fib_notifier: make FIB notifier per-netns") 55c894f762a1 ("net: fib_notifier: propagate possible error during fib notifier registration") b7a595577ef3 ("net: fib_notifier: propagate extack down to the notifier block callback") route replay dedup and ADD->REPLACE conversion: 20d1565203e6 ("ipv4: Only Replay routes of interest to new listeners") 446f739104f4 ("ipv4: Remove old route notifications and convert listeners")] Signed-off-by: JiangJieHua <jiangjiehua1@huawei.com> --- include/net/ip_fib.h | 5 +++++ net/ipv4/fib_trie.c | 4 ++++ 2 files changed, 9 insertions(+) diff --git a/include/net/ip_fib.h b/include/net/ip_fib.h index 95eed32d8c6bb..1ba7d0c878145 100644 --- a/include/net/ip_fib.h +++ b/include/net/ip_fib.h @@ -431,6 +431,11 @@ static inline void fib_info_hold(struct fib_info *fi) refcount_inc(&fi->fib_clntref); } +static inline bool fib_info_hold_safe(struct fib_info *fi) +{ + return refcount_inc_not_zero(&fi->fib_clntref); +} + static inline void fib_info_put(struct fib_info *fi) { if (refcount_dec_and_test(&fi->fib_clntref)) diff --git a/net/ipv4/fib_trie.c b/net/ipv4/fib_trie.c index 48d7125501b4e..592a8c7f69366 100644 --- a/net/ipv4/fib_trie.c +++ b/net/ipv4/fib_trie.c @@ -1959,8 +1959,12 @@ static void fib_leaf_notify(struct net *net, struct key_vector *l, if (tb->tb_id != fa->tb_id) continue; + if (!fib_info_hold_safe(fa->fa_info)) + continue; + call_fib_entry_notifier(nb, net, FIB_EVENT_ENTRY_ADD, l->key, KEYLENGTH - fa->fa_slen, fa); + fib_info_put(fa->fa_info); } } -- 2.33.8