Subject: Re: [PATCH net v4 3/3] net: sched: use RCU read-side critical section in taprio_dump()

From: Simon Horman <[email-masked]>
Date: Wed, 4 Sep 2024 11:17:38 +0100

On Tue, Sep 03, 2024 at 05:07:08PM +0300, Dmitry Antipov wrote:
> Fix possible use-after-free in 'taprio_dump()' by adding RCU
> read-side critical section there. Never seen on x86 but
> found on a KASAN-enabled arm64 system when investigating
> https://syzkaller.appspot.com/bug?extid=b65e0af58423fc8a73aa:
> 
> [T15862] BUG: KASAN: slab-use-after-free in taprio_dump+0xa0c/0xbb0
> [T15862] Read of size 4 at addr ffff0000d4bb88f8 by task repro/15862
> [T15862]
> [T15862] CPU: 0 UID: 0 PID: 15862 Comm: repro Not tainted 6.11.0-rc1-00293-gdefaf1a2113a-dirty #2
> [T15862] Hardware name: QEMU QEMU Virtual Machine, BIOS edk2-20240524-5.fc40 05/24/2024
> [T15862] Call trace:
> [T15862]  dump_backtrace+0x20c/0x220
> [T15862]  show_stack+0x2c/0x40
> [T15862]  dump_stack_lvl+0xf8/0x174
> [T15862]  print_report+0x170/0x4d8
> [T15862]  kasan_report+0xb8/0x1d4
> [T15862]  __asan_report_load4_noabort+0x20/0x2c
> [T15862]  taprio_dump+0xa0c/0xbb0
> [T15862]  tc_fill_qdisc+0x540/0x1020
> [T15862]  qdisc_notify.isra.0+0x330/0x3a0
> [T15862]  tc_modify_qdisc+0x7b8/0x1838
> [T15862]  rtnetlink_rcv_msg+0x3c8/0xc20
> [T15862]  netlink_rcv_skb+0x1f8/0x3d4
> [T15862]  rtnetlink_rcv+0x28/0x40
> [T15862]  netlink_unicast+0x51c/0x790
> [T15862]  netlink_sendmsg+0x79c/0xc20
> [T15862]  __sock_sendmsg+0xe0/0x1a0
> [T15862]  ____sys_sendmsg+0x6c0/0x840
> [T15862]  ___sys_sendmsg+0x1ac/0x1f0
> [T15862]  __sys_sendmsg+0x110/0x1d0
> [T15862]  __arm64_sys_sendmsg+0x74/0xb0
> [T15862]  invoke_syscall+0x88/0x2e0
> [T15862]  el0_svc_common.constprop.0+0xe4/0x2a0
> [T15862]  do_el0_svc+0x44/0x60
> [T15862]  el0_svc+0x50/0x184
> [T15862]  el0t_64_sync_handler+0x120/0x12c
> [T15862]  el0t_64_sync+0x190/0x194
> [T15862]
> [T15862] Allocated by task 15857:
> [T15862]  kasan_save_stack+0x3c/0x70
> [T15862]  kasan_save_track+0x20/0x3c
> [T15862]  kasan_save_alloc_info+0x40/0x60
> [T15862]  __kasan_kmalloc+0xd4/0xe0
> [T15862]  __kmalloc_cache_noprof+0x194/0x334
> [T15862]  taprio_change+0x45c/0x2fe0
> [T15862]  tc_modify_qdisc+0x6a8/0x1838
> [T15862]  rtnetlink_rcv_msg+0x3c8/0xc20
> [T15862]  netlink_rcv_skb+0x1f8/0x3d4
> [T15862]  rtnetlink_rcv+0x28/0x40
> [T15862]  netlink_unicast+0x51c/0x790
> [T15862]  netlink_sendmsg+0x79c/0xc20
> [T15862]  __sock_sendmsg+0xe0/0x1a0
> [T15862]  ____sys_sendmsg+0x6c0/0x840
> [T15862]  ___sys_sendmsg+0x1ac/0x1f0
> [T15862]  __sys_sendmsg+0x110/0x1d0
> [T15862]  __arm64_sys_sendmsg+0x74/0xb0
> [T15862]  invoke_syscall+0x88/0x2e0
> [T15862]  el0_svc_common.constprop.0+0xe4/0x2a0
> [T15862]  do_el0_svc+0x44/0x60
> [T15862]  el0_svc+0x50/0x184
> [T15862]  el0t_64_sync_handler+0x120/0x12c
> [T15862]  el0t_64_sync+0x190/0x194
> [T15862]
> [T15862] Freed by task 6192:
> [T15862]  kasan_save_stack+0x3c/0x70
> [T15862]  kasan_save_track+0x20/0x3c
> [T15862]  kasan_save_free_info+0x4c/0x80
> [T15862]  poison_slab_object+0x110/0x160
> [T15862]  __kasan_slab_free+0x3c/0x74
> [T15862]  kfree+0x134/0x3c0
> [T15862]  taprio_free_sched_cb+0x18c/0x220
> [T15862]  rcu_core+0x920/0x1b7c
> [T15862]  rcu_core_si+0x10/0x1c
> [T15862]  handle_softirqs+0x2e8/0xd64
> [T15862]  __do_softirq+0x14/0x20
> 

Hi Dmitry,

As a fix for net, there should be a Fixes tag here,
indicating the first commit in which this bug manifested.
This can be the first commit in the tree, if the
bug has been there since then.

If the patch-set is not going to be resent, it is probably
sufficient to just reply with one here. And it may be a good
idea to do so regardless.

> Signed-off-by: Dmitry Antipov <[email-masked]>