Re: [PATCH] can: bcm: Fix UAF in bcm_proc_show()

[Oliver Hartkopp]

Hello YueHaibing,

thanks for the patch!

Indeed the proc entry can be removed as first action after lock_sock(). 
Good catch!

On 2023-07-15 11:25, YueHaibing wrote:
> BUG: KASAN: slab-use-after-free in bcm_proc_show+0x969/0xa80
> Read of size 8 at addr ffff888155846230 by task cat/7862
>
> CPU: 1 PID: 7862 Comm: cat Not tainted 6.5.0-rc1-00153-gc8746099c197 #230
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014
> Call Trace:
>   <TASK>
>   dump_stack_lvl+0xd5/0x150
>   print_report+0xc1/0x5e0
>   kasan_report+0xba/0xf0
>   bcm_proc_show+0x969/0xa80
>   seq_read_iter+0x4f6/0x1260
>   seq_read+0x165/0x210
>   proc_reg_read+0x227/0x300
>   vfs_read+0x1d5/0x8d0
>   ksys_read+0x11e/0x240
>   do_syscall_64+0x35/0xb0
>   entry_SYSCALL_64_after_hwframe+0x63/0xcd
>
> Allocated by task 7846:
>   kasan_save_stack+0x1e/0x40
>   kasan_set_track+0x21/0x30
>   __kasan_kmalloc+0x9e/0xa0
>   bcm_sendmsg+0x264b/0x44e0
>   sock_sendmsg+0xda/0x180
>   ____sys_sendmsg+0x735/0x920
>   ___sys_sendmsg+0x11d/0x1b0
>   __sys_sendmsg+0xfa/0x1d0
>   do_syscall_64+0x35/0xb0
>   entry_SYSCALL_64_after_hwframe+0x63/0xcd
>
> Freed by task 7846:
>   kasan_save_stack+0x1e/0x40
>   kasan_set_track+0x21/0x30
>   kasan_save_free_info+0x27/0x40
>   ____kasan_slab_free+0x161/0x1c0
>   slab_free_freelist_hook+0x119/0x220
>   __kmem_cache_free+0xb4/0x2e0
>   rcu_core+0x809/0x1bd0
>
> bcm_op is freed before procfs entry be removed in bcm_release(),
> this lead to bcm_proc_show() may read the freed bcm_op.
>
> Fixes: ffd980f976e7 ("[CAN]: Add broadcast manager (bcm) protocol")
> Signed-off-by: YueHaibing <yuehaibing@xxxxxxxxxx>

Reviewed-by: Oliver Hartkopp <socketcan@xxxxxxxxxxxx>
Acked-by: Oliver Hartkopp <socketcan@xxxxxxxxxxxx>

Many thanks!

Oliver

> ---
>   net/can/bcm.c | 12 ++++++------
>   1 file changed, 6 insertions(+), 6 deletions(-)
>
> diff --git a/net/can/bcm.c b/net/can/bcm.c
> index 9ba35685b043..9168114fc87f 100644
> --- a/net/can/bcm.c
> +++ b/net/can/bcm.c
> @@ -1526,6 +1526,12 @@ static int bcm_release(struct socket *sock)
>   
>   	lock_sock(sk);
>   
> +#if IS_ENABLED(CONFIG_PROC_FS)
> +	/* remove procfs entry */
> +	if (net->can.bcmproc_dir && bo->bcm_proc_read)
> +		remove_proc_entry(bo->procname, net->can.bcmproc_dir);
> +#endif /* CONFIG_PROC_FS */
> +
>   	list_for_each_entry_safe(op, next, &bo->tx_ops, list)
>   		bcm_remove_op(op);
>   
> @@ -1561,12 +1567,6 @@ static int bcm_release(struct socket *sock)
>   	list_for_each_entry_safe(op, next, &bo->rx_ops, list)
>   		bcm_remove_op(op);
>   
> -#if IS_ENABLED(CONFIG_PROC_FS)
> -	/* remove procfs entry */
> -	if (net->can.bcmproc_dir && bo->bcm_proc_read)
> -		remove_proc_entry(bo->procname, net->can.bcmproc_dir);
> -#endif /* CONFIG_PROC_FS */
> -
>   	/* remove device reference */
>   	if (bo->bound) {
>   		bo->bound   = 0;