Re: [PATCH 3/3] IB/srpt: Fix a use-after-free

[Greg KH <gregkh@linuxfoundation.org>]

On Tue, Jul 10, 2018 at 10:32:00AM -0700, Bart Van Assche wrote:
> Make sure that channel objects continue to exist until the target
> core has called the .close_session() callback function. This patch
> voids that KASAN sporadically reports the following:
> 
> BUG: KASAN: use-after-free in do_raw_spin_lock+0x1c/0x130
> Read of size 4 at addr ffff8801534b16e4 by task rmdir/14805
> CPU: 16 PID: 14805 Comm: rmdir Not tainted 4.18.0-rc2-dbg+ #5
> Call Trace:
> dump_stack+0xa4/0xf5
> print_address_description+0x6f/0x270
> kasan_report+0x241/0x360
> __asan_load4+0x78/0x80
> do_raw_spin_lock+0x1c/0x130
> _raw_spin_lock_irqsave+0x52/0x60
> srpt_set_ch_state+0x27/0x70 [ib_srpt]
> srpt_disconnect_ch+0x1b/0xc0 [ib_srpt]
> srpt_close_session+0xa8/0x260 [ib_srpt]
> target_shutdown_sessions+0x170/0x180 [target_core_mod]
> core_tpg_del_initiator_node_acl+0xf3/0x200 [target_core_mod]
> target_fabric_nacl_base_release+0x25/0x30 [target_core_mod]
> config_item_release+0x9c/0x110 [configfs]
> config_item_put+0x26/0x30 [configfs]
> configfs_rmdir+0x3b8/0x510 [configfs]
> vfs_rmdir+0xb3/0x1e0
> do_rmdir+0x262/0x2c0
> do_syscall_64+0x77/0x230
> entry_SYSCALL_64_after_hwframe+0x49/0xbe
> 
> Fixes: a42d985bd5b2 ("ib_srpt: Initial SRP Target merge for v3.3-rc1")
> Signed-off-by: Bart Van Assche <bart.vanassche@wdc.com>
> Cc: <stable@vger.kernel.org>
> ---
>  drivers/infiniband/ulp/srpt/ib_srpt.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/infiniband/ulp/srpt/ib_srpt.c b/drivers/infiniband/ulp/srpt/ib_srpt.c
> index 325bae29e90d..705f6a992d82 100644
> --- a/drivers/infiniband/ulp/srpt/ib_srpt.c
> +++ b/drivers/infiniband/ulp/srpt/ib_srpt.c
> @@ -2152,6 +2152,7 @@ static int srpt_cm_req_recv(struct srpt_device *const sdev,
>  	}
>  
>  	kref_init(&ch->kref);
> +	kref_get(&ch->kref);

kref_init starts the reference count at at 1, so why do you need to
increment it right away?  That feels like something is "odd" here, why
do you start with 2 references in the same function?

thanks,

greg k-h