Re: [PATCH] HID: i2c-hid: fix OOB write in i2c_hid_set_or_send_report()

[Benjamin Tissoires <benjamin.tissoires@redhat.com>]

On Mar 14 2016 or thereabouts, Dmitry Torokhov wrote:
> From: Dmitry Torokhov <dtor@chromium.org>
> 
> Even though hid_hw_* checks that passed in data_len is less than
> HID_MAX_BUFFER_SIZE it is not enough, as i2c-hid does not necessarily
> allocate buffers of HID_MAX_BUFFER_SIZE but rather checks all device
> reports and select largest size. In-kernel users normally just send as much
> data as report needs, so there is no problem, but hidraw users can do
> whatever they please:
> 
> BUG: KASAN: slab-out-of-bounds in memcpy+0x34/0x54 at addr ffffffc07135ea80
> Write of size 4101 by task syz-executor/8747
> CPU: 2 PID: 8747 Comm: syz-executor Tainted: G    BU         3.18.0 #37
> Hardware name: Google Tegra210 Smaug Rev 1,3+ (DT)
> Call trace:
> [<ffffffc00020ebcc>] dump_backtrace+0x0/0x258 arch/arm64/kernel/traps.c:83
> [<ffffffc00020ee40>] show_stack+0x1c/0x2c arch/arm64/kernel/traps.c:172
> [<     inline     >] __dump_stack lib/dump_stack.c:15
> [<ffffffc001958114>] dump_stack+0x90/0x140 lib/dump_stack.c:50
> [<     inline     >] print_error_description mm/kasan/report.c:97
> [<     inline     >] kasan_report_error mm/kasan/report.c:278
> [<ffffffc0004597dc>] kasan_report+0x268/0x530 mm/kasan/report.c:305
> [<ffffffc0004592e8>] __asan_storeN+0x20/0x150 mm/kasan/kasan.c:718
> [<ffffffc0004594e0>] memcpy+0x30/0x54 mm/kasan/kasan.c:299
> [<ffffffc001306354>] __i2c_hid_command+0x2b0/0x7b4 drivers/hid/i2c-hid/i2c-hid.c:178
> [<     inline     >] i2c_hid_set_or_send_report drivers/hid/i2c-hid/i2c-hid.c:321
> [<ffffffc0013079a0>] i2c_hid_output_raw_report.isra.2+0x3d4/0x4b8 drivers/hid/i2c-hid/i2c-hid.c:589
> [<ffffffc001307ad8>] i2c_hid_output_report+0x54/0x68 drivers/hid/i2c-hid/i2c-hid.c:602
> [<     inline     >] hid_hw_output_report include/linux/hid.h:1039
> [<ffffffc0012cc7a0>] hidraw_send_report+0x400/0x414 drivers/hid/hidraw.c:154
> [<ffffffc0012cc7f4>] hidraw_write+0x40/0x64 drivers/hid/hidraw.c:177
> [<ffffffc0004681dc>] vfs_write+0x1d4/0x3cc fs/read_write.c:534
> [<     inline     >] SYSC_pwrite64 fs/read_write.c:627
> [<ffffffc000468984>] SyS_pwrite64+0xec/0x144 fs/read_write.c:614
> Object at ffffffc07135ea80, in cache kmalloc-512
> Object allocated with size 268 bytes.
> 
> Let's check data length against the buffer size before attempting to copy
> data over.
> 
> Reported-by: Alexander Potapenko <glider@google.com>
> Signed-off-by: Dmitry Torokhov <dtor@chromium.org>
> ---
> 
> This should probably go to stable as well, leaving it to Jiri/Benjamin
> to decide.

Works for me:
Reviewed-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>

I also think this should go to stable. Jiri, can you add the tag when
committing?

Cheers,
Benjamin

> 
> 
>  drivers/hid/i2c-hid/i2c-hid.c | 16 ++++++++++------
>  1 file changed, 10 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/hid/i2c-hid/i2c-hid.c b/drivers/hid/i2c-hid/i2c-hid.c
> index b921693..bb89749 100644
> --- a/drivers/hid/i2c-hid/i2c-hid.c
> +++ b/drivers/hid/i2c-hid/i2c-hid.c
> @@ -283,17 +283,21 @@ static int i2c_hid_set_or_send_report(struct i2c_client *client, u8 reportType,
>  	u16 dataRegister = le16_to_cpu(ihid->hdesc.wDataRegister);
>  	u16 outputRegister = le16_to_cpu(ihid->hdesc.wOutputRegister);
>  	u16 maxOutputLength = le16_to_cpu(ihid->hdesc.wMaxOutputLength);
> +	u16 size;
> +	int args_len;
> +	int index = 0;
> +
> +	i2c_hid_dbg(ihid, "%s\n", __func__);
> +
> +	if (data_len > ihid->bufsize)
> +		return -EINVAL;
>  
> -	/* hid_hw_* already checked that data_len < HID_MAX_BUFFER_SIZE */
> -	u16 size =	2			/* size */ +
> +	size =		2			/* size */ +
>  			(reportID ? 1 : 0)	/* reportID */ +
>  			data_len		/* buf */;
> -	int args_len =	(reportID >= 0x0F ? 1 : 0) /* optional third byte */ +
> +	args_len =	(reportID >= 0x0F ? 1 : 0) /* optional third byte */ +
>  			2			/* dataRegister */ +
>  			size			/* args */;
> -	int index = 0;
> -
> -	i2c_hid_dbg(ihid, "%s\n", __func__);
>  
>  	if (!use_data && maxOutputLength == 0)
>  		return -ENOSYS;
> -- 
> 2.7.0.rc3.207.g0ac5344
> 
> 
> -- 
> Dmitry