ACK: [SRU X/B/D/E/F] USB: gadget: fix illegal array access in binding with UDC

[Kleber Souza]

On 2020-05-23 00:37, Thadeu Lima de Souza Cascardo wrote:
> From: Kyungtae Kim <kt0755 at gmail.com>
> 
> FuzzUSB (a variant of syzkaller) found an illegal array access
> using an incorrect index while binding a gadget with UDC.
> 
> Reference: https://www.spinics.net/lists/linux-usb/msg194331.html
> 
> This bug occurs when a size variable used for a buffer
> is misused to access its strcpy-ed buffer.
> Given a buffer along with its size variable (taken from user input),
> from which, a new buffer is created using kstrdup().
> Due to the original buffer containing 0 value in the middle,
> the size of the kstrdup-ed buffer becomes smaller than that of the original.
> So accessing the kstrdup-ed buffer with the same size variable
> triggers memory access violation.
> 
> The fix makes sure no zero value in the buffer,
> by comparing the strlen() of the orignal buffer with the size variable,
> so that the access to the kstrdup-ed buffer is safe.
> 
> BUG: KASAN: slab-out-of-bounds in gadget_dev_desc_UDC_store+0x1ba/0x200
> drivers/usb/gadget/configfs.c:266
> Read of size 1 at addr ffff88806a55dd7e by task syz-executor.0/17208
> 
> CPU: 2 PID: 17208 Comm: syz-executor.0 Not tainted 5.6.8 #1
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
> Call Trace:
>  __dump_stack lib/dump_stack.c:77 [inline]
>  dump_stack+0xce/0x128 lib/dump_stack.c:118
>  print_address_description.constprop.4+0x21/0x3c0 mm/kasan/report.c:374
>  __kasan_report+0x131/0x1b0 mm/kasan/report.c:506
>  kasan_report+0x12/0x20 mm/kasan/common.c:641
>  __asan_report_load1_noabort+0x14/0x20 mm/kasan/generic_report.c:132
>  gadget_dev_desc_UDC_store+0x1ba/0x200 drivers/usb/gadget/configfs.c:266
>  flush_write_buffer fs/configfs/file.c:251 [inline]
>  configfs_write_file+0x2f1/0x4c0 fs/configfs/file.c:283
>  __vfs_write+0x85/0x110 fs/read_write.c:494
>  vfs_write+0x1cd/0x510 fs/read_write.c:558
>  ksys_write+0x18a/0x220 fs/read_write.c:611
>  __do_sys_write fs/read_write.c:623 [inline]
>  __se_sys_write fs/read_write.c:620 [inline]
>  __x64_sys_write+0x73/0xb0 fs/read_write.c:620
>  do_syscall_64+0x9e/0x510 arch/x86/entry/common.c:294
>  entry_SYSCALL_64_after_hwframe+0x49/0xbe
> 
> Signed-off-by: Kyungtae Kim <kt0755 at gmail.com>
> Reported-and-tested-by: Kyungtae Kim <kt0755 at gmail.com>
> Cc: Felipe Balbi <balbi at kernel.org>
> Cc: stable <stable at vger.kernel.org>
> Link: https://lore.kernel.org/r/20200510054326.GA19198@pizza01
> Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
> (cherry picked from commit 15753588bcd4bbffae1cca33c8ced5722477fe1f)
> CVE-2020-13143
> Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo at canonical.com>

Clean cherry-pick, good test results:

Acked-by: Kleber Sacilotto de Souza <kleber.souza at canonical.com>

> ---
>  drivers/usb/gadget/configfs.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/usb/gadget/configfs.c b/drivers/usb/gadget/configfs.c
> index ab9ac48a751a..a7709d126b29 100644
> --- a/drivers/usb/gadget/configfs.c
> +++ b/drivers/usb/gadget/configfs.c
> @@ -260,6 +260,9 @@ static ssize_t gadget_dev_desc_UDC_store(struct config_item *item,
>  	char *name;
>  	int ret;
>  
> +	if (strlen(page) < len)
> +		return -EOVERFLOW;
> +
>  	name = kstrdup(page, GFP_KERNEL);
>  	if (!name)
>  		return -ENOMEM;
>