Re: [PATCH net] tty: Fix uninit-value access in ppp_sync_receive()

On Thu, Nov 09, 2023 at 12:44:20AM +0900, Shigeru Yoshida wrote:
> KMSAN reported the following uninit-value access issue:
> 
> =====================================================
> BUG: KMSAN: uninit-value in ppp_sync_input drivers/net/ppp/ppp_synctty.c:690 [inline]
> BUG: KMSAN: uninit-value in ppp_sync_receive+0xdc9/0xe70 drivers/net/ppp/ppp_synctty.c:334
>  ppp_sync_input drivers/net/ppp/ppp_synctty.c:690 [inline]
>  ppp_sync_receive+0xdc9/0xe70 drivers/net/ppp/ppp_synctty.c:334
>  tiocsti+0x328/0x450 drivers/tty/tty_io.c:2295
>  tty_ioctl+0x808/0x1920 drivers/tty/tty_io.c:2694
>  vfs_ioctl fs/ioctl.c:51 [inline]
>  __do_sys_ioctl fs/ioctl.c:871 [inline]
>  __se_sys_ioctl+0x211/0x400 fs/ioctl.c:857
>  __x64_sys_ioctl+0x97/0xe0 fs/ioctl.c:857
>  do_syscall_x64 arch/x86/entry/common.c:51 [inline]
>  do_syscall_64+0x44/0x110 arch/x86/entry/common.c:82
>  entry_SYSCALL_64_after_hwframe+0x63/0x6b
> 
> Uninit was created at:
>  __alloc_pages+0x75d/0xe80 mm/page_alloc.c:4591
>  __alloc_pages_node include/linux/gfp.h:238 [inline]
>  alloc_pages_node include/linux/gfp.h:261 [inline]
>  __page_frag_cache_refill+0x9a/0x2c0 mm/page_alloc.c:4691
>  page_frag_alloc_align+0x91/0x5d0 mm/page_alloc.c:4722
>  page_frag_alloc include/linux/gfp.h:322 [inline]
>  __netdev_alloc_skb+0x215/0x6d0 net/core/skbuff.c:728
>  netdev_alloc_skb include/linux/skbuff.h:3225 [inline]
>  dev_alloc_skb include/linux/skbuff.h:3238 [inline]
>  ppp_sync_input drivers/net/ppp/ppp_synctty.c:669 [inline]
>  ppp_sync_receive+0x237/0xe70 drivers/net/ppp/ppp_synctty.c:334
>  tiocsti+0x328/0x450 drivers/tty/tty_io.c:2295
>  tty_ioctl+0x808/0x1920 drivers/tty/tty_io.c:2694
>  vfs_ioctl fs/ioctl.c:51 [inline]
>  __do_sys_ioctl fs/ioctl.c:871 [inline]
>  __se_sys_ioctl+0x211/0x400 fs/ioctl.c:857
>  __x64_sys_ioctl+0x97/0xe0 fs/ioctl.c:857
>  do_syscall_x64 arch/x86/entry/common.c:51 [inline]
>  do_syscall_64+0x44/0x110 arch/x86/entry/common.c:82
>  entry_SYSCALL_64_after_hwframe+0x63/0x6b
> 
> CPU: 0 PID: 12950 Comm: syz-executor.1 Not tainted 6.6.0-14500-g1c41041124bd #10
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.2-1.fc38 04/01/2014
> =====================================================
> 
> ppp_sync_input() checks the first 2 bytes of the data are PPP_ALLSTATIONS
> and PPP_UI. However, if the data length is 1 and the first byte is
> PPP_ALLSTATIONS, an access to an uninitialized value occurs when checking
> PPP_UI. This patch resolves this issue by checking the data length.
> 
> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> Signed-off-by: Shigeru Yoshida <[email protected]>

Reviewed-by: Simon Horman <[email protected]>