[lvc-project] [PATCH 5.10/6.1] scsi: sg: replace scatter_elem_sz value 0 with PAGE_SIZE

[Fedor Pchelkin]

On Tue, 29. Jul 03:13, Tonofa Boris wrote:
> From: Edward Adam Davis <eadavis at qq.com>

scripts/checkpatch.pl жалуется. Просьба его предварительно прогонять на
патчи, которые отправляете, и, при необходимости, учитывать его замечания.

Либо этот From здесь не нужен, либо нужен соответствующий для него
Signed-off-by в зоне подписей. 

> 
> syzbot reported a shift‑out‑of‑bounds in sg_build_indirect() [1].
> 
> The reproducer writes 0 to /sys/module/sg/parameters/scatter_elem_sz,
> then opens “/dev/sg0”; on the sg_open() path we get:
> 
>     num   = scatter_elem_sz;          /* 0 */
>     order = get_order(num);           /* 52 on x86‑64 */
>     ret_sz = 1 << (PAGE_SHIFT + order);   /* 1 << 64 → UB */
> 
> The result of get_order() is undefined if the size is 0. This may lead to
> invalid shift calculation later caught with UBSAN.
> 
> Replace the zero value with PAGE_SIZE before calling get_order().
> No functional change for valid (non-zero) settings.
> 
> [1]
> UBSAN: shift-out-of-bounds in drivers/scsi/sg.c:1897:13
> shift exponent 64 is too large for 32-bit type 'int'
> CPU: 1 UID: 0 PID: 5832 Comm: syz-executor361 Not tainted 6.14.0-rc2-syzkaller-00185-g128c8f96eb86 #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 12/27/2024
> Call Trace:
>  <TASK>
>  __dump_stack lib/dump_stack.c:94 [inline]
>  dump_stack_lvl+0x16c/0x1f0 lib/dump_stack.c:120
>  ubsan_epilogue lib/ubsan.c:231 [inline]
>  __ubsan_handle_shift_out_of_bounds+0x24f/0x3f0 lib/ubsan.c:468
>  sg_build_indirect.cold+0x1b/0x20 drivers/scsi/sg.c:1897
>  sg_build_reserve+0xc4/0x180 drivers/scsi/sg.c:2007
>  sg_add_sfp drivers/scsi/sg.c:2189 [inline]
>  sg_open+0xc37/0x1910 drivers/scsi/sg.c:348
>  chrdev_open+0x237/0x6a0 fs/char_dev.c:414
>  do_dentry_open+0x735/0x1c40 fs/open.c:956
>  vfs_open+0x82/0x3f0 fs/open.c:1086
>  do_open fs/namei.c:3830 [inline]
>  path_openat+0x1e88/0x2d80 fs/namei.c:3989
>  do_filp_open+0x20c/0x470 fs/namei.c:4016
>  do_sys_openat2+0x17a/0x1e0 fs/open.c:1428
>  do_sys_open fs/open.c:1443 [inline]
>  __do_sys_openat fs/open.c:1459 [inline]
>  __se_sys_openat fs/open.c:1454 [inline]
>  __x64_sys_openat+0x175/0x210 fs/open.c:1454
>  do_syscall_x64 arch/x86/entry/common.c:52 [inline]
>  do_syscall_64+0xcd/0x250 arch/x86/entry/common.c:83
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> 

В рамках взаимодействия с Центром для подготавливаемых патчей следует
вставлять строку

Found by Linux Verification Center ...

> Reported-by: syzbot+270f1c719ee7baab9941 at syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=270f1c719ee7baab9941

Тег Fixes?

> Signed-off-by: Tonofa Boris <b.tonofa at ideco.ru>
> ---
>  drivers/scsi/sg.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/scsi/sg.c b/drivers/scsi/sg.c
> index 1946cc96c172..094dee57da3a 100644
> --- a/drivers/scsi/sg.c
> +++ b/drivers/scsi/sg.c
> @@ -1883,6 +1883,8 @@ sg_build_indirect(Sg_scatter_hold * schp, Sg_fd * sfp, int buff_size)
>  		if (num < PAGE_SIZE) {
>  			scatter_elem_sz = PAGE_SIZE;
>  			scatter_elem_sz_prev = PAGE_SIZE;
> +			if (!num)
> +				num = PAGE_SIZE;
>  		} else
>  			scatter_elem_sz_prev = num;
>  	}
> -- 
> 2.50.0