On Tue, May 07, 2024 at 04:54:04AM +0000, Justin Stitt wrote:
> When running syzkaller with the newly reintroduced signed integer wrap
> sanitizer we encounter this splat:
>
> [ 366.015950] UBSAN: signed-integer-overflow in ../drivers/cdrom/cdrom.c:2361:33
> [ 366.021089] -9223372036854775808 - 346321 cannot be represented in type '__s64' (aka 'long long')
> [ 366.025894] program syz-executor.4 is using a deprecated SCSI ioctl, please convert it to SG_IO
> [ 366.027502] CPU: 5 PID: 28472 Comm: syz-executor.7 Not tainted 6.8.0-rc2-00035-gb3ef86b5a957 #1
> [ 366.027512] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
> [ 366.027518] Call Trace:
> [ 366.027523] <TASK>
> [ 366.027533] dump_stack_lvl+0x93/0xd0
> [ 366.027899] handle_overflow+0x171/0x1b0
> [ 366.038787] ata1.00: invalid multi_count 32 ignored
> [ 366.043924] cdrom_ioctl+0x2c3f/0x2d10
> [ 366.063932] ? __pm_runtime_resume+0xe6/0x130
> [ 366.071923] sr_block_ioctl+0x15d/0x1d0
> [ 366.074624] ? __pfx_sr_block_ioctl+0x10/0x10
> [ 366.077642] blkdev_ioctl+0x419/0x500
> [ 366.080231] ? __pfx_blkdev_ioctl+0x10/0x10
> ...
>
> Historically, the signed integer overflow sanitizer did not work in the
> kernel due to its interaction with `-fwrapv` but this has since been
> changed [1] in the newest version of Clang. It was re-enabled in the
> kernel with Commit 557f8c582a9ba8ab ("ubsan: Reintroduce signed overflow
> sanitizer").
>
> Let's rearrange the check to not perform any arithmetic, thus not
> tripping the sanitizer.
>
> Link: https://github.com/llvm/llvm-project/pull/82432 [1]
> Closes: https://github.com/KSPP/linux/issues/354
> Cc: [email protected]
> Signed-off-by: Justin Stitt <[email protected]>
Much more idiomatic. :)
Reviewed-by: Kees Cook <[email protected]>
--
Kees Cook