On Tue, May 07, 2024 at 11:17:57PM +0000, Justin Stitt wrote:
> Running syzkaller with the newly enabled signed integer overflow
> sanitizer produces this report:
>
> [ 195.401651] ------------[ cut here ]------------
> [ 195.404808] UBSAN: signed-integer-overflow in ../fs/open.c:321:15
> [ 195.408739] 9223372036854775807 + 562984447377399 cannot be represented in type 'loff_t' (aka 'long long')
> [ 195.414683] CPU: 1 PID: 703 Comm: syz-executor.0 Not tainted 6.8.0-rc2-00039-g14de58dbe653-dirty #11
> [ 195.420138] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
> [ 195.425804] Call Trace:
> [ 195.427360] <TASK>
> [ 195.428791] dump_stack_lvl+0x93/0xd0
> [ 195.431150] handle_overflow+0x171/0x1b0
> [ 195.433640] vfs_fallocate+0x459/0x4f0
> ...
> [ 195.490053] ------------[ cut here ]------------
> [ 195.493146] UBSAN: signed-integer-overflow in ../fs/open.c:321:61
> [ 195.497030] 9223372036854775807 + 562984447377399 cannot be represented in type 'loff_t' (aka 'long long)
> [ 195.502940] CPU: 1 PID: 703 Comm: syz-executor.0 Not tainted 6.8.0-rc2-00039-g14de58dbe653-dirty #11
> [ 195.508395] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
> [ 195.514075] Call Trace:
> [ 195.515636] <TASK>
> [ 195.517000] dump_stack_lvl+0x93/0xd0
> [ 195.519255] handle_overflow+0x171/0x1b0
> [ 195.521677] vfs_fallocate+0x4cb/0x4f0
> [ 195.524033] __x64_sys_fallocate+0xb2/0xf0
>
> 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 use the check_add_overflow helper to first verify the addition
> stays within the bounds of its type (long long); then we can use that
> sum for the following check.
>
> Link: https://github.com/llvm/llvm-project/pull/82432 [1]
> Closes: https://github.com/KSPP/linux/issues/356
> Cc: linux-hardening@xxxxxxxxxxxxxxx
> Signed-off-by: Justin Stitt <justinstitt@xxxxxxxxxx>
I think this makes the checking more reading too. Thanks
Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
--
Kees Cook
