linux-kernel - Re: [Bug] UBSAN: shift-out-of-bounds in sg_build

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Date: Fri, 12 Apr 2024 15:49:24 -0700
From: Bart Van Assche <bvanassche@....org>
To: Sam Sun <samsun1006219@...il.com>
Cc: linux-kernel@...r.kernel.org, linux-scsi@...r.kernel.org,
 martin.petersen@...cle.com, jejb@...ux.ibm.com, dgilbert@...erlog.com,
 syzkaller@...glegroups.com, xrivendell7@...il.com
Subject: Re: [Bug] UBSAN: shift-out-of-bounds in sg_build_indirect

On 4/10/24 6:17 PM, Sam Sun wrote:
> On Wed, Apr 10, 2024 at 12:59 AM Bart Van Assche <bvanassche@....org> wrote:
>>
>> On 4/9/24 05:51, Sam Sun wrote:
>>> We further analyzed the root cause of this bug. In function
>>> sg_build_indirect of drivers/scsi/sg.c, variable order of line 1900 is
>>> calculated out using get_order(num), and num comes from
>>> scatter_elem_sz. If scatter_elem_sz is equal or below zero, the order
>>> returned will be 52, so that PAGE_SHIFT + order is 64, which is larger
>>> than 32 bits int range, causing shift-out-of bound. This bug is tested
>>> and still remains in the latest upstream linux (6.9-rc3).
>>> If you have any questions, please contact us.
>>
>> Thank you for having root-caused this issue and also for having shared
>> your root-cause analysis. Do you perhaps plan to post a patch that fixes
>> this issue?
> 
> Sure, I am glad to help! But it is my first time submitting a patch, I
> need to find some instructions. I would appreciate if you could help
> me out. Also, I need to double check the patch to avoid introducing a
> new one. It might take some time.

The process for contributing a patch is as follows:
1. Clone the Linux kernel tree for the subsystem you want to contribute
    to. For SCSI, this is the for-next branch in
    git://git.kernel.org/pub/scm/linux/kernel/git/mkp/scsi.git
2. Make your changes to the code.
3. Commit your changes (git commit -as), chose a patch title and explain
    what has been changed and also why.
4. Convert your changes into a patch, e.g. by running this command:
      git format-patch -1
5. Check the patch with scripts/checkpatch.pl.
6. Send your patch with git send-email to Martin Petersen and Cc the
    linux-scsi mailing list.

More information is available here:
https://docs.kernel.org/process/submitting-patches.html

Best regards,

Bart.