[PATCH] jfs: dtInsertEntry can result in buffer overflow on corrupted jfs filesystems

[Jori Koolstra <jkoolstra@xs4all.nl>]

Below syzbot bug has not been fixed yet. If anyone has time I would
greatly appreciate a review of my patch, so it can be moved along.
It has been sitting for quite a few weeks.

Thanks,
Jori.

> Op 29-10-2025 00:23 CET schreef Jori Koolstra <jkoolstra@xs4all.nl>:
> 
>  
> Syzbot reported a general protection fault in inode_set_ctime_current.
> This resulted from the following circumstances: when creating a new file
> via dtInsert, BT_GETSEARCH may yield a pointer to a dtroot which is
> embedded directly in the jfs_inode_info. When finally dtInsertEntry is
> called, if the freelist field or any next field of a slot of the dtpage
> is corrupted, this may result in memory corruption of the parent
> directory inode.
> 
> In this case the i_sb field was corrupted, which raised the gpf when
> in inode_set_ctime_current i_sb was dereferenced to access s_time_gran.
> 
> I tested the patch using the syzbot reproducer and doing some basic
> filesystem operations on a fresh jfs fs, such as "cp -r /usr/include/
> /mnt/jfs/" and "rm -r /mnt/jfs/include/n*"
> 
> Signed-off-by: Jori Koolstra <jkoolstra@xs4all.nl>
> Reported-by: syzbot+cd7590567cc388f064f3@syzkaller.appspotmail.com
> Closes: https://syzbot.org/bug?extid=cd7590567cc388f064f3