Re: [PATCH v3] proc: fix missing pde_set_flags() for net proc files

[Stefano Brivio <sbrivio@redhat.com>]

On Thu, 21 Aug 2025 18:58:06 +0800
wangzijie <wangzijie1@honor.com> wrote:

> To avoid potential UAF issues during module removal races, we use pde_set_flags()
> to save proc_ops flags in PDE itself before proc_register(), and then use
> pde_has_proc_*() helpers instead of directly dereferencing pde->proc_ops->*.
> 
> However, the pde_set_flags() call was missing when creating net related proc files.
> This omission caused incorrect behavior which FMODE_LSEEK was being cleared
> inappropriately in proc_reg_open() for net proc files. Lars reported it in this link[1].
> 
> Fix this by ensuring pde_set_flags() is called when register proc entry, and add
> NULL check for proc_ops in pde_set_flags().
> 
> [1]: https://lore.kernel.org/all/20250815195616.64497967@chagall.paradoxon.rec/
> 
> Fixes: ff7ec8dc1b64 ("proc: use the same treatment to check proc_lseek as ones for proc_read_iter et.al")
> Cc: stable@vger.kernel.org
> Reported-by: Lars Wendler <polynomial-c@gmx.de>
> Signed-off-by: wangzijie <wangzijie1@honor.com>

Tested-by: Stefano Brivio <sbrivio@redhat.com>

For the records, see also my report and obsolete patch at:

  https://lore.kernel.org/linux-fsdevel/20250822172335.3187858-1-sbrivio@redhat.com/

-- 
Stefano