Re: [PATCH] proc: nommu: /proc/<pid>/maps: release mmap read lock

[Andrew Morton]

On Thu, 14 Sep 2023 12:30:20 -0400 Ben Wolsieffer <ben.wolsieffer@xxxxxxxxxxx> wrote:

> The no-MMU implementation of /proc/<pid>/map doesn't normally release
> the mmap read lock, because it uses !IS_ERR_OR_NULL(_vml) to determine
> whether to release the lock. Since _vml is NULL when the end of the
> mappings is reached, the lock is not released.
> 
> This code was incorrectly adapted from the MMU implementation, which
> at the time released the lock in m_next() before returning the last entry.
> 
> The MMU implementation has diverged further from the no-MMU version
> since then, so this patch brings their locking and error handling into
> sync, fixing the bug and hopefully avoiding similar issues in the
> future.

Thanks.  Is this bug demonstrable from userspace?  If so, how?