Re: [PATCH 2/2] uprobes: Use brw_mutex to fix register/unregistervs dup_mmap() race

[Srikar Dronamraju]

> This was always racy, but 268720903f87e0b84b161626c4447b81671b5d18
> "uprobes: Rework register_for_each_vma() to make it O(n)" should be
> blamed anyway, it made everything worse and I didn't notice.
> 
> register/unregister call build_map_info() and then do install/remove
> breakpoint for every mm which mmaps inode/offset. This can obviously
> race with fork()->dup_mmap() in between and we can miss the child.
> 
> uprobe_register() could be easily fixed but unregister is much worse,
> the new mm inherits "int3" from parent and there is no way to detect
> this if uprobe goes away.
> 
> So this patch simply adds brw_start/end_read() around dup_mmap(), and
> brw_start/end_write() into register_for_each_vma().
> 
> This adds 2 new hooks into dup_mmap() but we can kill uprobe_dup_mmap()
> and fold it into uprobe_end_dup_mmap().
> 
> Reported-by: Srikar Dronamraju <srikar@xxxxxxxxxxxxxxxxxx>
> Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>

Acked-by: Srikar Dronamraju <srikar@xxxxxxxxxxxxxxxxxx>

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