Re: [PATCH] uprobes: mmap_region() corrupts mm->mm_rb if uprobe_mmap() fails

[Srikar Dronamraju <srikar@linux.vnet.ibm.com>]

* Oleg Nesterov <oleg@redhat.com> [2012-07-28 18:31:57]:

> https://bugzilla.redhat.com/show_bug.cgi?id=843640
> 
> If mmap_region()->uprobe_mmap() fails, unmap_and_free_vma path
> does unmap_region() but does not remove the soon-to-be-freed vma
> from rb tree (actually there are more problems).
> 
> Perhaps we could do do_munmap() + return in this case, but in fact
> it is simply wrong to abort if uprobe_mmap() fails. Until at least
> we move the !UPROBE_COPY_INSN code from install_breakpoint() to
> uprobe_register().
> 
> For example, uprobe_mmap()->install_breakpoint() can fail if the
> probed insn is not supported (remember, uprobe_register() succeeds
> if nobody mmaps inode/offset), mmap() should not fail in this case.
> 
> dup_mmap()->uprobe_mmap() is wrong too by the same reason, fork()
> can race with uprobe_register() and fail for no reason if it wins
> the race and does install_breakpoint() first.
> 
> Change mmap_region() and dup_mmap() to ignore the error code from
> uprobe_mmap().
> 
> Reported-by: William Cohen <wcohen@redhat.com>
> Signed-off-by: Oleg Nesterov <oleg@redhat.com>
> Cc: <stable@vger.kernel.org> # v3.5

After discussions with Oleg, its very clear that this apt fix for now.

Acked-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>

> ---
>  kernel/fork.c |    4 ++--
>  mm/mmap.c     |    5 ++---
>  2 files changed, 4 insertions(+), 5 deletions(-)
> 
> diff --git a/kernel/fork.c b/kernel/fork.c
> index ab5211b..54bb88a 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -454,8 +454,8 @@ static int dup_mmap(struct mm_struct *mm, struct mm_struct *oldmm)
>  		if (retval)
>  			goto out;
> 
> -		if (file && uprobe_mmap(tmp))
> -			goto out;
> +		if (file)
> +			uprobe_mmap(tmp);
>  	}
>  	/* a new mm has just been created */
>  	arch_dup_mmap(oldmm, mm);
> diff --git a/mm/mmap.c b/mm/mmap.c
> index 4fe2697..f25fd3f 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -1355,9 +1355,8 @@ out:
>  	} else if ((flags & MAP_POPULATE) && !(flags & MAP_NONBLOCK))
>  		make_pages_present(addr, addr + len);
> 
> -	if (file && uprobe_mmap(vma))
> -		/* matching probes but cannot insert */
> -		goto unmap_and_free_vma;
> +	if (file)
> +		uprobe_mmap(vma);
> 
>  	return addr;
> 
> -- 
> 1.5.5.1
> 
>