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



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