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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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