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    Subject[PATCH 1/1] uprobes: mmap_region() corrupts mm->mm_rb if uprobe_mmap() fails

    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 but this is how
    William noticed this bug.

    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

    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.

    And, if nothing else, both mmap_region() and dup_mmap() return
    success if uprobe_mmap() fails. Change them to ignore the error
    code from uprobe_mmap().

    Reported-and-tested-by: William Cohen <>
    Signed-off-by: Oleg Nesterov <>
    Acked-by: Srikar Dronamraju <>
    Cc: <> # v3.5
    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;


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