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    Subject[PATCH 5.7 013/124] uprobes: __replace_page() avoid BUG in munlock_vma_page()
    Date
    From: Hugh Dickins <hughd@google.com>

    commit c17c3dc9d08b9aad9a55a1e53f205187972f448e upstream.

    syzbot crashed on the VM_BUG_ON_PAGE(PageTail) in munlock_vma_page(), when
    called from uprobes __replace_page(). Which of many ways to fix it?
    Settled on not calling when PageCompound (since Head and Tail are equals
    in this context, PageCompound the usual check in uprobes.c, and the prior
    use of FOLL_SPLIT_PMD will have cleared PageMlocked already).

    Fixes: 5a52c9df62b4 ("uprobe: use FOLL_SPLIT_PMD instead of FOLL_SPLIT")
    Reported-by: syzbot <syzkaller@googlegroups.com>
    Signed-off-by: Hugh Dickins <hughd@google.com>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    Reviewed-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
    Acked-by: Song Liu <songliubraving@fb.com>
    Acked-by: Oleg Nesterov <oleg@redhat.com>
    Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
    Cc: <stable@vger.kernel.org> [5.4+]
    Link: http://lkml.kernel.org/r/alpine.LSU.2.11.2008161338360.20413@eggly.anvils
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    kernel/events/uprobes.c | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    --- a/kernel/events/uprobes.c
    +++ b/kernel/events/uprobes.c
    @@ -211,7 +211,7 @@ static int __replace_page(struct vm_area
    try_to_free_swap(old_page);
    page_vma_mapped_walk_done(&pvmw);

    - if (vma->vm_flags & VM_LOCKED)
    + if ((vma->vm_flags & VM_LOCKED) && !PageCompound(old_page))
    munlock_vma_page(old_page);
    put_page(old_page);


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