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mm: fix use-after-free in sys_remap_file_pages
commit 4eb919825e6c3c7fb3630d5621f6d11e98a18b3a upstream. remap_file_pages calls mmap_region, which may merge the VMA with other existing VMAs, and free "vma". This can lead to a use-after-free bug. Avoid the bug by remembering vm_flags before calling mmap_region, and not trying to dereference vma later. Signed-off-by: Rik van Riel <riel@redhat.com> Reported-by: Dmitry Vyukov <dvyukov@google.com> Cc: PaX Team <pageexec@freemail.hu> Cc: Kees Cook <keescook@chromium.org> Cc: Michel Lespinasse <walken@google.com> Cc: Cyrill Gorcunov <gorcunov@openvz.org> Cc: Hugh Dickins <hughd@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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@ -203,9 +203,10 @@ get_write_lock:
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if (mapping_cap_account_dirty(mapping)) {
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unsigned long addr;
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struct file *file = get_file(vma->vm_file);
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/* mmap_region may free vma; grab the info now */
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vm_flags = vma->vm_flags;
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addr = mmap_region(file, start, size,
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vma->vm_flags, pgoff);
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addr = mmap_region(file, start, size, vm_flags, pgoff);
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fput(file);
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if (IS_ERR_VALUE(addr)) {
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err = addr;
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@ -213,7 +214,7 @@ get_write_lock:
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BUG_ON(addr != start);
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err = 0;
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}
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goto out;
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goto out_freed;
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}
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mutex_lock(&mapping->i_mmap_mutex);
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flush_dcache_mmap_lock(mapping);
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@ -248,6 +249,7 @@ get_write_lock:
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out:
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if (vma)
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vm_flags = vma->vm_flags;
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out_freed:
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if (likely(!has_write_lock))
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up_read(&mm->mmap_sem);
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else
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