Currently the code calls mas_start() followed by mas_data_end() if the maple state is MA_START, but mas_start() may return with the maple state node == NULL. This will lead to a null pointer dereference when checking information in the NULL node, which is done in mas_data_end(). Avoid setting the offset if there is no node by waiting until after the maple state is checked for an empty or single entry state. A user could trigger the events to cause a kernel oops by unmapping all vmas to produce an empty maple tree, then mapping a vma that would cause the scenario described above. Reported-by: Marius Fleischer <fleischermarius@xxxxxxxxx> Closes: https://lore.kernel.org/lkml/CAJg=8jyuSxDL6XvqEXY_66M20psRK2J53oBTP+fjV5xpW2-R6w@xxxxxxxxxxxxxx/ Link: https://lore.kernel.org/lkml/CAJg=8jyuSxDL6XvqEXY_66M20psRK2J53oBTP+fjV5xpW2-R6w@xxxxxxxxxxxxxx/ Fixes: 54a611b60590 ("Maple Tree: add new data structure") Tested-by: Marius Fleischer <fleischermarius@xxxxxxxxx> Tested-by: Sidhartha Kumar <sidhartha.kumar@xxxxxxxxxx> Cc: maple-tree@xxxxxxxxxxxxxxxxxxx Cc: linux-mm@xxxxxxxxx Cc: stable@xxxxxxxxxxxxxxx Signed-off-by: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx> --- lib/maple_tree.c | 16 ++++++++-------- 1 file changed, 8 insertions(+), 8 deletions(-) diff --git a/lib/maple_tree.c b/lib/maple_tree.c index 55e1b35bf877..2d7d27e6ae3c 100644 --- a/lib/maple_tree.c +++ b/lib/maple_tree.c @@ -5109,18 +5109,18 @@ int mas_empty_area_rev(struct ma_state *mas, unsigned long min, if (size == 0 || max - min < size - 1) return -EINVAL; - if (mas_is_start(mas)) { + if (mas_is_start(mas)) mas_start(mas); - mas->offset = mas_data_end(mas); - } else if (mas->offset >= 2) { - mas->offset -= 2; - } else if (!mas_rewind_node(mas)) { + else if ((mas->offset < 2) && (!mas_rewind_node(mas))) return -EBUSY; - } - /* Empty set. */ - if (mas_is_none(mas) || mas_is_ptr(mas)) + if (unlikely(mas_is_none(mas) || mas_is_ptr(mas))) return mas_sparse_area(mas, min, max, size, false); + else if (mas->offset >= 2) + mas->offset -= 2; + else + mas->offset = mas_data_end(mas); + /* The start of the window can only be within these values. */ mas->index = min; -- 2.43.0
