Messages in this thread Patch in this message | | | From | Mark Rutland <> | Subject | [PATCH] radix-tree: avoid NULL dereference | Date | Fri, 6 Jul 2018 14:41:44 +0100 |
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When idr_alloc() is called for the first time on an IDR (which has no nodes in its radix tree), we end up with calculate_count() calling get_slot_offset() with a NULL node, leading to a NULL pointer dereference caught by UBSAN:
================================================================================ UBSAN: Undefined behaviour in lib/radix-tree.c:123:14 member access within null pointer of type 'const struct radix_tree_node' CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.18.0-rc3+ #14 Hardware name: linux,dummy-virt (DT) Call trace: dump_backtrace+0x0/0x458 show_stack+0x20/0x30 dump_stack+0x18c/0x248 ubsan_epilogue+0x18/0x94 handle_null_ptr_deref+0x1d4/0x228 __ubsan_handle_type_mismatch_v1+0x188/0x1e0 __radix_tree_replace+0x29c/0x2a0 radix_tree_iter_replace+0x58/0x88 idr_alloc_u32+0x240/0x340 idr_alloc+0xe8/0x188 worker_pool_assign_id+0x74/0x128 workqueue_init_early+0x588/0xae4 start_kernel+0x54c/0xb9c ================================================================================
The result of the load is passed into node_tag_get(), which ignores the value when node is NULL. Typically, the compiler inlines both get_slot_offset() and node_tag_get() into calculate_count(), optimizing away the NULL-pointer dereference, and hence this doesn't typically result in a boot failure.
We can't rely on the compiler always doing this, and must avoid dereferencing fields from node when it is potentially NULL.
To do so, this patch folds the generation of offset into tag_get(), such that this only happens when node is not NULL. Callers are updated to pass the relevant slot, rather than the offset derived from it.
Signed-off-by: Mark Rutland <mark.rutland@arm.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Matthew Wilcox <mawilcox@microsoft.com> Cc: valdis.kletnieks@vt.edu --- lib/radix-tree.c | 9 ++++----- 1 file changed, 4 insertions(+), 5 deletions(-)
I beleive this is what Valdis hit [1] back in March. I spotted this while booting an arm64 machine.
Mark.
[1] https://lkml.kernel.org/r/22378.1520883323@turing-police.cc.vt.edu
diff --git a/lib/radix-tree.c b/lib/radix-tree.c index a9e41aed6de4..4c6f409582cb 100644 --- a/lib/radix-tree.c +++ b/lib/radix-tree.c @@ -1137,10 +1137,10 @@ static void replace_slot(void __rcu **slot, void *item, static bool node_tag_get(const struct radix_tree_root *root, const struct radix_tree_node *node, - unsigned int tag, unsigned int offset) + unsigned int tag, void __rcu **slot) { if (node) - return tag_get(node, tag, offset); + return tag_get(node, tag, get_slot_offset(node, slot)); return root_tag_get(root, tag); } @@ -1156,8 +1156,7 @@ static int calculate_count(struct radix_tree_root *root, void *item, void *old) { if (is_idr(root)) { - unsigned offset = get_slot_offset(node, slot); - bool free = node_tag_get(root, node, IDR_FREE, offset); + bool free = node_tag_get(root, node, IDR_FREE, slot); if (!free) return 0; if (!old) @@ -2041,7 +2040,7 @@ void *radix_tree_delete_item(struct radix_tree_root *root, if (!slot) return NULL; if (!entry && (!is_idr(root) || node_tag_get(root, node, IDR_FREE, - get_slot_offset(node, slot)))) + slot))) return NULL; if (item && entry != item) -- 2.11.0
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