[PATCH] regmap: Fix possible double-free in regcache_rbtree_exit()

[Yang Yingliang <yangyingliang@huawei.com>]

In regcache_rbtree_insert_to_block(), when 'present' realloc failed,
the 'blk' which is supposed to assign to 'rbnode->block' will be freed,
so 'rbnode->block' points a freed memory, in the error handling path of
regcache_rbtree_init(), 'rbnode->block' will be freed again in
regcache_rbtree_exit(), KASAN will report double-free as follows:

BUG: KASAN: double-free or invalid-free in kfree+0xce/0x390
Call Trace:
 dump_stack_lvl+0xe2/0x152
 print_address_description.constprop.7+0x21/0x150
 kasan_report_invalid_free+0x6f/0xa0
 __kasan_slab_free+0x125/0x140
 slab_free_freelist_hook+0x10d/0x240
 kfree+0xce/0x390
 regcache_rbtree_exit+0x15d/0x1a0
 regcache_rbtree_init+0x224/0x2c0
 regcache_init+0x88d/0x1310
 __regmap_init+0x3151/0x4a80
 __devm_regmap_init+0x7d/0x100
 madera_spi_probe+0x10f/0x333 [madera_spi]
 spi_probe+0x183/0x210
 really_probe+0x285/0xc30

Set rbnode->block to NULL when the 'present' realloc failed to fix this.

Reported-by: Hulk Robot <hulkci@huawei.com>
Fixes: 3f4ff561bc88b ("regmap: rbtree: Make cache_present bitmap per node")
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
---
 drivers/base/regmap/regcache-rbtree.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/base/regmap/regcache-rbtree.c b/drivers/base/regmap/regcache-rbtree.c
index cfa29dc89bbf..125111688399 100644
--- a/drivers/base/regmap/regcache-rbtree.c
+++ b/drivers/base/regmap/regcache-rbtree.c
@@ -287,6 +287,7 @@ static int regcache_rbtree_insert_to_block(struct regmap *map,
 				   GFP_KERNEL);
 		if (!present) {
 			kfree(blk);
+			rbnode->block = NULL;
 			return -ENOMEM;
 		}
 
-- 
2.25.1