linux-kernel - [PATCH v2] regmap: Fix possible double-free in regcache_rbtree

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Date:   Tue, 12 Oct 2021 10:37:35 +0800
From:   Yang Yingliang <yangyingliang@...wei.com>
To:     <linux-kernel@...r.kernel.org>
CC:     <rafael@...nel.org>, <gregkh@...uxfoundation.org>,
        <broonie@...nel.org>
Subject: [PATCH v2] regmap: Fix possible double-free in regcache_rbtree_exit()

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:
 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

To fix this, moving up the assignment of rbnode->block to immediately after
the reallocation has succeeded so that the data structure stays valid even
if the second reallocation fails.

Reported-by: Hulk Robot <hulkci@...wei.com>
Fixes: 3f4ff561bc88b ("regmap: rbtree: Make cache_present bitmap per node")
Signed-off-by: Yang Yingliang <yangyingliang@...wei.com>
---
v2:
  - moving up the assignment of rbnode->block instead of setting
  rbnode->block to NULL.
  - drop some unuseful backtrace in commit message.
---
 drivers/base/regmap/regcache-rbtree.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/drivers/base/regmap/regcache-rbtree.c b/drivers/base/regmap/regcache-rbtree.c
index cfa29dc89bbf..fabf87058d80 100644
--- a/drivers/base/regmap/regcache-rbtree.c
+++ b/drivers/base/regmap/regcache-rbtree.c
@@ -281,14 +281,14 @@ static int regcache_rbtree_insert_to_block(struct regmap *map,
 	if (!blk)
 		return -ENOMEM;
 
+	rbnode->block = blk;
+
 	if (BITS_TO_LONGS(blklen) > BITS_TO_LONGS(rbnode->blklen)) {
 		present = krealloc(rbnode->cache_present,
 				   BITS_TO_LONGS(blklen) * sizeof(*present),
 				   GFP_KERNEL);
-		if (!present) {
-			kfree(blk);
+		if (!present)
 			return -ENOMEM;
-		}
 
 		memset(present + BITS_TO_LONGS(rbnode->blklen), 0,
 		       (BITS_TO_LONGS(blklen) - BITS_TO_LONGS(rbnode->blklen))
@@ -305,7 +305,6 @@ static int regcache_rbtree_insert_to_block(struct regmap *map,
 	}
 
 	/* update the rbnode block, its size and the base register */
-	rbnode->block = blk;
 	rbnode->blklen = blklen;
 	rbnode->base_reg = base_reg;
 	rbnode->cache_present = present;
-- 
2.25.1