[PATCH 6.0 0372/1073] mtd: core: Fix refcount error in del_mtd_device()

Greg Kroah-Hartman
2022-12-28T15:42:20Z

From: Shang XiaoJing <shangxiaojing@huawei.com>

[ Upstream commit 56570bdad5e31c5c538cd6efff5c4510256e1bb4 ]

del_mtd_device() will call of_node_put() to mtd_get_of_node(mtd), which
is mtd->dev.of_node. However, memset(&mtd->dev, 0) is called before
of_node_put(). As the result, of_node_put() won't do anything in
del_mtd_device(), and causes the refcount leak.

del_mtd_device()
memset(&mtd->dev, 0, sizeof(mtd->dev) # clear mtd->dev
of_node_put()
mtd_get_of_node(mtd) # mtd->dev is cleared, can't locate of_node
# of_node_put(NULL) won't do anything

Fix the error by caching the pointer of the device_node.

OF: ERROR: memory leak, expected refcount 1 instead of 2,
of_node_get()/of_node_put() unbalanced - destroy cset entry: attach
overlay node /spi/spi-sram@0
CPU: 3 PID: 275 Comm: python3 Tainted: G N 6.1.0-rc3+ #54
0d8a1edddf51f172ff5226989a7565c6313b08e2
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
rel-1.15.0-0-g2dd4b9b3f840-prebuilt.qemu.org 04/01/2014
Call Trace:
<TASK>
dump_stack_lvl+0x67/0x83
kobject_get+0x155/0x160
of_node_get+0x1f/0x30
of_fwnode_get+0x43/0x70
fwnode_handle_get+0x54/0x80
fwnode_get_nth_parent+0xc9/0xe0
fwnode_full_name_string+0x3f/0xa0
device_node_string+0x30f/0x750
pointer+0x598/0x7a0
vsnprintf+0x62d/0x9b0
...
cfs_overlay_release+0x30/0x90
config_item_release+0xbe/0x1a0
config_item_put+0x5e/0x80
configfs_rmdir+0x3bd/0x540
vfs_rmdir+0x18c/0x320
do_rmdir+0x198/0x330
__x64_sys_rmdir+0x2c/0x40
do_syscall_64+0x37/0x90
entry_SYSCALL_64_after_hwframe+0x63/0xcd

Fixes: 00596576a051 ("mtd: core: clear out unregistered devices a bit more")
Signed-off-by: Shang XiaoJing <shangxiaojing@huawei.com>
[<miquel.raynal@bootlin.com>: Light reword of the commit log]
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20221119063915.11108-1-shangxiaojing@huawei.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/mtd/mtdcore.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/mtd/mtdcore.c b/drivers/mtd/mtdcore.c
index 37050c551880..c14196bbf008 100644
--- a/drivers/mtd/mtdcore.c
+++ b/drivers/mtd/mtdcore.c
@@ -776,6 +776,7 @@ int del_mtd_device(struct mtd_info *mtd)
{
int ret;
struct mtd_notifier *not;
+ struct device_node *mtd_of_node;

mutex_lock(&mtd_table_mutex);

@@ -794,6 +795,7 @@ int del_mtd_device(struct mtd_info *mtd)
mtd->index, mtd->name, mtd->usecount);
ret = -EBUSY;
} else {
+ mtd_of_node = mtd_get_of_node(mtd);
debugfs_remove_recursive(mtd->dbg.dfs_dir);

/* Try to remove the NVMEM provider */
@@ -805,7 +807,7 @@ int del_mtd_device(struct mtd_info *mtd)
memset(&mtd->dev, 0, sizeof(mtd->dev));

idr_remove(&mtd_idr, mtd->index);
- of_node_put(mtd_get_of_node(mtd));
+ of_node_put(mtd_of_node);

module_put(THIS_MODULE);
ret = 0;
--
2.35.1