[PATCH] regmap: debugfs: check count when read regmap file

[peng . fan]

From: Peng Fan <peng.fan@xxxxxxx>

When executing the following command, we met kernel dump.
dmesg -c > /dev/null; cd /sys;
for i in `ls /sys/kernel/debug/regmap/* -d`; do
	echo "Checking regmap in $i";
	cat $i/registers;
done && grep -ri "0x02d0" *;

------------[ cut here ]------------
WARNING: CPU: 0 PID: 6406 at mm/page_alloc.c:4738 __alloc_pages_nodemask+0x2c8/0xda4
Modules linked in: mx6s_capture ov5640_camera_v2 galcore(O) [last unloaded: snvs_ui]
CPU: 0 PID: 6406 Comm: grep Tainted: G           O      5.4.3-lts-lf-5.4.y+g54cbaf43e23e #1
Hardware name: Freescale i.MX6 SoloX (Device Tree)
[<80110770>] (unwind_backtrace) from [<8010b650>] (show_stack+0x10/0x14)
[<8010b650>] (show_stack) from [<80b3770c>] (dump_stack+0x90/0xa4)
[<80b3770c>] (dump_stack) from [<80130310>] (__warn+0xbc/0xd8)
[<80130310>] (__warn) from [<80130390>] (warn_slowpath_fmt+0x64/0xc4)
[<80130390>] (warn_slowpath_fmt) from [<80214328>] (__alloc_pages_nodemask+0x2c8/0xda4)
[<80214328>] (__alloc_pages_nodemask) from [<801f4ba8>] (kmalloc_order+0x1c/0x4c)
[<801f4ba8>] (kmalloc_order) from [<8061e360>] (regmap_read_debugfs+0x64/0x39c)
[<8061e360>] (regmap_read_debugfs) from [<8061e6f0>] (regmap_map_read_file+0x28/0x30)
[<8061e6f0>] (regmap_map_read_file) from [<803c0614>] (full_proxy_read+0x54/0x70)
[<803c0614>] (full_proxy_read) from [<8022c68c>] (__vfs_read+0x30/0x1c4)
[<8022c68c>] (__vfs_read) from [<8022c8b4>] (vfs_read+0x94/0x110)
[<8022c8b4>] (vfs_read) from [<8022cb98>] (ksys_read+0x64/0xec)
[<8022cb98>] (ksys_read) from [<80101000>] (ret_fast_syscall+0x0/0x54)
Exception stack(0xa868bfa8 to 0xa868bff0)
bfa0:                   03001000 03000000 00000006 70e0e000 03000000 00000000
bfc0: 03001000 03000000 76fa53d0 00000003 00000006 70e0d008 00040298 70e0e000
bfe0: 00000003 7ead45a0 76ea2cd7 76e2ed16
---[ end trace f0a1fccbc20d20ff ]---

It is because the count value is too big, and kmalloc fails.
So add a check to allow only max->max_register as max count.

Signed-off-by: Peng Fan <peng.fan@xxxxxxx>
---
 drivers/base/regmap/regmap-debugfs.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/base/regmap/regmap-debugfs.c b/drivers/base/regmap/regmap-debugfs.c
index e72843fe41df..a375cb2ebac9 100644
--- a/drivers/base/regmap/regmap-debugfs.c
+++ b/drivers/base/regmap/regmap-debugfs.c
@@ -283,9 +283,10 @@ static ssize_t regmap_map_read_file(struct file *file, char __user *user_buf,
 				    size_t count, loff_t *ppos)
 {
 	struct regmap *map = file->private_data;
+	size_t num = count > map->max_register ? map->max_register : count;
 
 	return regmap_read_debugfs(map, 0, map->max_register, user_buf,
-				   count, ppos);
+				   num, ppos);
 }
 
 #undef REGMAP_ALLOW_WRITE_DEBUGFS
@@ -371,6 +372,8 @@ static ssize_t regmap_reg_ranges_read_file(struct file *file,
 	if (*ppos < 0 || !count)
 		return -EINVAL;
 
+	count = (count + *ppos) > map->max_register ? map->max_register : count;
+
 	buf = kmalloc(count, GFP_KERNEL);
 	if (!buf)
 		return -ENOMEM;
-- 
2.16.4