[PATCH V2 1/2] soc: imx8: Fix potential kernel dump in error path

[Anson . Huang]

From: Anson Huang <Anson.Huang@xxxxxxx>

When SoC's revision value is 0, SoC driver will print out
"unknown" in sysfs's revision node, this "unknown" is a
static string which can NOT be freed, this will caused below
kernel dump in later error path which calls kfree:

kernel BUG at mm/slub.c:3942!
Internal error: Oops - BUG: 0 [#1] PREEMPT SMP
Modules linked in:
CPU: 2 PID: 1 Comm: swapper/0 Not tainted 5.2.0-rc4-next-20190611-00023-g705146c-dirty #2197
Hardware name: NXP i.MX8MQ EVK (DT)
pstate: 60000005 (nZCv daif -PAN -UAO)
pc : kfree+0x170/0x1b0
lr : imx8_soc_init+0xc0/0xe4
sp : ffff00001003bd10
x29: ffff00001003bd10 x28: ffff00001121e0a0
x27: ffff000011482000 x26: ffff00001117068c
x25: ffff00001121e100 x24: ffff000011482000
x23: ffff000010fe2b58 x22: ffff0000111b9ab0
x21: ffff8000bd9dfba0 x20: ffff0000111b9b70
x19: ffff7e000043f880 x18: 0000000000001000
x17: ffff000010d05fa0 x16: ffff0000122e0000
x15: 0140000000000000 x14: 0000000030360000
x13: ffff8000b94b5bb0 x12: 0000000000000038
x11: ffffffffffffffff x10: ffffffffffffffff
x9 : 0000000000000003 x8 : ffff8000b9488147
x7 : ffff00001003bc00 x6 : 0000000000000000
x5 : 0000000000000003 x4 : 0000000000000003
x3 : 0000000000000003 x2 : b8793acd604edf00
x1 : ffff7e000043f880 x0 : ffff7e000043f888
Call trace:
 kfree+0x170/0x1b0
 imx8_soc_init+0xc0/0xe4
 do_one_initcall+0x58/0x1b8
 kernel_init_freeable+0x1cc/0x288
 kernel_init+0x10/0x100
 ret_from_fork+0x10/0x18

This patch fixes this potential kernel dump when a chip's
revision is "unknown", it is done by checking whether the
revision space can be freed.

Fixes: a7e26f356ca1 ("soc: imx: Add generic i.MX8 SoC driver")
Signed-off-by: Anson Huang <Anson.Huang@xxxxxxx>
---
Changes since V1:
	- still need the "unknown" info for revision to avoid confusion, so fix this issue
	  by checking whether the revision space can be freed before freeing it.
---
 drivers/soc/imx/soc-imx8.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/soc/imx/soc-imx8.c b/drivers/soc/imx/soc-imx8.c
index 02309a2..5c7f330 100644
--- a/drivers/soc/imx/soc-imx8.c
+++ b/drivers/soc/imx/soc-imx8.c
@@ -155,7 +155,8 @@ static int __init imx8_soc_init(void)
 	return 0;
 
 free_rev:
-	kfree(soc_dev_attr->revision);
+	if (strcmp(soc_dev_attr->revision, "unknown"))
+		kfree(soc_dev_attr->revision);
 free_soc:
 	kfree(soc_dev_attr);
 	of_node_put(root);
-- 
2.7.4