Re: [PATCH] comedi: Fix potential memory leak in comedi_init()
From: Ian Abbott
Date: Tue Nov 01 2022 - 11:59:59 EST
On 01/11/2022 11:57, shangxiaojing wrote:
On 2022/11/1 19:40, Ian Abbott wrote:
On 01/11/2022 06:16, shangxiaojing wrote:
On 2022/11/1 12:45, Greg KH wrote:
On Tue, Nov 01, 2022 at 11:21:25AM +0800, Shang XiaoJing wrote:
comedi_init() will goto out_unregister_chrdev_region if cdev_add()
failed, which won't free the resource alloced in kobject_set_name().
Call kfree_const() to free the leaked name before goto
out_unregister_chrdev_region.
unreferenced object 0xffff8881000fa8c0 (size 8):
comm "modprobe", pid 239, jiffies 4294905173 (age 51.308s)
hex dump (first 8 bytes):
63 6f 6d 65 64 69 00 ff comedi..
backtrace:
[<000000005f9878f7>] __kmalloc_node_track_caller+0x4c/0x1c0
[<000000000fd70302>] kstrdup+0x3f/0x70
[<000000009428bc33>] kstrdup_const+0x46/0x60
[<00000000ed50d9de>] kvasprintf_const+0xdb/0xf0
[<00000000b2766964>] kobject_set_name_vargs+0x3c/0xe0
[<00000000f2424ef7>] kobject_set_name+0x62/0x90
[<000000005d5a125b>] 0xffffffffa0013098
[<00000000f331e663>] do_one_initcall+0x7a/0x380
[<00000000aa7bac96>] do_init_module+0x5c/0x230
[<000000005fd72335>] load_module+0x227d/0x2420
[<00000000ad550cf1>] __do_sys_finit_module+0xd5/0x140
[<00000000069a60c5>] do_syscall_64+0x3f/0x90
[<00000000c5e0d521>] entry_SYSCALL_64_after_hwframe+0x63/0xcd
Fixes: ed9eccbe8970 ("Staging: add comedi core")
Signed-off-by: Shang XiaoJing <shangxiaojing@xxxxxxxxxx>
---
drivers/comedi/comedi_fops.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)
diff --git a/drivers/comedi/comedi_fops.c
b/drivers/comedi/comedi_fops.c
index e2114bcf815a..2c508c2cf6f6 100644
--- a/drivers/comedi/comedi_fops.c
+++ b/drivers/comedi/comedi_fops.c
@@ -3379,8 +3379,11 @@ static int __init comedi_init(void)
retval = cdev_add(&comedi_cdev, MKDEV(COMEDI_MAJOR, 0),
COMEDI_NUM_MINORS);
- if (retval)
+ if (retval) {
+ kfree_const(comedi_cdev.kobj.name);
+ comedi_cdev.kobj.name = NULL;
goto out_unregister_chrdev_region;
+ }
A driver should never have to poke around in the internals of a cdev
object like this. Please fix the cdev core to not need this if
cdev_add() fails.
Or at least there should be a function that can be called to undo the
allocations of kobject_set_name().
It's ok to add a pair function, but maybe only one place where used
cdev_add() need free name. Your mean all "kfree_const(name);" should be
replaced to the new function?
Hi,
I had checked all 67 places that used cdev_add(), and only the
following 5 functions set the name before the cdev_add():
1. comedi_init(), will memleak and will be fixed by this patch.
2. hfi1_cdev_init(), won't memleak.
3. qib_cdev_init(), won't memleak.
4. uio_major_init(), won't memleak.
5. __register_chrdev(), won't memleak.
As the result, I just fix the code in comedi_init(). Should I still
fix the cdev core code, which is free the name in cdev_add() fail path?
I'm stuck trying to work out why hfi1_cdev_init() doesn't have the
same problem when cdev_add() returns an error.
Only user_add() calls the hfi1_cdev_init(), and will call user_remove()
if hfi1_cdev_init() failed. In user_remove(), hfi1_cdev_cleanup() will
call cdev_del().
No it won't. hfi1_cdev_cleanup() only calls cdev_del() if device is
non-null, but device will be null if the call to cdev_add() failed in
hfi1_cdev_init().
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