Messages in this thread | | | Subject | debugfs_remove() vs. anything that is dynamic | From | Johannes Berg <> | Date | Fri, 04 Apr 2008 01:56:26 +0200 |
| |
Consider the following trivial module:
--- %< --- #include <linux/module.h> #include <linux/debugfs.h>
static struct dentry *f; static u32 tmp;
int __init mod_enter(void) { f = debugfs_create_u32("tmp-test", 0666, NULL, &tmp);
return 0; }
void __exit mod_leave(void) { debugfs_remove(f); }
module_init(mod_enter); module_exit(mod_leave); MODULE_LICENSE("GPL"); --- >% ---
How do I make that safe?
FWIW, the problem is:
thread 1 thread 2 fd = open("tmp-test")
sleep(30); rmmod test-module
read(fd, buf, 100);
--> accesses now invalid memory because debugfs doesn't actually stop you from accessing "&tmp" after debugfs_remove(). [yes, I actually tested a variation of this where I dynamically allocated the 'tmp' variable, I got the slab poison in my test program]
Personally, I tend to think this makes debugfs rather unusable in modules and with anything that is dynamically allocated [1]. AFAICT sysfs avoids this by having object lifetime imposed by sysfs, but debugfs doesn't work that way.
What am I missing?
johannes
[1] which covers many many current users, it seems at least usbmon, ohci/ehci/uhci-dbg, pktcdvd, fault injection code, blktrace and probably more. [unhandled content-type:application/pgp-signature] | |