param: fix charp parameters set via sysfs
Impact: fix crash on reading from /sys/module/.../ieee80211_default_rc_algo
The module_param type "charp" simply sets a char * pointer in the
module to the parameter in the commandline string: this is why we keep
the (mangled) module command line around. But when set via sysfs (as
about 11 charp parameters can be) this memory is freed on the way
out of the write(). Future reads hit random mem.
So we kstrdup instead: we have to check we're not in early commandline
parsing, and we have to note when we've used it so we can reliably
kfree the parameter when it's next overwritten, and also on module
unload.
(Thanks to Randy Dunlap for CONFIG_SYSFS=n fixes)
Reported-by: Sitsofe Wheeler <sitsofe@yahoo.com>
Diagnosed-by: Frederic Weisbecker <fweisbec@gmail.com>
Tested-by: Frederic Weisbecker <fweisbec@gmail.com>
Tested-by: Christof Schmitt <christof.schmitt@de.ibm.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
diff --git a/kernel/params.c b/kernel/params.c
index a1e3025..de273ec 100644
--- a/kernel/params.c
+++ b/kernel/params.c
@@ -24,6 +24,9 @@
#include <linux/err.h>
#include <linux/slab.h>
+/* We abuse the high bits of "perm" to record whether we kmalloc'ed. */
+#define KPARAM_KMALLOCED 0x80000000
+
#if 0
#define DEBUGP printk
#else
@@ -217,7 +220,19 @@
return -ENOSPC;
}
- *(char **)kp->arg = (char *)val;
+ if (kp->perm & KPARAM_KMALLOCED)
+ kfree(*(char **)kp->arg);
+
+ /* This is a hack. We can't need to strdup in early boot, and we
+ * don't need to; this mangled commandline is preserved. */
+ if (slab_is_available()) {
+ kp->perm |= KPARAM_KMALLOCED;
+ *(char **)kp->arg = kstrdup(val, GFP_KERNEL);
+ if (!kp->arg)
+ return -ENOMEM;
+ } else
+ *(const char **)kp->arg = val;
+
return 0;
}
@@ -571,6 +586,15 @@
}
#endif
+void destroy_params(const struct kernel_param *params, unsigned num)
+{
+ unsigned int i;
+
+ for (i = 0; i < num; i++)
+ if (params[i].perm & KPARAM_KMALLOCED)
+ kfree(*(char **)params[i].arg);
+}
+
static void __init kernel_add_sysfs_param(const char *name,
struct kernel_param *kparam,
unsigned int name_skip)