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SubjectRe: Poking ieee80211_default_rc_algo causes kernel lockups
On Mon, Feb 16, 2009 at 08:40:43PM +1030, Rusty Russell wrote:
> On Monday 16 February 2009 06:05:23 Frederic Weisbecker wrote:
> > So the problem seems not related to mac80211 but actually to module parameter management.
> > I'm not sure what is the right fix.
>
> Good spotting. And in fact this bug has been here for quite a while...
>
> The "simple" fix is to kstrdup, but that leaks.
>
> How's this?


Simple solution, and fixes the problem :-)
I've tested the string parameter change and the mac80211 module unloading as well.
No obvious problem.

Tested-by: Frederic Weisbecker <fweisbec@gmail.com>

And also, Reported-by: Sitsofe Wheeler <sitsofe@yahoo.com>

Just one last little thing, it would be good to strip the ending newline
while using echo without -n
ie:

root@nowhere:/sys/module/mac80211/parameters# echo heh_look_at_my_newline > ieee80211_default_rc_algo
root@nowhere:/sys/module/mac80211/parameters# cat ieee80211_default_rc_algo
heh_look_at_my_newline
root@nowhere:/sys/module/mac80211/parameters# echo -n heh_look_at_hum_nothing > ieee80211_default_rc_algo
root@nowhere:/sys/module/mac80211/parameters# cat ieee80211_default_rc_algo
heh_look_at_hum_nothing
root@nowhere:/sys/module/mac80211/parameters#
Because I guess modules don't expect this newline on their strcmp.

Thanks :-)


> param: fix charp parameters set via sysfs (eg. 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().
>
> So we kstrdup instead: this is fine, but it means 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.
>
> Reported-by: Frederic Weisbecker <fweisbec@gmail.com>
> Cc: Frederic Weisbecker <fweisbec@gmail.com>
>
> diff --git a/include/linux/module.h b/include/linux/module.h
> --- a/include/linux/module.h
> +++ b/include/linux/module.h
> @@ -247,6 +247,10 @@ struct module
> const struct kernel_symbol *syms;
> const unsigned long *crcs;
> unsigned int num_syms;
> +
> + /* Kernel parameters. */
> + struct kernel_param *kp;
> + unsigned int num_kp;
>
> /* GPL-only exported symbols. */
> unsigned int num_gpl_syms;
> diff --git a/include/linux/moduleparam.h b/include/linux/moduleparam.h
> --- a/include/linux/moduleparam.h
> +++ b/include/linux/moduleparam.h
> @@ -138,6 +138,9 @@ extern int parse_args(const char *name,
> unsigned num,
> int (*unknown)(char *param, char *val));
>
> +/* Called by module remove. */
> +extern void destroy_params(const struct kernel_param *params, unsigned num);
> +
> /* All the helper functions */
> /* The macros to do compile-time type checking stolen from Jakub
> Jelinek, who IIRC came up with this idea for the 2.4 module init code. */
> diff --git a/kernel/module.c b/kernel/module.c
> --- a/kernel/module.c
> +++ b/kernel/module.c
> @@ -1457,6 +1457,9 @@ static void free_module(struct module *m
> /* Module unload stuff */
> module_unload_free(mod);
>
> + /* Free any allocated parameters. */
> + destroy_params(mod->kp, mod->num_kp);
> +
> /* release any pointers to mcount in this module */
> ftrace_release(mod->module_core, mod->core_size);
>
> @@ -1870,8 +1873,7 @@ static noinline struct module *load_modu
> unsigned int symindex = 0;
> unsigned int strindex = 0;
> unsigned int modindex, versindex, infoindex, pcpuindex;
> - unsigned int num_kp, num_mcount;
> - struct kernel_param *kp;
> + unsigned int num_mcount;
> struct module *mod;
> long err = 0;
> void *percpu = NULL, *ptr = NULL; /* Stops spurious gcc warning */
> @@ -2116,8 +2118,8 @@ static noinline struct module *load_modu
>
> /* Now we've got everything in the final locations, we can
> * find optional sections. */
> - kp = section_objs(hdr, sechdrs, secstrings, "__param", sizeof(*kp),
> - &num_kp);
> + mod->kp = section_objs(hdr, sechdrs, secstrings, "__param",
> + sizeof(*mod->kp), &mod->num_kp);
> mod->syms = section_objs(hdr, sechdrs, secstrings, "__ksymtab",
> sizeof(*mod->syms), &mod->num_syms);
> mod->crcs = section_addr(hdr, sechdrs, secstrings, "__kcrctab");
> @@ -2262,11 +2264,11 @@ static noinline struct module *load_modu
> */
> list_add_rcu(&mod->list, &modules);
>
> - err = parse_args(mod->name, mod->args, kp, num_kp, NULL);
> + err = parse_args(mod->name, mod->args, mod->kp, mod->num_kp, NULL);
> if (err < 0)
> goto unlink;
>
> - err = mod_sysfs_setup(mod, kp, num_kp);
> + err = mod_sysfs_setup(mod, mod->kp, mod->num_kp);
> if (err < 0)
> goto unlink;
> add_sect_attrs(mod, hdr->e_shnum, secstrings, sechdrs);
> diff --git a/kernel/params.c b/kernel/params.c
> --- a/kernel/params.c
> +++ b/kernel/params.c
> @@ -23,6 +23,9 @@
> #include <linux/device.h>
> #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
> @@ -217,7 +220,13 @@ int param_set_charp(const char *val, str
> return -ENOSPC;
> }
>
> - *(char **)kp->arg = (char *)val;
> + if (kp->perm & KPARAM_KMALLOCED)
> + kfree(*(char **)kp->arg);
> +
> + kp->perm |= KPARAM_KMALLOCED;
> + *(char **)kp->arg = kstrdup(val, GFP_KERNEL);
> + if (!kp->arg)
> + return -ENOMEM;
> return 0;
> }
>
> @@ -571,6 +580,15 @@ void module_param_sysfs_remove(struct mo
> }
> #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)



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