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SubjectRe: [PATCH 2/2] configfs: fix kernel infoleak through user-controlled format string
On Tue, Jul 07, 2015 at 10:28:00PM +0800, Nicolas Iooss wrote:
> Some modules call config_item_init_type_name() and
> config_group_init_type_name() with parameter "name" directly controlled
> by userspace. These two functions call config_item_set_name() with this
> name used as a format string, which can be used to leak information such
> as content of the stack to userspace.
>
> For example, make_netconsole_target() in netconsole module calls
> config_item_init_type_name() with the name of a newly-created directory.
> This means that the following commands give some unexpected output, with
> configfs mounted in /sys/kernel/config/ and on a system with a
> configured eth0 ethernet interface:
>
> # modprobe netconsole
> # mkdir /sys/kernel/config/netconsole/target_%lx
> # echo eth0 > /sys/kernel/config/netconsole/target_%lx/dev_name
> # echo 1 > /sys/kernel/config/netconsole/target_%lx/enabled
> # echo eth0 > /sys/kernel/config/netconsole/target_%lx/dev_name
> # dmesg |tail -n1
> [ 142.697668] netconsole: target (target_ffffffffc0ae8080) is
> enabled, disable to update parameters
>
> The directory name is correct but %lx has been interpreted in the
> internal item name, displayed here in the error message used by
> store_dev_name() in drivers/net/netconsole.c.
>
> To fix this, update every caller of config_item_set_name to use "%s"
> when operating on untrusted input.
>
> This issue was found using -Wformat-security gcc flag, once a __printf
> attribute has been added to config_item_set_name().
>
> Signed-off-by: Nicolas Iooss <nicolas.iooss_linux@m4x.org>
> ---
> drivers/usb/gadget/configfs.c | 2 +-
> fs/configfs/item.c | 4 ++--
> 2 files changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/usb/gadget/configfs.c b/drivers/usb/gadget/configfs.c
> index 0495c94a23d7..289e20119fea 100644
> --- a/drivers/usb/gadget/configfs.c
> +++ b/drivers/usb/gadget/configfs.c
> @@ -571,7 +571,7 @@ static struct config_group *function_make(
> if (IS_ERR(fi))
> return ERR_CAST(fi);
>
> - ret = config_item_set_name(&fi->group.cg_item, name);
> + ret = config_item_set_name(&fi->group.cg_item, "%s", name);

No objections from me:

Acked-by: Felipe Balbi <balbi@ti.com>


> if (ret) {
> usb_put_function_instance(fi);
> return ERR_PTR(ret);
> diff --git a/fs/configfs/item.c b/fs/configfs/item.c
> index 4d6a30e76168..b863a09cd2f1 100644
> --- a/fs/configfs/item.c
> +++ b/fs/configfs/item.c
> @@ -115,7 +115,7 @@ void config_item_init_type_name(struct config_item *item,
> const char *name,
> struct config_item_type *type)
> {
> - config_item_set_name(item, name);
> + config_item_set_name(item, "%s", name);
> item->ci_type = type;
> config_item_init(item);
> }
> @@ -124,7 +124,7 @@ EXPORT_SYMBOL(config_item_init_type_name);
> void config_group_init_type_name(struct config_group *group, const char *name,
> struct config_item_type *type)
> {
> - config_item_set_name(&group->cg_item, name);
> + config_item_set_name(&group->cg_item, "%s", name);
> group->cg_item.ci_type = type;
> config_group_init(group);
> }
> --
> 2.4.5
>

--
balbi
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