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SubjectRe: [PATCH] kobject: Fix slab-out-of-bounds in fill_kobj_path()
On Mon, Dec 19, 2022 at 10:41:03PM +0800, Wang Hai wrote:
> In kobject_get_path(), if kobj->name is changed between calls
> get_kobj_path_length() and fill_kobj_path() and the length becomes
> longer, then fill_kobj_path() will have an out-of-bounds bug.
>
> The actual current problem occurs when the ixgbe probe.
>
> In ixgbe_mii_bus_init(), if the length of netdev->dev.kobj.name
> length becomes longer, out-of-bounds will occur.
>
> cpu0 cpu1
> ixgbe_probe
> register_netdev(netdev)
> netdev_register_kobject
> device_add
> kobject_uevent // Sending ADD events
> systemd-udevd // rename netdev
> dev_change_name
> device_rename
> kobject_rename
> |
> ixgbe_mii_bus_init |
> mdiobus_register |
> __mdiobus_register |
> device_register |
> device_add |
> kobject_uevent |
> kobject_get_path |
> len = get_kobj_path_length // old name |
> path = kzalloc(len, gfp_mask); |
> kobj->name = name;
> /* name length becomes
> * longer
> */
> fill_kobj_path /* kobj path length is
> * longer than path,
> * resulting in out of
> * bounds when filling path
> */
>
> This is the kasan report:
>
> ==================================================================
> BUG: KASAN: slab-out-of-bounds in fill_kobj_path+0x50/0xc0
> Write of size 7 at addr ff1100090573d1fd by task kworker/28:1/673
>
> Workqueue: events work_for_cpu_fn
> Call Trace:
> <TASK>
> dump_stack_lvl+0x34/0x48
> print_address_description.constprop.0+0x86/0x1e7
> print_report+0x36/0x4f
> kasan_report+0xad/0x130
> kasan_check_range+0x35/0x1c0
> memcpy+0x39/0x60
> fill_kobj_path+0x50/0xc0
> kobject_get_path+0x5a/0xc0
> kobject_uevent_env+0x140/0x460
> device_add+0x5c7/0x910
> __mdiobus_register+0x14e/0x490
> ixgbe_probe.cold+0x441/0x574 [ixgbe]
> local_pci_probe+0x78/0xc0
> work_for_cpu_fn+0x26/0x40
> process_one_work+0x3b6/0x6a0
> worker_thread+0x368/0x520
> kthread+0x165/0x1a0
> ret_from_fork+0x1f/0x30
>
> This reproducer triggers that bug:
>
> while:
> do
> rmmod ixgbe
> sleep 0.5
> modprobe ixgbe
> sleep 0.5
>
> When calling fill_kobj_path() to fill path, if the name length of
> kobj becomes longer, return failure and retry.
>
> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> Signed-off-by: Wang Hai <wanghai38@huawei.com>
> ---
> lib/kobject.c | 14 ++++++++++++--
> 1 file changed, 12 insertions(+), 2 deletions(-)

Nice find, and a much better description than was reported here:
https://lore.kernel.org/all/20221216031320.2634-1-alice.chao@mediatek.com/

Alice, does this patch resolve your problem as well?

>
> diff --git a/lib/kobject.c b/lib/kobject.c
> index a0b2dbfcfa23..d129f437b200 100644
> --- a/lib/kobject.c
> +++ b/lib/kobject.c
> @@ -112,7 +112,7 @@ static int get_kobj_path_length(struct kobject *kobj)
> return length;
> }
>
> -static void fill_kobj_path(struct kobject *kobj, char *path, int length)
> +static bool fill_kobj_path(struct kobject *kobj, char *path, int length)

Just return an int and an error value, bool isn't a normal return value,
right?

> {
> struct kobject *parent;
>
> @@ -121,12 +121,16 @@ static void fill_kobj_path(struct kobject *kobj, char *path, int length)
> int cur = strlen(kobject_name(parent));
> /* back up enough to print this name with '/' */
> length -= cur;
> + if (length < 0)
> + return false;

Return -EINVAL or something?

What if length ends up 0 here, is that going to be ok?


> memcpy(path + length, kobject_name(parent), cur);
> *(path + --length) = '/';
> }
>
> pr_debug("kobject: '%s' (%p): %s: path = '%s'\n", kobject_name(kobj),
> kobj, __func__, path);
> +
> + return true;

return 0;

> }
>
> /**
> @@ -140,14 +144,20 @@ char *kobject_get_path(struct kobject *kobj, gfp_t gfp_mask)
> {
> char *path;
> int len;
> + bool ret;

No need for this variable

>
> +retry:
> len = get_kobj_path_length(kobj);
> if (len == 0)
> return NULL;
> path = kzalloc(len, gfp_mask);
> if (!path)
> return NULL;
> - fill_kobj_path(kobj, path, len);
> + ret = fill_kobj_path(kobj, path, len);
> + if (!ret) {

Make this one line:

if (fill_kobj_path(kobj, path, len)) {

But, you now have a loop, what guarantees that you can get out of it?

thanks,

greg k-h

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