CVE-2024-26895

In the Linux kernel, the following vulnerability has been resolved:

wifi: wilc1000: prevent use-after-free on vif when cleaning up all interfaces

wilc_netdev_cleanup currently triggers a KASAN warning, which can be

observed on interface registration error path, or simply by

removing the module/unbinding device from driver:

echo spi0.1 > /sys/bus/spi/drivers/wilc1000_spi/unbind

==================================================================

BUG: KASAN: slab-use-after-free in wilc_netdev_cleanup+0x508/0x5cc

Read of size 4 at addr c54d1ce8 by task sh/86

CPU: 0 PID: 86 Comm: sh Not tainted 6.8.0-rc1+ #117

Hardware name: Atmel SAMA5

unwind_backtrace from show_stack+0x18/0x1c

show_stack from dump_stack_lvl+0x34/0x58

dump_stack_lvl from print_report+0x154/0x500

print_report from kasan_report+0xac/0xd8

kasan_report from wilc_netdev_cleanup+0x508/0x5cc

wilc_netdev_cleanup from wilc_bus_remove+0xc8/0xec

wilc_bus_remove from spi_remove+0x8c/0xac

spi_remove from device_release_driver_internal+0x434/0x5f8

device_release_driver_internal from unbind_store+0xbc/0x108

unbind_store from kernfs_fop_write_iter+0x398/0x584

kernfs_fop_write_iter from vfs_write+0x728/0xf88

vfs_write from ksys_write+0x110/0x1e4

ksys_write from ret_fast_syscall+0x0/0x1c

[...]

Allocated by task 1:

kasan_save_track+0x30/0x5c

__kasan_kmalloc+0x8c/0x94

__kmalloc_node+0x1cc/0x3e4

kvmalloc_node+0x48/0x180

alloc_netdev_mqs+0x68/0x11dc

alloc_etherdev_mqs+0x28/0x34

wilc_netdev_ifc_init+0x34/0x8ec

wilc_cfg80211_init+0x690/0x910

wilc_bus_probe+0xe0/0x4a0

spi_probe+0x158/0x1b0

really_probe+0x270/0xdf4

__driver_probe_device+0x1dc/0x580

driver_probe_device+0x60/0x140

__driver_attach+0x228/0x5d4

bus_for_each_dev+0x13c/0x1a8

bus_add_driver+0x2a0/0x608

driver_register+0x24c/0x578

do_one_initcall+0x180/0x310

kernel_init_freeable+0x424/0x484

kernel_init+0x20/0x148

ret_from_fork+0x14/0x28

Freed by task 86:

kasan_save_track+0x30/0x5c

kasan_save_free_info+0x38/0x58

__kasan_slab_free+0xe4/0x140

kfree+0xb0/0x238

device_release+0xc0/0x2a8

kobject_put+0x1d4/0x46c

netdev_run_todo+0x8fc/0x11d0

wilc_netdev_cleanup+0x1e4/0x5cc

wilc_bus_remove+0xc8/0xec

spi_remove+0x8c/0xac

device_release_driver_internal+0x434/0x5f8

unbind_store+0xbc/0x108

kernfs_fop_write_iter+0x398/0x584

vfs_write+0x728/0xf88

ksys_write+0x110/0x1e4

ret_fast_syscall+0x0/0x1c

[...]

David Mosberger-Tan initial investigation [1] showed that this

use-after-free is due to netdevice unregistration during vif list

traversal. When unregistering a net device, since the needs_free_netdev has

been set to true during registration, the netdevice object is also freed,

and as a consequence, the corresponding vif object too, since it is

attached to it as private netdevice data. The next occurrence of the loop

then tries to access freed vif pointer to the list to move forward in the

list.

Fix this use-after-free thanks to two mechanisms:

- navigate in the list with list_for_each_entry_safe, which allows to

safely modify the list as we go through each element. For each element,

remove it from the list with list_del_rcu

- make sure to wait for RCU grace period end after each vif removal to make

sure it is safe to free the corresponding vif too (through

unregister_netdev)

Since we are in a RCU "modifier" path (not a "reader" path), and because

such path is expected not to be concurrent to any other modifier (we are

using the vif_mutex lock), we do not need to use RCU list API, that's why

we can benefit from list_for_each_entry_safe.

[1] https://lore.kernel.org/linux-wireless/[email protected]/