mwifiex: pcie: fix cmd_buf use-after-free in remove/reset

mwifiex: pcie: fix cmd_buf use-after-free in remove/reset

Command buffers (skb's) are allocated by the main driver, and freed upon
the last use. That last use is often in mwifiex_free_cmd_buffer(). In
the meantime, if the command buffer gets used by the PCI driver, we map
it as DMA-able, and store the mapping information in the 'cb' memory.

However, if a command was in-flight when resetting the device (and
therefore was still mapped), we don't get a chance to unmap this memory
until after the core has cleaned up its command handling.

Let's keep a refcount within the PCI driver, so we ensure the memory
only gets freed after we've finished unmapping it.

Noticed by KASAN when forcing a reset via:

  echo 1 > /sys/bus/pci/.../reset

The same code path can presumably be exercised in remove() and
shutdown().

[  205.390377] mwifiex_pcie 0000:01:00.0: info: shutdown mwifiex...
[  205.400393] ==================================================================
[  205.407719] BUG: KASAN: use-after-free in mwifiex_unmap_pci_memory.isra.14+0x4c/0x100 [mwifiex_pcie] at addr ffffffc0ad471b28
[  205.419040] Read of size 16 by task bash/1913
[  205.423421] =============================================================================
[  205.431625] BUG skbuff_head_cache (Tainted: G    B          ): kasan: bad access detected
[  205.439815] -----------------------------------------------------------------------------
[  205.439815]
[  205.449534] INFO: Allocated in __build_skb+0x48/0x114 age=1311 cpu=4 pid=1913
[  205.456709] 	alloc_debug_processing+0x124/0x178
[  205.461282] 	___slab_alloc.constprop.58+0x528/0x608
[  205.466196] 	__slab_alloc.isra.54.constprop.57+0x44/0x54
[  205.471542] 	kmem_cache_alloc+0xcc/0x278
[  205.475497] 	__build_skb+0x48/0x114
[  205.479019] 	__netdev_alloc_skb+0xe0/0x170
[  205.483244] 	mwifiex_alloc_cmd_buffer+0x68/0xdc [mwifiex]
[  205.488759] 	mwifiex_init_fw+0x40/0x6cc [mwifiex]
[  205.493584] 	_mwifiex_fw_dpc+0x158/0x520 [mwifiex]
[  205.498491] 	mwifiex_reinit_sw+0x2c4/0x398 [mwifiex]
[  205.503510] 	mwifiex_pcie_reset_notify+0x114/0x15c [mwifiex_pcie]
[  205.509643] 	pci_reset_notify+0x5c/0x6c
[  205.513519] 	pci_reset_function+0x6c/0x7c
[  205.517567] 	reset_store+0x68/0x98
[  205.521003] 	dev_attr_store+0x54/0x60
[  205.524705] 	sysfs_kf_write+0x9c/0xb0
[  205.528413] INFO: Freed in __kfree_skb+0xb0/0xbc age=131 cpu=4 pid=1913
[  205.535064] 	free_debug_processing+0x264/0x370
[  205.539550] 	__slab_free+0x84/0x40c
[  205.543075] 	kmem_cache_free+0x1c8/0x2a0
[  205.547030] 	__kfree_skb+0xb0/0xbc
[  205.550465] 	consume_skb+0x164/0x178
[  205.554079] 	__dev_kfree_skb_any+0x58/0x64
[  205.558304] 	mwifiex_free_cmd_buffer+0xa0/0x158 [mwifiex]
[  205.563817] 	mwifiex_shutdown_drv+0x578/0x5c4 [mwifiex]
[  205.569164] 	mwifiex_shutdown_sw+0x178/0x310 [mwifiex]
[  205.574353] 	mwifiex_pcie_reset_notify+0xd4/0x15c [mwifiex_pcie]
[  205.580398] 	pci_reset_notify+0x5c/0x6c
[  205.584274] 	pci_dev_save_and_disable+0x24/0x6c
[  205.588837] 	pci_reset_function+0x30/0x7c
[  205.592885] 	reset_store+0x68/0x98
[  205.596324] 	dev_attr_store+0x54/0x60
[  205.600017] 	sysfs_kf_write+0x9c/0xb0
...
[  205.800488] Call trace:
[  205.802980] [<ffffffc00020a69c>] dump_backtrace+0x0/0x190
[  205.808415] [<ffffffc00020a96c>] show_stack+0x20/0x28
[  205.813506] [<ffffffc0005d020c>] dump_stack+0xa4/0xcc
[  205.818598] [<ffffffc0003be44c>] print_trailer+0x158/0x168
[  205.824120] [<ffffffc0003be5f0>] object_err+0x4c/0x5c
[  205.829210] [<ffffffc0003c45bc>] kasan_report+0x334/0x500
[  205.834641] [<ffffffc0003c3994>] check_memory_region+0x20/0x14c
[  205.840593] [<ffffffc0003c3b14>] __asan_loadN+0x14/0x1c
[  205.845879] [<ffffffbffc46171c>] mwifiex_unmap_pci_memory.isra.14+0x4c/0x100 [mwifiex_pcie]
[  205.854282] [<ffffffbffc461864>] mwifiex_pcie_delete_cmdrsp_buf+0x94/0xa8 [mwifiex_pcie]
[  205.862421] [<ffffffbffc462028>] mwifiex_pcie_free_buffers+0x11c/0x158 [mwifiex_pcie]
[  205.870302] [<ffffffbffc4620d4>] mwifiex_pcie_down_dev+0x70/0x80 [mwifiex_pcie]
[  205.877736] [<ffffffbffc1397a8>] mwifiex_shutdown_sw+0x190/0x310 [mwifiex]
[  205.884658] [<ffffffbffc4606b4>] mwifiex_pcie_reset_notify+0xd4/0x15c [mwifiex_pcie]
[  205.892446] [<ffffffc000635f54>] pci_reset_notify+0x5c/0x6c
[  205.898048] [<ffffffc00063a044>] pci_dev_save_and_disable+0x24/0x6c
[  205.904350] [<ffffffc00063cf0c>] pci_reset_function+0x30/0x7c
[  205.910134] [<ffffffc000641118>] reset_store+0x68/0x98
[  205.915312] [<ffffffc000771588>] dev_attr_store+0x54/0x60
[  205.920750] [<ffffffc00046f53c>] sysfs_kf_write+0x9c/0xb0
[  205.926182] [<ffffffc00046dfb0>] kernfs_fop_write+0x184/0x1f8
[  205.931963] [<ffffffc0003d64f4>] __vfs_write+0x6c/0x17c
[  205.937221] [<ffffffc0003d7164>] vfs_write+0xf0/0x1c4
[  205.942310] [<ffffffc0003d7da0>] SyS_write+0x78/0xd8
[  205.947312] [<ffffffc000204634>] el0_svc_naked+0x24/0x28
...
[  205.998268] ==================================================================

This bug has been around in different forms for a while. It was sort of
noticed in commit 955ab095c51a ("mwifiex: Do not kfree cmd buf while
unregistering PCIe"), but it just fixed the double-free, without
acknowledging the potential for use-after-free.

Fixes: fc3314609047 ("mwifiex: use pci_alloc/free_consistent APIs for PCIe")
Cc: <stable@vger.kernel.org>
Signed-off-by: Brian Norris <briannorris@chromium.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>