[PATCH 3.16 068/134] mwifiex: pcie: fix cmd_buf use-after-free in remove/reset

Ben Hutchings
2017-08-18T13:15:47Z

From: Brian Norris <briannorris@chromium.org>

commit 3c8cb9ad032d737b874e402c59eb51e3c991a144 upstream.

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")
Signed-off-by: Brian Norris <briannorris@chromium.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
[bwh: Backported to 3.16: adjust filename]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
drivers/net/wireless/mwifiex/pcie.c | 7 +++++++
1 file changed, 7 insertions(+)

--- a/drivers/net/wireless/mwifiex/pcie.c
+++ b/drivers/net/wireless/mwifiex/pcie.c
@@ -905,6 +905,7 @@ static int mwifiex_pcie_delete_cmdrsp_bu
if (card && card->cmd_buf) {
mwifiex_unmap_pci_memory(adapter, card->cmd_buf,
PCI_DMA_TODEVICE);
+ dev_kfree_skb_any(card->cmd_buf);
}
return 0;
}
@@ -1446,6 +1447,11 @@ mwifiex_pcie_send_cmd(struct mwifiex_ada
return -1;

card->cmd_buf = skb;
+ /*
+ * Need to keep a reference, since core driver might free up this
+ * buffer before we've unmapped it.
+ */
+ skb_get(skb);

/* To send a command, the driver will:
1. Write the 64bit physical address of the data buffer to
@@ -1542,6 +1548,7 @@ static int mwifiex_pcie_process_cmd_comp
if (card->cmd_buf) {
mwifiex_unmap_pci_memory(adapter, card->cmd_buf,
PCI_DMA_TODEVICE);
+ dev_kfree_skb_any(card->cmd_buf);
card->cmd_buf = NULL;
}