brcmfmac: Fix out of bounds memory access during fw load

I ended up tracking down some rather nasty issues with f2fs (and other
filesystem modules) constantly crashing on my kernel down to a
combination of out of bounds memory accesses, one of which was coming
from brcmfmac during module load:

[   30.891382] brcmfmac: brcmf_fw_alloc_request: using brcm/brcmfmac4356-sdio for chip BCM4356/2
[   30.894437] ==================================================================
[   30.901581] BUG: KASAN: global-out-of-bounds in brcmf_fw_alloc_request+0x42c/0x480 [brcmfmac]
[   30.909935] Read of size 1 at addr ffff2000024865df by task kworker/6:2/387
[   30.916805]
[   30.918261] CPU: 6 PID: 387 Comm: kworker/6:2 Tainted: G           O      4.20.0-rc3Lyude-Test+ #19
[   30.927251] Hardware name: amlogic khadas-vim2/khadas-vim2, BIOS 2018.07-rc2-armbian 09/11/2018
[   30.935964] Workqueue: events brcmf_driver_register [brcmfmac]
[   30.941641] Call trace:
[   30.944058]  dump_backtrace+0x0/0x3e8
[   30.947676]  show_stack+0x14/0x20
[   30.950968]  dump_stack+0x130/0x1c4
[   30.954406]  print_address_description+0x60/0x25c
[   30.959066]  kasan_report+0x1b4/0x368
[   30.962683]  __asan_report_load1_noabort+0x18/0x20
[   30.967547]  brcmf_fw_alloc_request+0x42c/0x480 [brcmfmac]
[   30.967639]  brcmf_sdio_probe+0x163c/0x2050 [brcmfmac]
[   30.978035]  brcmf_ops_sdio_probe+0x598/0xa08 [brcmfmac]
[   30.983254]  sdio_bus_probe+0x190/0x398
[   30.983270]  really_probe+0x2a0/0xa70
[   30.983296]  driver_probe_device+0x1b4/0x2d8
[   30.994901]  __driver_attach+0x200/0x280
[   30.994914]  bus_for_each_dev+0x10c/0x1a8
[   30.994925]  driver_attach+0x38/0x50
[   30.994935]  bus_add_driver+0x330/0x608
[   30.994953]  driver_register+0x140/0x388
[   31.013965]  sdio_register_driver+0x74/0xa0
[   31.014076]  brcmf_sdio_register+0x14/0x60 [brcmfmac]
[   31.023177]  brcmf_driver_register+0xc/0x18 [brcmfmac]
[   31.023209]  process_one_work+0x654/0x1080
[   31.032266]  worker_thread+0x4f0/0x1308
[   31.032286]  kthread+0x2a8/0x320
[   31.039254]  ret_from_fork+0x10/0x1c
[   31.039269]
[   31.044226] The buggy address belongs to the variable:
[   31.044351]  brcmf_firmware_path+0x11f/0xfffffffffffd3b40 [brcmfmac]
[   31.055601]
[   31.057031] Memory state around the buggy address:
[   31.061800]  ffff200002486480: 04 fa fa fa fa fa fa fa 00 00 00 00 00 00 00 00
[   31.068983]  ffff200002486500: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[   31.068993] >ffff200002486580: 00 00 00 00 00 00 00 00 fa fa fa fa 00 00 00 00
[   31.068999]                                                     ^
[   31.069017]  ffff200002486600: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[   31.096521]  ffff200002486680: 00 00 00 00 00 00 00 00 00 00 00 00 fa fa fa fa
[   31.096528] ==================================================================
[   31.096533] Disabling lock debugging due to kernel taint

It appears that when trying to determine the length of the string in the
alternate firmware path, we make the mistake of not handling the case
where the firmware path is empty correctly. Since strlen(mp_path) can
return 0, we'll end up accessing mp_path[-1] when the firmware_path
isn't provided through the module arguments.

So, fix this by just setting the end char to '\0' by default, and only
changing it if we have a non-zero length. Additionally, use strnlen()
with BRCMF_FW_ALTPATH_LEN instead of strlen() just to be extra safe.

Fixes: 2baa3aaee27f ("brcmfmac: introduce brcmf_fw_alloc_request() function")
Cc: Hante Meuleman <hante.meuleman@broadcom.com>
Cc: Pieter-Paul Giesberts <pieter-paul.giesberts@broadcom.com>
Cc: Franky Lin <franky.lin@broadcom.com>
Cc: Arend van Spriel <arend.vanspriel@broadcom.com>
Cc: Kalle Valo <kvalo@codeaurora.org>
Cc: Arend Van Spriel <arend.vanspriel@broadcom.com>
Cc: Himanshu Jha <himanshujha199640@gmail.com>
Cc: Dan Haab <dhaab@luxul.com>
Cc: Jia-Shyr Chuang <saint.chuang@cypress.com>
Cc: Ian Molton <ian@mnementh.co.uk>
Cc: <stable@vger.kernel.org> # v4.17+
Signed-off-by: Lyude Paul <lyude@redhat.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>

diff --git a/drivers/net/wireless/broadcom/brcm80211/brcmfmac/firmware.c b/drivers/net/wireless/broadcom/brcm80211/brcmfmac/firmware.c
index 72d8c0c3c3a1245cb0eca44ff4464bec508edc4c..dad3c1c7903866cf37574ffb64e43e4a3c0f44cd 100644 (file)
--- a/drivers/net/wireless/broadcom/brcm80211/brcmfmac/firmware.c
+++ b/drivers/net/wireless/broadcom/brcm80211/brcmfmac/firmware.c
@@ -708,8 +708,9 @@ brcmf_fw_alloc_request(u32 chip, u32 chiprev,
        struct brcmf_fw_request *fwreq;
        char chipname[12];
        const char *mp_path;
+       size_t mp_path_len;
        u32 i, j;
-       char end;
+       char end = '\0';
        size_t reqsz;
 
        for (i = 0; i < table_size; i++) {
@@ -734,7 +735,10 @@ brcmf_fw_alloc_request(u32 chip, u32 chiprev,
                   mapping_table[i].fw_base, chipname);
 
        mp_path = brcmf_mp_global.firmware_path;
-       end = mp_path[strlen(mp_path) - 1];
+       mp_path_len = strnlen(mp_path, BRCMF_FW_ALTPATH_LEN);
+       if (mp_path_len)
+               end = mp_path[mp_path_len - 1];
+
        fwreq->n_items = n_fwnames;
 
        for (j = 0; j < n_fwnames; j++) {