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.

Signed-off-by: Lyude Paul lyude@redhat.com

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 --- .../net/wireless/broadcom/brcm80211/brcmfmac/firmware.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/net/wireless/broadcom/brcm80211/brcmfmac/firmware.c b/drivers/net/wireless/broadcom/brcm80211/brcmfmac/firmware.c index 9095b830ae4d..9927079a9ace 100644 --- a/drivers/net/wireless/broadcom/brcm80211/brcmfmac/firmware.c +++ b/drivers/net/wireless/broadcom/brcm80211/brcmfmac/firmware.c @@ -641,8 +641,9 @@ 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++) { @@ -667,7 +668,10 @@ 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++) {