Re: [PATCH] usb: r8a66597-hcd: fix buffer overflow on odd-length FIFO reads
From: John Paul Adrian Glaubitz
Date: Sat Oct 03 2026 - 03:29:22 EST
Hi,
On Fri, 2026-10-02 at 23:32 +0200, Karl Mehltretter wrote:
> For an external R8A66597 (pdata->on_chip is false), the driver accesses
> the FIFO 16 bits at a time. It rounds an odd byte count up to the next
> word and passes that word count to ioread16_rep(), which stores both bytes
> of every word in the caller's buffer. The final word therefore writes one
> byte beyond an odd-length read, past the end of the buffer when the read
> fills it.
>
> This is visible while enumerating a USB device on an SH7785LCR. The USB
> core allocates nine bytes for the configuration descriptor header, and
> the controller driver stores ten bytes in it. SLUB reports the first
> redzone byte changing from 0xcc to 0x09 in usb_get_configuration().
> Odd-sized HID report descriptors trigger the same overwrite.
>
> Section 2.8.5 of the R8A66597 datasheet requires software to discard the
> excess byte after a 16-bit FIFO read when DTLN is odd. Read the trailing
> byte through a temporary word and copy only that byte.
>
> Fixes: 5d3043586db4 ("USB: r8a66597-hcd: host controller driver for R8A66597")
> Cc: stable@xxxxxxxxxxxxxxx
> Reported-by: John Paul Adrian Glaubitz <glaubitz@xxxxxxxxxxxxxxxxxxx>
> Link: https://lore.kernel.org/all/3bd32eaf159db61ed1d423e1d52a869b3689c682.camel@xxxxxxxxxxxxxxxxxxx/
> Assisted-by: LLM
> Signed-off-by: Karl Mehltretter <kmehltretter@xxxxxxxxx>
> ---
>
> Reproduced with 32-bit and 29-bit SH7785LCR kernels against a local
> R8A66597 QEMU model. Before this patch, slub_debug=FZPU reports overflows
> for the 9-byte configuration header and the 63-byte HID report descriptor.
> An A/B test of this patch with the 32-bit kernel enumerates the keyboard
> and removes both reports.
> Testing the fix on real hardware is welcome.
>
> drivers/usb/host/r8a66597.h | 11 +++++++++--
> 1 file changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/usb/host/r8a66597.h b/drivers/usb/host/r8a66597.h
> --- a/drivers/usb/host/r8a66597.h
> +++ b/drivers/usb/host/r8a66597.h
> @@ -178,8 +178,15 @@ static inline void r8a66597_read_fifo(struct r8a66597 *r8a66597,
> len & 0x03);
> }
> } else {
> - len = (len + 1) / 2;
> - ioread16_rep(fifoaddr, buf, len);
> + count = len / 2;
> + ioread16_rep(fifoaddr, buf, count);
> +
> + if (len & 0x00000001) {
> + u16 tmp;
> +
> + ioread16_rep(fifoaddr, &tmp, 1);
> + memcpy((unsigned char *)buf + count * 2, &tmp, 1);
> + }
> }
> }
>
Without the patch, the following memory leaks are reported:
[ 9.676000] [kmalloc Redzone overwritten] 0x820c4229-0x820c4229 @offset=553. First byte 0x9 instead of 0xcc
[ 9.676000] =============================================================================
[ 9.676000] BUG kmalloc-32 (Not tainted): Object corrupt
[ 9.676000] -----------------------------------------------------------------------------
[ 9.676000]
[ 9.676000] Allocated in usb_get_configuration+0x12c/0x11d8 age=51 cpu=0 pid=10
[ 9.676000] _raw_spin_lock_irqsave+0x20/0x38
[ 9.676000] ___slab_alloc+0x21e/0x44c
[ 9.676000] _raw_spin_unlock_irqrestore+0xe/0x44
[ 9.676000] __alloc_object+0xaa/0x19c
[ 9.676000] memset+0x0/0x8c
[ 9.676000] __kmalloc_noprof+0xb0/0x1c0
[ 9.676000] memset+0x0/0x8c
[ 9.676000] _kzalloc_noprof.constprop.0+0xc/0x1c
[ 9.676000] usb_get_configuration+0x12c/0x11d8
[ 9.676000] usb_get_configuration+0x12c/0x11d8
[ 9.676000] _kzalloc_noprof.constprop.0+0x0/0x1c
[ 9.676000] set_next_task_fair+0x190/0x350
[ 9.676000] __schedule+0x5aa/0x6bc
[ 9.676000] _raw_spin_lock_irqsave+0x20/0x38
[ 9.676000] _raw_spin_unlock_irqrestore+0xe/0x44
[ 9.676000] __try_to_del_timer_sync+0x4a/0x88
[ 9.676000] Slab 0x9ff41880 objects=32 used=6 fp=0x820c4320 flags=0x40000200(workingset|section=16|zone=0)
[ 9.676000] Object 0x820c4220 @offset=544 fp=0x820c42a0
[ 9.676000]
[ 9.676000] Redzone 820c4200: cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc ................
[ 9.676000] Redzone 820c4210: cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc ................
[ 9.676000] Object 820c4220: 09 02 20 00 01 01 00 80 fa 09 cc cc cc cc cc cc .. .............
[ 9.676000] Object 820c4230: cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc ................
[ 9.676000] Redzone 820c4240: cc cc cc cc ....
[ 9.676000] Padding 820c4274: 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a ZZZZZZZZZZZZ
[ 9.676000] Disabling lock debugging due to kernel taint
[ 9.676000] ------------[ cut here ]------------
[ 9.676000] WARNING: mm/slub.c:1257 at object_err+0x46/0x158, CPU#0: kworker/0:1/10
[ 9.676000] Modules linked in:
[ 9.676000]
[ 9.676000] CPU: 0 UID: 0 PID: 10 Comm: kworker/0:1 Tainted: G B 7.3.0-rc5-00340-ge767a4ea70a3 #6 PREEMPT
[ 9.676000] Tainted: [B]=BAD_PAGE
[ 9.676000] Workqueue: usb_hub_wq hub_event
[ 9.676000] PC is at object_err+0x46/0x158
[ 9.676000] PR is at object_err+0x46/0x158
[ 9.676000] PC : 80004e3a SP : 810cdc20 SR : 400081f1 TEA : c00d0008
[ 9.676000] R0 : 00000020 R1 : 8074959c R2 : 00000000 R3 : 00000020
[ 9.676000] R4 : 00000001 R5 : ff623224 R6 : 00000000 R7 : 00000000
[ 9.676000] R8 : 810023e0 R9 : 820c4220 R10 : 00000054 R11 : 80004d48
[ 9.676000] R12 : 0000808f R13 : 80004bd4 R14 : 810cdc20
[ 9.676000] MACH: 00000043 MACL: 0002bfa8 GBR : 2958a4c0 PR : 80004e3a
[ 9.676000]
[ 9.676000] Call trace:
[ 9.676000] [<800ff726>] check_bytes_and_report+0xa2/0xfc
[ 9.676000] [<800ff826>] check_object+0xa6/0x204
[ 9.676000] [<800ff684>] check_bytes_and_report+0x0/0xfc
[ 9.676000] [<80100276>] free_to_partial_list+0x9a/0x2b8
[ 9.676000] [<800788ce>] __timer_delete_sync+0x2a/0x50
[ 9.676000] [<80078804>] __try_to_del_timer_sync+0x0/0x88
[ 9.676000] [<80078900>] timer_delete_sync+0xc/0x18
[ 9.676000] [<801004de>] __slab_free+0x4a/0x19c
[ 9.676000] [<80009264>] _dev_notice+0x0/0x5c
[ 9.676000] [<8032b626>] usb_get_configuration+0x1a2/0x11d8
[ 9.676000] [<80112d6c>] delete_object_full+0x40/0x68
[ 9.676000] [<80101c4a>] kfree+0x112/0x1a4
[ 9.676000] [<80009264>] _dev_notice+0x0/0x5c
[ 9.676000] [<8032b626>] usb_get_configuration+0x1a2/0x11d8
[ 9.676000] [<8032b626>] usb_get_configuration+0x1a2/0x11d8
[ 9.676000] [<8032b626>] usb_get_configuration+0x1a2/0x11d8
[ 9.676000] [<80009264>] _dev_notice+0x0/0x5c
[ 9.676000] [<80044eb4>] set_next_task_fair+0x190/0x350
[ 9.676000] [<800788ce>] __timer_delete_sync+0x2a/0x50
[ 9.676000] [<80078804>] __try_to_del_timer_sync+0x0/0x88
[ 9.676000] [<80078900>] timer_delete_sync+0xc/0x18
[ 9.676000] [<804931f0>] schedule_timeout+0x98/0xe4
[ 9.676000] [<80323952>] usb_new_device+0x46/0x2ac
[ 9.676000] [<80493294>] schedule_timeout_uninterruptible+0x14/0x20
[ 9.676000] [<803249d0>] hub_event+0xbf0/0xdf4
[ 9.676000] [<8025667c>] _find_next_zero_bit+0x0/0x6c
[ 9.676000] [<80323470>] hub_init_func3+0x10/0x20
[ 9.676000] [<8002f078>] process_scheduled_works+0x148/0x25c
[ 9.676000] [<8003062c>] wq_worker_sleeping+0x14/0x88
[ 9.676000] [<8002ccbe>] assign_work+0x6c/0x82
[ 9.676000] [<8002f34c>] worker_thread+0xe4/0x1a8
[ 9.676000] [<80493e18>] _raw_spin_lock_irq+0x0/0x34
[ 9.676000] [<8002cc52>] assign_work+0x0/0x82
[ 9.676000] [<8003615c>] kthread+0xdc/0x114
[ 9.676000] [<8002f268>] worker_thread+0x0/0x1a8
[ 9.676000] [<8001d45c>] do_exit+0x0/0x798
[ 9.676000] [<80010200>] ret_from_kernel_thread+0xc/0x14
[ 9.676000] [<8003f0b8>] schedule_tail+0x0/0x78
[ 9.676000] [<80036080>] kthread+0x0/0x114
[ 9.676000]
[ 9.676000] ---[ end trace 0000000000000000 ]---
[ 9.676000] FIX kmalloc-32: Restoring kmalloc Redzone 0x820c4229-0x820c4229=0xcc
[ 9.676000] FIX kmalloc-32: Object at 0x820c4220 not freed
[ 10.596000] kmemleak: Kernel memory leak detector initialized (mem pool available: 15907)
[ 10.608000] kmemleak: Automatic memory scanning thread started
With the patch applied, there are no memory leaks reported during boot:
[ 10.236000] kmemleak: Kernel memory leak detector initialized (mem pool available: 15907)
[ 10.244000] kmemleak: Automatic memory scanning thread started
Tested-by: John Paul Adrian Glaubitz <glaubitz@xxxxxxxxxxxxxxxxxxx>
Adrian
--
.''`. John Paul Adrian Glaubitz
: :' : Debian Developer
`. `' Physicist
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