sound/usb: out-of-bounds in prepare_playback_urb()

This is a bug report, not a patch submission.

We found a bug reachable in:

    path    sound/usb/endpoint.c` (the overwrite) and `sound/usb
    crash   out-of-bounds in prepare_playback_urb()
    commit  2f1baf1fc892 ("Merge tag 'trace-v7.2-rc7' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace")

Config, environment, the sanitizer report and a C reproducer follow.

== Notes ===============================================================
If you fix this bug, this tag credits the report and lets us close it on our side:

Everything in this mail is validated by the reproducer below.

We also hold an unreviewed LLM-generated analysis and candidate patch. The same reproducer panics the unpatched kernel and runs clean with that patch applied. Use it as a starting point, or ignore it and write your own:

patch.diff https://bugs.sh/b/8eacd4fa193b1b28/patch.diff
report.md https://bugs.sh/b/8eacd4fa193b1b28/report.md

A guide to taking it from here to a sendable patch, including the trailers to add: https://bugs.sh/patch.html

Happy to test patches. Complaints and suggestions about our work are welcome at:

[email protected]

== Environment =========================================================

    Reproduced on  2f1baf1fc892 ("Merge tag 'trace-v7.2-rc7' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace")
    VM setup       https://bugs.sh/b/8eacd4fa193b1b28/run.sh
    config         https://bugs.sh/b/8eacd4fa193b1b28/config.gz
    poc            https://bugs.sh/b/8eacd4fa193b1b28/repro.c

== Sanitizer Report ====================================================

BUG: KASAN: slab-out-of-bounds in prepare_playback_urb (sound/usb/pcm.c:1560)
Write of size 4 at addr ffff88801e696ad0 by task vhci_rx/178
CPU: 1 UID: 0 PID: 178 Comm: vhci_rx Not tainted 7.2.0-rc7+ #15 PREEMPT(lazy)
Call Trace:
dump_stack_lvl (lib/dump_stack.c:94 lib/dump_stack.c:120)
print_report (mm/kasan/report.c:378 mm/kasan/report.c:482)

kasan_report (mm/kasan/report.c:595)
prepare_playback_urb (sound/usb/pcm.c:1560)
prepare_outbound_urb (sound/usb/endpoint.c:340)
snd_usb_queue_pending_output_urbs (sound/usb/endpoint.c:501)
snd_complete_urb (sound/usb/endpoint.c:1834 sound/usb/endpoint.c:269 sound/usb/endpoint.c:587)
__usb_hcd_giveback_urb (drivers/usb/core/hcd.c:1657)
usb_hcd_giveback_urb (drivers/usb/core/hcd.c:1741)
vhci_rx_loop (drivers/usb/usbip/vhci_rx.c:107 (discriminator 1) drivers/usb/usbip/vhci_rx.c:242 (discriminator 1) drivers/usb/usbip/vhci_rx.c:265 (discriminator 1)) kthread (kernel/kthread.c:436)
ret_from_fork (arch/x86/kernel/process.c:158)
ret_from_fork_asm (arch/x86/entry/entry_64.S:245)

Allocated by task 174:
The buggy address belongs to the object at ffff88801e696a00
which belongs to the cache kmalloc-256 of size 256
The buggy address is located 0 bytes to the right of
allocated 208-byte region [ffff88801e696a00, ffff88801e696ad0)
The buggy address belongs to the physical page:
Memory state around the buggy address:
ffff88801e696980: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff88801e696a00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffff88801e696a80: 00 00 00 00 00 00 00 00 00 00 fc fc fc fc fc fc

^
ffff88801e696b00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff88801e696b80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc

---
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The suggested patch looks reasonable. Could you just submit it in a proper format for upstream (after verifying that the issue still happens in the latest upstream)?

thanks,

Takashi

Thanks for checking.
The patch has been tested on the latest upstream (tiwai/sound.git).

And I have checked related functionality and ensured the patch fixes the bug (to my knowledge):
https://lore.kernel.org/linux-sound/[email protected]/T/#u

Xiang