Subject: OVERFLOW_KUNIT_TEST fails with BUG: KASAN: stack-out-of-bounds in string_nocheck+0x168/0x1c8 (kernel 6.11-rc2, PowerMac G4 DP)

From: Erhard Furtner <[email-masked]>
Date: Fri, 9 Aug 2024 23:15:37 +0200

Greetings!

When KASAN is enabled the Overflow KUnit test fails:

[...]
    ok 16 shift_nonsense_test
    # overflow_allocation_test: 11 allocation overflow tests finished
==================================================================
BUG: KASAN: stack-out-of-bounds in string_nocheck+0x168/0x1c8
Read of size 1 at addr c976be40 by task kunit_try_catch/1843

CPU: 0 UID: 0 PID: 1843 Comm: kunit_try_catch Tainted: G                 N 6.11.0-rc2-PMacG4 #1
Tainted: [N]=TEST
Hardware name: PowerMac3,6 7455 0x80010303 PowerMac
Call Trace:
[c992fb80] [c16651c0] dump_stack_lvl+0x80/0xac (unreliable)
[c992fba0] [c04e0420] print_report+0xdc/0x504
[c992fc00] [c04e01d8] kasan_report+0xf8/0x108
[c992fc80] [c16ae4c8] string_nocheck+0x168/0x1c8
[c992fcf0] [c16b37a4] string+0xa8/0xbc
[c992fd60] [c16b8134] vsnprintf+0x868/0x1750
[c992fdf0] [c0b8490c] kvasprintf+0xa4/0x13c
[c992fe60] [c0b84c3c] kasprintf+0xb4/0xc8
[c992fed0] [c0f4c954] module_remove_driver+0x1f0/0x2fc
[c992ff00] [c0f21628] bus_remove_driver+0x1d0/0x240
[c992ff30] [bfd0cd40] kunit_put_resource+0x128/0x134 [kunit]
[c992ff50] [bfd0a120] kunit_cleanup+0x140/0x144 [kunit]
[c992ff90] [bfd10d64] kunit_generic_run_threadfn_adapter+0xf8/0x148 [kunit]
[c992ffc0] [c00f57e0] kthread+0x36c/0x37c
[c992fff0] [c0028304] start_kernel_thread+0x10/0x14

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:00000000 index:0x0 pfn:0x976b
flags: 0x0(zone=0)
raw: 00000000 00000000 eef2bb10 00000000 00000000 00000000 ffffffff 00000000
raw: 00000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 c976bd00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 c976bd80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>c976be00: 00 00 00 00 00 00 00 00 f1 f1 f1 f1 04 f2 04 f2
                                   ^
 c976be80: 00 04 f3 f3 00 00 00 00 00 00 00 00 00 00 00 00
 c976bf00: 00 00 f1 f1 f1 f1 00 f3 f3 f3 00 00 00 00 00 00
==================================================================
Disabling lock debugging due to kernel taint
    not ok 17 overflow_allocation_test
    # overflow_size_helpers_test: 43 overflow size helper tests finished
    ok 18 overflow_size_helpers_test
    # overflows_type_test: 378 overflows_type() tests finished
    ok 19 overflows_type_test
    # same_type_test: 0 __same_type() tests finished
    ok 20 same_type_test
    # castable_to_type_test: 75 castable_to_type() tests finished
    ok 21 castable_to_type_test
    ok 22 DEFINE_FLEX_test
# overflow: pass:21 fail:1 skip:0 total:22
# Totals: pass:21 fail:1 skip:0 total:22
not ok 1 overflow

This is reproducible on my machine and always happens when running the test via 'modprobe -v overflow_kunit'. Without KASAN enabled (but KFENCE) overflow_allocation_test passes.

Kernel .config and full dmesg attached.

Regards,
Erhard