[PATCH] kunit: string-stream: Fix a UAF bug in kunit_init_suite()

[Jinjie Ruan]

In kunit_debugfs_create_suite(), if alloc_string_stream() fails in the
kunit_suite_for_each_test_case() loop, the "suite->log = stream"
has assigned before, and the error path only free the suite->log's stream
memory but not set it to NULL in string_stream_destroy(), so the later
string_stream_clear() of suite->log in kunit_init_suite() will cause
below UAF bug.

Set stream pointer to NULL after free in string_stream_destroy()
to fix it.

Unable to handle kernel paging request at virtual address 006440150000030d
Mem abort info:
ESR = 0x0000000096000004
EC = 0x25: DABT (current EL), IL = 32 bits
SET = 0, FnV = 0
EA = 0, S1PTW = 0
FSC = 0x04: level 0 translation fault
Data abort info:
ISV = 0, ISS = 0x00000004, ISS2 = 0x00000000
CM = 0, WnR = 0, TnD = 0, TagAccess = 0
GCS = 0, Overlay = 0, DirtyBit = 0, Xs = 0
[006440150000030d] address between user and kernel address ranges
Internal error: Oops: 0000000096000004 [#1] PREEMPT SMP
Dumping ftrace buffer:
(ftrace buffer empty)
Modules linked in: iio_test_gts industrialio_gts_helper cfg80211 rfkill ipv6 [last unloaded: iio_test_gts]
CPU: 5 UID: 0 PID: 6253 Comm: modprobe Tainted: G B W N 6.12.0-rc4+ #458
Tainted: [B]=BAD_PAGE, [W]=WARN, [N]=TEST
Hardware name: linux,dummy-virt (DT)
pstate: 40000005 (nZcv daif -PAN -UAO -TCO -DIT -SSBS BTYPE=--)
pc : string_stream_clear+0x54/0x1ac
lr : string_stream_clear+0x1a8/0x1ac
sp : ffffffc080b47410
x29: ffffffc080b47410 x28: 006440550000030d x27: ffffff80c96b5e98
x26: ffffff80c96b5e80 x25: ffffffe461b3f6c0 x24: 0000000000000003
x23: ffffff80c96b5e88 x22: 1ffffff019cdf4fc x21: dfffffc000000000
x20: ffffff80ce6fa7e0 x19: 032202a80000186d x18: 0000000000001840
x17: 0000000000000000 x16: 0000000000000000 x15: ffffffe45c355cb4
x14: ffffffe45c35589c x13: ffffffe45c03da78 x12: ffffffb810168e75
x11: 1ffffff810168e74 x10: ffffffb810168e74 x9 : dfffffc000000000
x8 : 0000000000000004 x7 : 0000000000000003 x6 : 0000000000000001
x5 : ffffffc080b473a0 x4 : 0000000000000000 x3 : 0000000000000000
x2 : 0000000000000001 x1 : ffffffe462fbf620 x0 : dfffffc000000000
Call trace:
string_stream_clear+0x54/0x1ac
__kunit_test_suites_init+0x108/0x1d8
kunit_exec_run_tests+0xb8/0x100
kunit_module_notify+0x400/0x55c
notifier_call_chain+0xfc/0x3b4
blocking_notifier_call_chain+0x68/0x9c
do_init_module+0x24c/0x5c8
load_module+0x4acc/0x4e90
init_module_from_file+0xd4/0x128
idempotent_init_module+0x2d4/0x57c
__arm64_sys_finit_module+0xac/0x100
invoke_syscall+0x6c/0x258
el0_svc_common.constprop.0+0x160/0x22c
do_el0_svc+0x44/0x5c
el0_svc+0x48/0xb8
el0t_64_sync_handler+0x13c/0x158
el0t_64_sync+0x190/0x194
Code: f9400753 d2dff800 f2fbffe0 d343fe7c (38e06b80)
---[ end trace 0000000000000000 ]---
Kernel panic - not syncing: Oops: Fatal exception

Cc: sta...@vger.kernel.org
Fixes: a3fdf784780c ("kunit: string-stream: Decouple string_stream from kunit")
Signed-off-by: Jinjie Ruan <ruanj...@huawei.com>
---
lib/kunit/string-stream.c | 1 +
1 file changed, 1 insertion(+)

diff --git a/lib/kunit/string-stream.c b/lib/kunit/string-stream.c
index 54f4fdcbfac8..00ad518b730b 100644
--- a/lib/kunit/string-stream.c
+++ b/lib/kunit/string-stream.c
@@ -178,6 +178,7 @@ void string_stream_destroy(struct string_stream *stream)

string_stream_clear(stream);
kfree(stream);
+ stream = NULL;
}

static void resource_free_string_stream(void *p)
--
2.34.1

[Jinjie Ruan]

Gentle Ping.

[David Gow]

Nice catch, thanks.

Reviewed-by: David Gow <davi...@google.com>

Cheers,
-- David

[Kuan-Wei Chiu]

Hi Jinjie,

Thanks for proposing the fix. However, I don't believe it fully
resolves the UAF issue. Changing the stream pointer value within
string_stream_destroy() doesn't update the caller's stream pointer, so
the issue remains.

I think the correct approach would be to set the log pointer to NULL in
the error path of kunit_debugfs_create_suite() to address the issue.
Let me know if I've missed something or overlooked an obvious detail.

Here's the proposed code:

diff --git a/lib/kunit/debugfs.c b/lib/kunit/debugfs.c
index d548750a325a..b25d214b93e1 100644
--- a/lib/kunit/debugfs.c
+++ b/lib/kunit/debugfs.c
@@ -212,8 +212,11 @@ void kunit_debugfs_create_suite(struct kunit_suite *suite)

err:
string_stream_destroy(suite->log);
- kunit_suite_for_each_test_case(suite, test_case)
+ suite->log = NULL;
+ kunit_suite_for_each_test_case(suite, test_case) {
string_stream_destroy(test_case->log);
+ test_case->log = NULL;
+ }
}

void kunit_debugfs_destroy_suite(struct kunit_suite *suite)

[Kuan-Wei Chiu]

BTW, since alloc_string_stream() returns -ENOMEM on error rather than
NULL, it's best for the caller to check it with IS_ERR() instead of
IS_ERR_OR_NULL(). It's not a big issue, but I can send a cleanup patch
later to address this.

Regards,
Kuan-Wei

[Jinjie Ruan]

Yes, I also notice it, but It's not a big issue. Thank you very much!

>
> Regards,
> Kuan-Wei

[Jinjie Ruan]

It looks fine, test it and if ok, will update it.

[Jinjie Ruan]

In kunit_debugfs_create_suite(), if alloc_string_stream() fails in the
kunit_suite_for_each_test_case() loop, the "suite->log = stream"
has assigned before, and the error path only free the suite->log's stream

memory but not set it to NULL, so the later string_stream_clear() of

suite->log in kunit_init_suite() will cause below UAF bug.

Set stream pointer to NULL after free to fix it.

Suggested-by: Kuan-Wei Chiu <visit...@gmail.com>

Signed-off-by: Jinjie Ruan <ruanj...@huawei.com>
---

v2:
- Correct the fix way.
- Add Suggested-by.
---
lib/kunit/debugfs.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/lib/kunit/debugfs.c b/lib/kunit/debugfs.c
index d548750a325a..b25d214b93e1 100644
--- a/lib/kunit/debugfs.c
+++ b/lib/kunit/debugfs.c
@@ -212,8 +212,11 @@ void kunit_debugfs_create_suite(struct kunit_suite *suite)

err:
string_stream_destroy(suite->log);
- kunit_suite_for_each_test_case(suite, test_case)
+ suite->log = NULL;
+ kunit_suite_for_each_test_case(suite, test_case) {
string_stream_destroy(test_case->log);
+ test_case->log = NULL;
+ }
}

void kunit_debugfs_destroy_suite(struct kunit_suite *suite)
--
2.34.1

[Kuan-Wei Chiu]

Reviewed-by: Kuan-Wei Chiu <visit...@gmail.com>

Regards,
Kuan-Wei

[David Gow]

Sorry, I missed this version.
It looks good to me.

Reviewed-by: David Gow <davi...@google.com>

Cheers,
-- David

> lib/kunit/debugfs.c | 5 ++++-
> 1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/lib/kunit/debugfs.c b/lib/kunit/debugfs.c
> index d548750a325a..b25d214b93e1 100644
> --- a/lib/kunit/debugfs.c
> +++ b/lib/kunit/debugfs.c
> @@ -212,8 +212,11 @@ void kunit_debugfs_create_suite(struct kunit_suite *suite)
>
> err:
> string_stream_destroy(suite->log);
> - kunit_suite_for_each_test_case(suite, test_case)
> + suite->log = NULL;
> + kunit_suite_for_each_test_case(suite, test_case) {
> string_stream_destroy(test_case->log);
> + test_case->log = NULL;
> + }
> }
>
> void kunit_debugfs_destroy_suite(struct kunit_suite *suite)
> --
> 2.34.1
>

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[Kuan-Wei Chiu]

On Tue, Nov 12, 2024 at 04:03:14PM +0800, Jinjie Ruan wrote:

> In kunit_debugfs_create_suite(), if alloc_string_stream() fails in the
> kunit_suite_for_each_test_case() loop, the "suite->log = stream"
> has assigned before, and the error path only free the suite->log's stream
> memory but not set it to NULL, so the later string_stream_clear() of
> suite->log in kunit_init_suite() will cause below UAF bug.
>
> Set stream pointer to NULL after free to fix it.

I just noticed that since v2, we no longer set the stream pointer to
NULL but instead set suite->log to NULL. This description needs a
slight adjustment.

Regards,
Kuan-Wei