2022-03-21 22:16:52

by Tom Rix

Subject: [PATCH] livepatch: Reorder to use before freeing a pointer

From: Tom Rix <[email protected]>

Clang static analysis reports this issue
livepatch-shadow-fix1.c:113:2: warning: Use of
memory after it is freed
pr_info("%s: dummy @ %p, prevented leak @ %p\n",
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The pointer is freed in the previous statement.
Reorder the pr_info to report before the free.

Signed-off-by: Tom Rix <[email protected]>
---
samples/livepatch/livepatch-shadow-fix1.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/samples/livepatch/livepatch-shadow-fix1.c b/samples/livepatch/livepatch-shadow-fix1.c
index 918ce17b43fda..6701641bf12d4 100644
--- a/samples/livepatch/livepatch-shadow-fix1.c
+++ b/samples/livepatch/livepatch-shadow-fix1.c
@@ -109,9 +109,9 @@ static void livepatch_fix1_dummy_leak_dtor(void *obj, void *shadow_data)
void *d = obj;
int **shadow_leak = shadow_data;

- kfree(*shadow_leak);
pr_info("%s: dummy @ %p, prevented leak @ %p\n",
__func__, d, *shadow_leak);
+ kfree(*shadow_leak);
}

static void livepatch_fix1_dummy_free(struct dummy *d)
--
2.26.3

2022-03-21 23:12:45

by David Vernet

Subject: Re: [PATCH] livepatch: Reorder to use before freeing a pointer

On Sat, Mar 19, 2022 at 09:51:59AM -0700, [email protected] wrote:
> From: Tom Rix <[email protected]>
>
> Clang static analysis reports this issue
> livepatch-shadow-fix1.c:113:2: warning: Use of
> memory after it is freed
> pr_info("%s: dummy @ %p, prevented leak @ %p\n",
> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
> The pointer is freed in the previous statement.
> Reorder the pr_info to report before the free.
>
> Signed-off-by: Tom Rix <[email protected]>
> ---
> samples/livepatch/livepatch-shadow-fix1.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/samples/livepatch/livepatch-shadow-fix1.c b/samples/livepatch/livepatch-shadow-fix1.c
> index 918ce17b43fda..6701641bf12d4 100644
> --- a/samples/livepatch/livepatch-shadow-fix1.c
> +++ b/samples/livepatch/livepatch-shadow-fix1.c
> @@ -109,9 +109,9 @@ static void livepatch_fix1_dummy_leak_dtor(void *obj, void *shadow_data)
> void *d = obj;
> int **shadow_leak = shadow_data;
>
> - kfree(*shadow_leak);
> pr_info("%s: dummy @ %p, prevented leak @ %p\n",
> __func__, d, *shadow_leak);
> + kfree(*shadow_leak);
> }
>
> static void livepatch_fix1_dummy_free(struct dummy *d)
> --
> 2.26.3
>

The fix looks good, though it looks like there is also a similar
use-after-free in livepatch_fix2_dummy_leak_dtor() in
livepatch-shadow-fix2.c. Could you please also fix that as part of this
patch?

Thanks,
David