2019-05-20 07:15:47

by Pi-Hsun Shih

Subject: [PATCH] pstore: Set tfm to NULL on free_buf_for_compression.

Set tfm to NULL on free_buf_for_compression after crypto_free_comp.

This avoid a use-after-free when allocate_buf_for_compression and
free_buf_for_compression are called twice. Although
free_buf_for_compression freed the tfm, allocate_buf_for_compression
won't reinitialize the tfm since the tfm pointer is not NULL.

Fixes: 95047b0519c1 ("pstore: Refactor compression initialization")
Signed-off-by: Pi-Hsun Shih <[email protected]>
---
fs/pstore/platform.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/fs/pstore/platform.c b/fs/pstore/platform.c
index 75887a269b64..8355a46638d0 100644
--- a/fs/pstore/platform.c
+++ b/fs/pstore/platform.c
@@ -347,8 +347,10 @@ static void allocate_buf_for_compression(void)

static void free_buf_for_compression(void)
{
- if (IS_ENABLED(CONFIG_PSTORE_COMPRESS) && tfm)
+ if (IS_ENABLED(CONFIG_PSTORE_COMPRESS) && tfm) {
crypto_free_comp(tfm);
+ tfm = NULL;
+ }
kfree(big_oops_buf);
big_oops_buf = NULL;
big_oops_buf_sz = 0;
--
2.21.0.1020.gf2820cf01a-goog

2019-05-20 18:18:30

by Kees Cook

Subject: Re: [PATCH] pstore: Set tfm to NULL on free_buf_for_compression.

On Mon, May 20, 2019 at 02:51:19PM +0800, Pi-Hsun Shih wrote:
> Set tfm to NULL on free_buf_for_compression after crypto_free_comp.
>
> This avoid a use-after-free when allocate_buf_for_compression and
> free_buf_for_compression are called twice. Although
> free_buf_for_compression freed the tfm, allocate_buf_for_compression
> won't reinitialize the tfm since the tfm pointer is not NULL.
>
> Fixes: 95047b0519c1 ("pstore: Refactor compression initialization")
> Signed-off-by: Pi-Hsun Shih <[email protected]>

Thank you! Yes, without this, reloading pstore backend modules would
cause bad behavior. :)

Applied; will send to Linus shortly.

-Kees

> ---
> fs/pstore/platform.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/fs/pstore/platform.c b/fs/pstore/platform.c
> index 75887a269b64..8355a46638d0 100644
> --- a/fs/pstore/platform.c
> +++ b/fs/pstore/platform.c
> @@ -347,8 +347,10 @@ static void allocate_buf_for_compression(void)
>
> static void free_buf_for_compression(void)
> {
> - if (IS_ENABLED(CONFIG_PSTORE_COMPRESS) && tfm)
> + if (IS_ENABLED(CONFIG_PSTORE_COMPRESS) && tfm) {
> crypto_free_comp(tfm);
> + tfm = NULL;
> + }
> kfree(big_oops_buf);
> big_oops_buf = NULL;
> big_oops_buf_sz = 0;
> --
> 2.21.0.1020.gf2820cf01a-goog
>

--
Kees Cook