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

[Pi-Hsun Shih]

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 <pihsun@xxxxxxxxxxxx>
---
 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