[PATCH] security:trusted_tpm2: Fix memory leak in tpm2_key_encode()

Line 36 (#1) allocates a memory chunk for scratch by kmalloc(), but
it is never freed through the function, which will lead to a memory
leak.

We should kfree() scratch before the function returns (#2, #3 and #4).

31 static int tpm2_key_encode(struct trusted_key_payload *payload,
32			   struct trusted_key_options *options,
33			   u8 *src, u32 len)
34 {
36	u8 *scratch = kmalloc(SCRATCH_SIZE, GFP_KERNEL);
      	// #1: kmalloc space
37	u8 *work = scratch, *work1;
50	if (!scratch)
51		return -ENOMEM;

56	if (options->blobauth_len == 0) {
60		if (WARN(IS_ERR(w), "BUG: Boolean failed to encode"))
61			return PTR_ERR(w); // #2: missing kfree
63	}

71	if (WARN(work - scratch + pub_len + priv_len + 14 > SCRATCH_SIZE,
72		 "BUG: scratch buffer is too small"))
73		return -EINVAL; // #3: missing kfree

  	// #4: missing kfree: scratch is never used afterwards.
82	if (WARN(IS_ERR(work1), "BUG: ASN.1 encoder failed"))
83		return PTR_ERR(work1);

85	return work1 - payload->blob;
86 }

Signed-off-by: Jianglei Nie <redacted>
---
 security/keys/trusted-keys/trusted_tpm2.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/security/keys/trusted-keys/trusted_tpm2.c b/security/keys/trusted-keys/trusted_tpm2.c
index 0165da386289..3408a74c855f 100644
--- a/security/keys/trusted-keys/trusted_tpm2.c
+++ b/security/keys/trusted-keys/trusted_tpm2.c

@@ -57,8 +57,10 @@ static int tpm2_key_encode(struct trusted_key_payload *payload,
 		unsigned char bool[3], *w = bool;
 		/* tag 0 is emptyAuth */
 		w = asn1_encode_boolean(w, w + sizeof(bool), true);
-		if (WARN(IS_ERR(w), "BUG: Boolean failed to encode"))
+		if (WARN(IS_ERR(w), "BUG: Boolean failed to encode")) {
+			kfree(scratch);
 			return PTR_ERR(w);
+		}
 		work = asn1_encode_tag(work, end_work, 0, bool, w - bool);
 	}
 

@@ -69,9 +71,12 @@ static int tpm2_key_encode(struct trusted_key_payload *payload,
 	 * trigger, so if it does there's something nefarious going on
 	 */
 	if (WARN(work - scratch + pub_len + priv_len + 14 > SCRATCH_SIZE,
-		 "BUG: scratch buffer is too small"))
+		 "BUG: scratch buffer is too small")) {
+		kfree(scratch);
 		return -EINVAL;
+	}
 
+	kfree(scratch);
 	work = asn1_encode_integer(work, end_work, options->keyhandle);
 	work = asn1_encode_octet_string(work, end_work, pub, pub_len);
 	work = asn1_encode_octet_string(work, end_work, priv, priv_len);

-- 
2.25.1

On Sun, Dec 12, 2021 at 09:54:03PM +0800, Jianglei Nie wrote:

Line 36 (#1) allocates a memory chunk for scratch by kmalloc(), but
it is never freed through the function, which will lead to a memory
leak.

We should kfree() scratch before the function returns (#2, #3 and #4).

31 static int tpm2_key_encode(struct trusted_key_payload *payload,
32			   struct trusted_key_options *options,
33			   u8 *src, u32 len)
34 {
36	u8 *scratch = kmalloc(SCRATCH_SIZE, GFP_KERNEL);
      	// #1: kmalloc space
37	u8 *work = scratch, *work1;
50	if (!scratch)
51		return -ENOMEM;

56	if (options->blobauth_len == 0) {
60		if (WARN(IS_ERR(w), "BUG: Boolean failed to encode"))
61			return PTR_ERR(w); // #2: missing kfree
63	}

71	if (WARN(work - scratch + pub_len + priv_len + 14 > SCRATCH_SIZE,
72		 "BUG: scratch buffer is too small"))
73		return -EINVAL; // #3: missing kfree

  	// #4: missing kfree: scratch is never used afterwards.
82	if (WARN(IS_ERR(work1), "BUG: ASN.1 encoder failed"))
83		return PTR_ERR(work1);

85	return work1 - payload->blob;
86 }

Signed-off-by: Jianglei Nie <redacted>

I don't know that we need to keep the line by line recap in
the full git log, but it def looks correct:

Reviewed-by: Serge Hallyn <serge@hallyn.com>

thanks,
-serge

On Sun, Dec 12, 2021 at 09:54:03PM +0800, Jianglei Nie wrote:

Line 36 (#1) allocates a memory chunk for scratch by kmalloc(), but
it is never freed through the function, which will lead to a memory
leak.

through the function => in the implementation

Also, "line 36" is a relative to something, right? What is it?

/Jarkko