[PATCH] KEYS: trusted: Reject short TPM2 public areas

[PATCH] KEYS: trusted: Reject short TPM2 public areas

[Daehyeon Ko]

tpm2_load_cmd() reads TPMA_OBJECT with get_unaligned_be32(pub + 4), but
does not require public_len to cover that field.

A new-format blob with public_len zero makes the read begin at the end of
the B + 4-byte decoded allocation, causing a four-byte heap out-of-bounds
read before the TPM command is transmitted. This is reachable from an
unprivileged add_key() call when TPM trusted keys and a TPM2 device are
available.

This affects v5.13-rc1 and later kernels built with CONFIG_TRUSTED_KEYS=y
and CONFIG_TRUSTED_KEYS_TPM=y when a TPM2 device is present. A KASAN run
as UID 1000 with no effective capabilities reported:

BUG: KASAN: slab-out-of-bounds in tpm2_unseal_trusted
Read of size 4 at addr ffff888106273b48 by task exploit/160
CPU: 1 UID: 1000 PID: 160 Comm: exploit
The buggy address belongs to the object at ffff888106273b40
 which belongs to the cache kmalloc-8 of size 8
The buggy address is located 0 bytes to the right of
 allocated 8-byte region [ffff888106273b40, ffff888106273b48)

TPMT_PUBLIC starts with the two-byte type, two-byte nameAlg and four-byte
objectAttributes fields. Require public_len to cover all eight bytes before
reading the attributes.

The exact input produced the KASAN read in 3/3 fresh boots. The fixed build
rejected it with -E2BIG and no KASAN report in 3/3 boots; valid new- and
old-format trusted-key loads continued to succeed.

Fixes: e5fb5d2c5a03 ("security: keys: trusted: Make sealed key properly interoperable")
Cc: stable@vger.kernel.org
Assisted-by: LLM
Signed-off-by: Daehyeon Ko <4ncienth@gmail.com>
---
Tested with QEMU tpm-tis and swtpm: vulnerable 3/3 KASAN reports,
fixed 3/3 clean -E2BIG rejections, with public_len 7/8 and new/old-format
controls passing. Stable 5.15+ requires 114f00d738f1 first; both patches
apply cleanly in that order.

The source reproducer and full logs are available privately on request.

 security/keys/trusted-keys/trusted_tpm2.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/security/keys/trusted-keys/trusted_tpm2.c b/security/keys/trusted-keys/trusted_tpm2.c
index c2a69bcf381d7..b3109e0a924f5 100644
--- a/security/keys/trusted-keys/trusted_tpm2.c
+++ b/security/keys/trusted-keys/trusted_tpm2.c
@@ -418,6 +418,8 @@ static int tpm2_load_cmd(struct tpm_chip *chip,
 	public_len = get_unaligned_be16(blob + 2 + private_len);
 	if (private_len + 2 + public_len + 2 > blob_len)
 		return -E2BIG;
+	if (public_len < 8)
+		return -E2BIG;
 
 	pub = blob + 2 + private_len + 2;
 	/* key attributes are always at offset 4 */

base-commit: 27d14d3b15d5691bcbf0683883a2ea12469edbea

Re: [PATCH] KEYS: trusted: Reject short TPM2 public areas

[sashiko-bot]

> tpm2_load_cmd() reads TPMA_OBJECT with get_unaligned_be32(pub + 4), but
> does not require public_len to cover that field.
> 
> A new-format blob with public_len zero makes the read begin at the end of
> the B + 4-byte decoded allocation, causing a four-byte heap out-of-bounds
> read before the TPM command is transmitted. This is reachable from an
> unprivileged add_key() call when TPM trusted keys and a TPM2 device are
> available.
> 
> This affects v5.13-rc1 and later kernels built with CONFIG_TRUSTED_KEYS=y
> and CONFIG_TRUSTED_KEYS_TPM=y when a TPM2 device is present. A KASAN run
> as UID 1000 with no effective capabilities reported:
> 
> BUG: KASAN: slab-out-of-bounds in tpm2_unseal_trusted
> Read of size 4 at addr ffff888106273b48 by task exploit/160
> [ ... ]
> 
> Fixes: e5fb5d2c5a03 ("security: keys: trusted: Make sealed key properly interoperable")
> Cc: stable@vger.kernel.org
> Assisted-by: LLM
> Signed-off-by: Daehyeon Ko <4ncienth@gmail.com>

Sashiko has reviewed this patch and found no issues. It looks great!

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260925095308.3248297-1-4ncienth@gmail.com?part=1

Re: [PATCH] KEYS: trusted: Reject short TPM2 public areas

[Jarkko Sakkinen]

On Fri, Sep 25, 2026 at 06:53:08PM +0900, Daehyeon Ko wrote:
> tpm2_load_cmd() reads TPMA_OBJECT with get_unaligned_be32(pub + 4), but
> does not require public_len to cover that field.
> 
> A new-format blob with public_len zero makes the read begin at the end of
> the B + 4-byte decoded allocation, causing a four-byte heap out-of-bounds
> read before the TPM command is transmitted. This is reachable from an
> unprivileged add_key() call when TPM trusted keys and a TPM2 device are
> available.
> 
> This affects v5.13-rc1 and later kernels built with CONFIG_TRUSTED_KEYS=y
> and CONFIG_TRUSTED_KEYS_TPM=y when a TPM2 device is present. A KASAN run
> as UID 1000 with no effective capabilities reported:
> 
> BUG: KASAN: slab-out-of-bounds in tpm2_unseal_trusted
> Read of size 4 at addr ffff888106273b48 by task exploit/160
> CPU: 1 UID: 1000 PID: 160 Comm: exploit
> The buggy address belongs to the object at ffff888106273b40
>  which belongs to the cache kmalloc-8 of size 8
> The buggy address is located 0 bytes to the right of
>  allocated 8-byte region [ffff888106273b40, ffff888106273b48)
> 
> TPMT_PUBLIC starts with the two-byte type, two-byte nameAlg and four-byte
> objectAttributes fields. Require public_len to cover all eight bytes before
> reading the attributes.
> 
> The exact input produced the KASAN read in 3/3 fresh boots. The fixed build
> rejected it with -E2BIG and no KASAN report in 3/3 boots; valid new- and
> old-format trusted-key loads continued to succeed.
> 
> Fixes: e5fb5d2c5a03 ("security: keys: trusted: Make sealed key properly interoperable")
> Cc: stable@vger.kernel.org
> Assisted-by: LLM
> Signed-off-by: Daehyeon Ko <4ncienth@gmail.com>
> ---
> Tested with QEMU tpm-tis and swtpm: vulnerable 3/3 KASAN reports,
> fixed 3/3 clean -E2BIG rejections, with public_len 7/8 and new/old-format
> controls passing. Stable 5.15+ requires 114f00d738f1 first; both patches
> apply cleanly in that order.
> 
> The source reproducer and full logs are available privately on request.
> 
>  security/keys/trusted-keys/trusted_tpm2.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/security/keys/trusted-keys/trusted_tpm2.c b/security/keys/trusted-keys/trusted_tpm2.c
> index c2a69bcf381d7..b3109e0a924f5 100644
> --- a/security/keys/trusted-keys/trusted_tpm2.c
> +++ b/security/keys/trusted-keys/trusted_tpm2.c
> @@ -418,6 +418,8 @@ static int tpm2_load_cmd(struct tpm_chip *chip,
>  	public_len = get_unaligned_be16(blob + 2 + private_len);
>  	if (private_len + 2 + public_len + 2 > blob_len)
>  		return -E2BIG;
> +	if (public_len < 8)
> +		return -E2BIG;
>  
>  	pub = blob + 2 + private_len + 2;
>  	/* key attributes are always at offset 4 */
> 
> base-commit: 27d14d3b15d5691bcbf0683883a2ea12469edbea

Yeah, makes sense as those eight bytes is what covers the data needed
to identify the key.


Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>

Thanks.

Br, Jarkko

Re: [PATCH] KEYS: trusted: Reject short TPM2 public areas

[Jarkko Sakkinen]

On Fri, Sep 25, 2026 at 06:53:08PM +0900, Daehyeon Ko wrote:
> tpm2_load_cmd() reads TPMA_OBJECT with get_unaligned_be32(pub + 4), but
> does not require public_len to cover that field.
> 
> A new-format blob with public_len zero makes the read begin at the end of

New-format is not anything. TPM2 protocol format might be better here (nit).

> the B + 4-byte decoded allocation, causing a four-byte heap out-of-bounds
> read before the TPM command is transmitted. This is reachable from an
> unprivileged add_key() call when TPM trusted keys and a TPM2 device are
> available.
> 
> This affects v5.13-rc1 and later kernels built with CONFIG_TRUSTED_KEYS=y
> and CONFIG_TRUSTED_KEYS_TPM=y when a TPM2 device is present. A KASAN run
> as UID 1000 with no effective capabilities reported:
> 
> BUG: KASAN: slab-out-of-bounds in tpm2_unseal_trusted
> Read of size 4 at addr ffff888106273b48 by task exploit/160
> CPU: 1 UID: 1000 PID: 160 Comm: exploit
> The buggy address belongs to the object at ffff888106273b40
>  which belongs to the cache kmalloc-8 of size 8
> The buggy address is located 0 bytes to the right of
>  allocated 8-byte region [ffff888106273b40, ffff888106273b48)
> 
> TPMT_PUBLIC starts with the two-byte type, two-byte nameAlg and four-byte
> objectAttributes fields. Require public_len to cover all eight bytes before
> reading the attributes.
> 
> The exact input produced the KASAN read in 3/3 fresh boots. The fixed build
> rejected it with -E2BIG and no KASAN report in 3/3 boots; valid new- and
> old-format trusted-key loads continued to succeed.
> 
> Fixes: e5fb5d2c5a03 ("security: keys: trusted: Make sealed key properly interoperable")
> Cc: stable@vger.kernel.org
> Assisted-by: LLM
> Signed-off-by: Daehyeon Ko <4ncienth@gmail.com>
> ---
> Tested with QEMU tpm-tis and swtpm: vulnerable 3/3 KASAN reports,
> fixed 3/3 clean -E2BIG rejections, with public_len 7/8 and new/old-format
> controls passing. Stable 5.15+ requires 114f00d738f1 first; both patches
> apply cleanly in that order.
> 
> The source reproducer and full logs are available privately on request.
> 
>  security/keys/trusted-keys/trusted_tpm2.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/security/keys/trusted-keys/trusted_tpm2.c b/security/keys/trusted-keys/trusted_tpm2.c
> index c2a69bcf381d7..b3109e0a924f5 100644
> --- a/security/keys/trusted-keys/trusted_tpm2.c
> +++ b/security/keys/trusted-keys/trusted_tpm2.c
> @@ -418,6 +418,8 @@ static int tpm2_load_cmd(struct tpm_chip *chip,
>  	public_len = get_unaligned_be16(blob + 2 + private_len);
>  	if (private_len + 2 + public_len + 2 > blob_len)
>  		return -E2BIG;

I was writing summary of the changes for my v7.4-rc1 PR but this
does not look right.


This would really need an explanation like:

/* 
 * Check that TPMT_PUBLIC fields type, nameAlg and objectAttributes are covered
 * in order to avoid out-of-bounds read.
 */

> +	if (public_len < 8)
> +		return -E2BIG;

Why would you pick -E2BIG as I guess here that is not the problem?

Just checking before proposing anything.

>  
>  	pub = blob + 2 + private_len + 2;
>  	/* key attributes are always at offset 4 */
> 
> base-commit: 27d14d3b15d5691bcbf0683883a2ea12469edbea

I'll drop this patch and postpone v7.4-rc1 at least one day so there
is still time.

Br, Jarkko

[PATCH v2] KEYS: trusted: Reject short TPM2 public areas

[Daehyeon Ko]

tpm2_load_cmd() reads TPMA_OBJECT with get_unaligned_be32(pub + 4), but
does not require public_len to cover that field.

A TPM 2.0 ASN.1 key blob with public_len zero makes the read begin at the
end of the B + 4-byte decoded allocation, causing a four-byte heap
out-of-bounds read before the TPM command is transmitted. This is reachable
from an unprivileged add_key() call when TPM trusted keys and a TPM2 device
are available.

This affects v5.13-rc1 and later kernels built with CONFIG_TRUSTED_KEYS=y
and CONFIG_TRUSTED_KEYS_TPM=y when a TPM2 device is present. A KASAN run
as UID 1000 with no effective capabilities reported:

BUG: KASAN: slab-out-of-bounds in tpm2_unseal_trusted
Read of size 4 at addr ffff888106273b48 by task exploit/160
CPU: 1 UID: 1000 PID: 160 Comm: exploit
The buggy address belongs to the object at ffff888106273b40
 which belongs to the cache kmalloc-8 of size 8
The buggy address is located 0 bytes to the right of
 allocated 8-byte region [ffff888106273b40, ffff888106273b48)

TPMT_PUBLIC starts with the two-byte type, two-byte nameAlg and four-byte
objectAttributes fields. Require public_len to cover all eight bytes before
reading the attributes.

The exact input produced the KASAN read in 3/3 fresh boots. The fixed build
rejected it with -EINVAL and no KASAN report in 3/3 boots; valid TPM 2.0
ASN.1 and legacy trusted-key loads continued to succeed.

The issue was found with an LLM-assisted source audit and validated with an
end-to-end QEMU and swtpm reproducer.

Fixes: e5fb5d2c5a03 ("security: keys: trusted: Make sealed key properly interoperable")
Cc: stable@vger.kernel.org
Signed-off-by: Daehyeon Ko <4ncienth@gmail.com>
---
Changes in v2:
- Describe the wrapper as the TPM 2.0 ASN.1 key format.
- Explain the eight-byte minimum next to the check.
- Return -EINVAL for a malformed TPMT_PUBLIC instead of -E2BIG.
- Replace the obsolete Assisted-by trailer with changelog disclosure.

v1: https://lore.kernel.org/r/20260925095308.3248297-1-4ncienth@gmail.com

 security/keys/trusted-keys/trusted_tpm2.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/security/keys/trusted-keys/trusted_tpm2.c b/security/keys/trusted-keys/trusted_tpm2.c
index 30188a0ec6766..fb45795b53327 100644
--- a/security/keys/trusted-keys/trusted_tpm2.c
+++ b/security/keys/trusted-keys/trusted_tpm2.c
@@ -425,6 +425,13 @@ static int tpm2_load_cmd(struct tpm_chip *chip,
 	if (private_len + 2 + public_len + 2 > blob_len)
 		return -E2BIG;
 
+	/*
+	 * TPMT_PUBLIC starts with type (2), nameAlg (2), and
+	 * objectAttributes (4), which is read below.
+	 */
+	if (public_len < 8)
+		return -EINVAL;
+
 	pub = blob + 2 + private_len + 2;
 	/* key attributes are always at offset 4 */
 	attrs = get_unaligned_be32(pub + 4);

base-commit: 722658cac48a6ba49f5506fd74d010ad9dbb2f05
-- 
2.55.0

Re: [PATCH v2] KEYS: trusted: Reject short TPM2 public areas

[sashiko-bot]

> tpm2_load_cmd() reads TPMA_OBJECT with get_unaligned_be32(pub + 4), but
> does not require public_len to cover that field.
> 
> A TPM 2.0 ASN.1 key blob with public_len zero makes the read begin at the
> end of the B + 4-byte decoded allocation, causing a four-byte heap
> out-of-bounds read before the TPM command is transmitted. This is reachable
> from an unprivileged add_key() call when TPM trusted keys and a TPM2 device
> are available.
> 
> This affects v5.13-rc1 and later kernels built with CONFIG_TRUSTED_KEYS=y
> and CONFIG_TRUSTED_KEYS_TPM=y when a TPM2 device is present. A KASAN run
> as UID 1000 with no effective capabilities reported:
> 
> BUG: KASAN: slab-out-of-bounds in tpm2_unseal_trusted
> Read of size 4 at addr ffff888106273b48 by task exploit/160
> [ ... ]
> end-to-end QEMU and swtpm reproducer.
> 
> Fixes: e5fb5d2c5a03 ("security: keys: trusted: Make sealed key properly interoperable")
> Cc: stable@vger.kernel.org
> Signed-off-by: Daehyeon Ko <4ncienth@gmail.com>

Sashiko has reviewed this patch and found no issues.

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261020161954.3956212-1-4ncienth@gmail.com?part=1

Re: [PATCH v2] KEYS: trusted: Reject short TPM2 public areas

[Jarkko Sakkinen]

On Wed, Oct 21, 2026 at 01:19:54AM +0900, Daehyeon Ko wrote:
> tpm2_load_cmd() reads TPMA_OBJECT with get_unaligned_be32(pub + 4), but
> does not require public_len to cover that field.
> 
> A TPM 2.0 ASN.1 key blob with public_len zero makes the read begin at the
> end of the B + 4-byte decoded allocation, causing a four-byte heap
> out-of-bounds read before the TPM command is transmitted. This is reachable
> from an unprivileged add_key() call when TPM trusted keys and a TPM2 device
> are available.
> 
> This affects v5.13-rc1 and later kernels built with CONFIG_TRUSTED_KEYS=y
> and CONFIG_TRUSTED_KEYS_TPM=y when a TPM2 device is present. A KASAN run
> as UID 1000 with no effective capabilities reported:
> 
> BUG: KASAN: slab-out-of-bounds in tpm2_unseal_trusted
> Read of size 4 at addr ffff888106273b48 by task exploit/160
> CPU: 1 UID: 1000 PID: 160 Comm: exploit
> The buggy address belongs to the object at ffff888106273b40
>  which belongs to the cache kmalloc-8 of size 8
> The buggy address is located 0 bytes to the right of
>  allocated 8-byte region [ffff888106273b40, ffff888106273b48)
> 
> TPMT_PUBLIC starts with the two-byte type, two-byte nameAlg and four-byte
> objectAttributes fields. Require public_len to cover all eight bytes before
> reading the attributes.
> 
> The exact input produced the KASAN read in 3/3 fresh boots. The fixed build
> rejected it with -EINVAL and no KASAN report in 3/3 boots; valid TPM 2.0
> ASN.1 and legacy trusted-key loads continued to succeed.
> 
> The issue was found with an LLM-assisted source audit and validated with an
> end-to-end QEMU and swtpm reproducer.

I did not get any response from you so I'll put one more nit here.

I think it would be better swap these two paragraphs with description
how you address the issue, and why -EINVAL is the right return value
here.

> 
> Fixes: e5fb5d2c5a03 ("security: keys: trusted: Make sealed key properly interoperable")
> Cc: stable@vger.kernel.org
> Signed-off-by: Daehyeon Ko <4ncienth@gmail.com>
> ---
> Changes in v2:
> - Describe the wrapper as the TPM 2.0 ASN.1 key format.
> - Explain the eight-byte minimum next to the check.
> - Return -EINVAL for a malformed TPMT_PUBLIC instead of -E2BIG.
> - Replace the obsolete Assisted-by trailer with changelog disclosure.
> 
> v1: https://lore.kernel.org/r/20260925095308.3248297-1-4ncienth@gmail.com
> 
>  security/keys/trusted-keys/trusted_tpm2.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/security/keys/trusted-keys/trusted_tpm2.c b/security/keys/trusted-keys/trusted_tpm2.c
> index 30188a0ec6766..fb45795b53327 100644
> --- a/security/keys/trusted-keys/trusted_tpm2.c
> +++ b/security/keys/trusted-keys/trusted_tpm2.c
> @@ -425,6 +425,13 @@ static int tpm2_load_cmd(struct tpm_chip *chip,
>  	if (private_len + 2 + public_len + 2 > blob_len)
>  		return -E2BIG;
>  
> +	/*
> +	 * TPMT_PUBLIC starts with type (2), nameAlg (2), and
> +	 * objectAttributes (4), which is read below.
> +	 */
> +	if (public_len < 8)
> +		return -EINVAL;
> +

I don't think that this nails it as well what this protects against as
what I proposed and it does not wrap at 80 chacters.

However, I think what is better here are the sizes in parentheses so
take my comment and add sizes to it (and wrap to 80 characters).

>  	pub = blob + 2 + private_len + 2;
>  	/* key attributes are always at offset 4 */
>  	attrs = get_unaligned_be32(pub + 4);
> 
> base-commit: 722658cac48a6ba49f5506fd74d010ad9dbb2f05
> -- 
> 2.55.0
> 

Br, Jarkko