On Fri, Sep 25, 2026 at 08:42:09PM +0530, Srish Srinivasan wrote: > Hi Jarkko, > Thanks for taking a look. > > On 9/25/26 4:51 PM, Jarkko Sakkinen wrote: > > On Fri, Sep 18, 2026 at 12:18:25PM +0530, Srish Srinivasan wrote: > > > On 9/18/26 7:40 AM, Jarkko Sakkinen wrote: > > > > On Thu, Sep 10, 2026 at 03:32:22PM +0530, Srish Srinivasan wrote: > > > > > TPM2_Create returns outPrivate, outPublic, creationData, creationHash > > > > > and > > > > > creationTicket in its response parameter area. However, only > > > > > outPrivate and > > > > > outPublic are included in the trusted key blob. The size of the blob > > > > > is > > > > > therefore not determined by the size of the complete response > > > > > parameter > > > > > area. > > > > > > > > > > tpm2_seal_trusted() currently compares the size of the complete > > > > > response > > > > > parameter area against MAX_BLOB_SIZE. This can reject a valid response > > > > > when the remaining response outputs cause the entire response > > > > > parameter > > > > > area to exceed MAX_BLOB_SIZE, even though the outPrivate and outPublic > > > > > TPM2B structures consumed by tpm2_key_encode() remain small enough to > > > > > be > > > > > encoded in the key blob. > > > > > > > > > > This is observed when creating larger trusted keys using an swtpm TPM > > > > > 2.0 > > > > > emulator backed by libtpms. > > > > > > > > > > For example, requesting a 113-byte key succeeds, 114 fails. > > > > > > > > > > ~$ keyctl add trusted trusted_key1 "new 113 keyhandle=0x81000001" @u > > > > > 520504613 > > > > > ~$ keyctl add trusted trusted_key2 "new 114 keyhandle=0x81000001" @u > > > > > add_key: Argument list too long > > > > > ~$ > > > > > > > > > > Remove the MAX_BLOB_SIZE check on the complete response parameter > > > > > area. > > > > > Instead, use the response length passed to tpm2_key_encode() to > > > > > validate > > > > > that the outPrivate and outPublic TPM2B structures are fully contained > > > > > in the response before accessing them. > > > > > > > > > > Previously, a response parameter area larger than MAX_BLOB_SIZE was > > > > > rejected with -E2BIG before ASN.1 encoding. With this change, if the > > > > > resulting encoded blob does not fit in payload->blob, the error > > > > > returned by > > > > > asn1_encode_sequence() is propagated instead. > > > > > > > > > > Signed-off-by: Srish Srinivasan <[email protected]> > > > > > --- > > > > > Changelog: > > > > > > > > > > v2: > > > > > - Exclude a comment pointed out by Jarkko > > > > > > > > > > security/keys/trusted-keys/trusted_tpm2.c | 35 > > > > > +++++++++++++++++------ > > > > > 1 file changed, 27 insertions(+), 8 deletions(-) > > > > > > > > > > diff --git a/security/keys/trusted-keys/trusted_tpm2.c > > > > > b/security/keys/trusted-keys/trusted_tpm2.c > > > > > index 01f18bb37047..cbec4f591952 100644 > > > > > --- a/security/keys/trusted-keys/trusted_tpm2.c > > > > > +++ b/security/keys/trusted-keys/trusted_tpm2.c > > > > > @@ -24,24 +24,42 @@ static int tpm2_key_encode(struct > > > > > trusted_key_payload *payload, > > > > > u8 *src, u32 len) > > > > > { > > > > > const int SCRATCH_SIZE = PAGE_SIZE; > > > > > - u8 *scratch = kmalloc(SCRATCH_SIZE, GFP_KERNEL); > > > > > - u8 *work = scratch, *work1; > > > > > - u8 *end_work = scratch + SCRATCH_SIZE; > > > > > + u8 *scratch; > > > > > + u8 *work, *work1; > > > > > + u8 *end_work; > > > > > u8 *priv, *pub; > > > > > - u16 priv_len, pub_len; > > > > > + u32 priv_len, pub_len; > > > > > int ret; > > > > > - priv_len = get_unaligned_be16(src) + 2; > > > > > + if (len < sizeof(__be16)) > > > > > + return -EFAULT; > > > > > + > > > > > + priv_len = get_unaligned_be16(src); > > > > > + if (priv_len > len - sizeof(__be16)) > > > > > + return -EFAULT; > > > > > + > > > > > + priv_len += sizeof(__be16); > > > > > priv = src; > > > > > + if (len - priv_len < sizeof(__be16)) > > > > > + return -EFAULT; > > > > This caused for me some head scrathing tbh. > > > > > > > > See: > > > > > > > > 1. len >= 2 > > > > 2. priv_len <= len - 2 > > > > 3. 2 - priv_len + priv_len <= 2 - priv_len + len - 2 > > > > 4. 2 <= len - priv_len > > > > > > > > Is this check required? > > > > > > Hi Jarkko, > > > Thanks for taking a look. > > > > > > The preceding check, > > > > > > > > > if (priv_len > len - sizeof(__be16)) > > > return -EFAULT; > > > > > > > > > ensures that the complete TPM2B_PRIVATE, including its size field, > > > fits within len. After this check, priv_len is incremented by 2 and > > > therefore represents the complete TPM2B_PRIVATE length. > > > > > > > > > The check you pointed out, > > > > > > > > > if (len - priv_len < sizeof(__be16)) > > > return -EFAULT; > > > > > > > > > then ensures that at least 2 bytes remain for reading the following > > > TPM2B_PUBLIC size field. > > OK, maybe I got something wrong in my deduction but I'm not > > still entirely sure whether this is leanest way to do these > > checks. > > > Sure, I will simplify this. Would the following be better? > > > if (len < 4) > return -EINVAL; > > priv_len = get_unaligned_be16(src) + 2; > if (priv_len + 2 > len) > return -EIO; > > priv = src; > src += priv_len; > > pub_len = get_unaligned_be16(src) + 2; > if (priv_len + pub_len > len) > return -EIO; > > pub = src; > > > The first check ensures that len can contain both TPM2B size fields. > The second verifies that the complete TPM2B_PRIVATE leaves room for the > TPM2B_PUBLIC size field. The final check ensures that both the complete > TPM2B_PRIVATE and TPM2B_PUBLIC structures fit within len. > > > > > I'll iterate some other remarks so that this can move forward. > > > > I was not either entirely sure why this was done: > > > > - u16 priv_len, pub_len; > > + u32 priv_len, pub_len; > > > Yes, so the change from u16 to u32 was because the values stored in priv_len > and > pub_len include both the 16-bit value read from the response and the > two-byte TPM2B > size field. > > > > > > Why wrong len causes -EFAULT and not -EINVAL? EFAULT is for > > memory failures. Probably two that follow should return -EIO. > > > Agreed, I will fix this. > > > > > > One more that came to mind: > > > > - priv_len = get_unaligned_be16(src) + 2; > > + if (len < sizeof(__be16)) > > + return -EFAULT; > > + > > + priv_len = get_unaligned_be16(src); > > + if (priv_len > len - sizeof(__be16)) > > + return -EFAULT; > > + > > + priv_len += sizeof(__be16); > > > > Removing the line above is not necessary and neither is the last > > the last statement if you just change your check accordingly. > > > Yes, that's right. And I have made this change in the diff > that I have pasted above. > > Please let me know if this looks better now. > > And, thanks for the feedback.
Yeah, so this is a patch that needs a few iterations I'm not against the change itself per se :-) I think it would make sense to declare "u8 *scratch __free(kfree)" while at it so that rollback does not complicate this function further. > > > > > > > BR, Jarkko > > > Thanks, > Srish. > Br, Jarkko
