[{"id":3684747,"web_url":"http://patchwork.ozlabs.org/comment/3684747/","msgid":"<92d20108-aa75-40ee-a561-3fbab0fbebad@linux.ibm.com>","list_archive_url":null,"date":"2026-04-30T14:32:17","subject":"Re: [PATCH v2 2/2] tpm_emulator: Limit number of bytes read to\n negotiated buffer size","submitter":{"id":75097,"url":"http://patchwork.ozlabs.org/api/people/75097/","name":"Stefan Berger","email":"stefanb@linux.ibm.com"},"content":"On 4/30/26 10:23 AM, Stefan Berger wrote:\n> Limit the number of bytes read from the TPM response to the size of the\n> receiving buffer, which is the same as the size of the buffer negotiated\n> with swtpm.\n> \n> The TPM TIS and SPAPR use 4096 bytes and the CRB 3968 bytes. There are\n> currently no TPM 2 responses using this size of a buffer and therefore\n> no response will be sent that is exceeding this size.\n> \n> Signed-off-by: Stefan Berger \n> ---\n> backends/tpm/tpm_emulator.c | 11 ++++++++---\n> 1 file changed, 8 insertions(+), 3 deletions(-)\n> \n> diff --git a/backends/tpm/tpm_emulator.c b/backends/tpm/tpm_emulator.c\n> index 10ab909474..b8ae113774 100644\n> --- a/backends/tpm/tpm_emulator.c\n> +++ b/backends/tpm/tpm_emulator.c\n> @@ -176,8 +176,9 @@ static int tpm_emulator_unix_tx_bufs(TPMEmulator *tpm_emu,\n> bool *selftest_done,\n> Error **errp)\n> {\n> - ssize_t ret;\n> bool is_selftest = false;\n> + size_t to_read;\n> + ssize_t ret;\n> \n> if (selftest_done) {\n> *selftest_done = false;\n> @@ -195,9 +196,13 @@ static int tpm_emulator_unix_tx_bufs(TPMEmulator *tpm_emu,\n> return -1;\n> }\n> \n> + /*\n> + * Size of response from swtpm must be <= out_len (= negotiated buffer size)\n> + */\n> + to_read = MIN(tpm_cmd_get_size(out) - sizeof(struct tpm_resp_hdr), out_len);\n\nIt should be:\n\nto_read = MIN(tpm_cmd_get_size(out), out_len) - sizeof(struct tpm_resp_hdr);\n\n> +\n> ret = qio_channel_read_all(tpm_emu->data_ioc,\n> - (char *)out + sizeof(struct tpm_resp_hdr),\n> - tpm_cmd_get_size(out) - sizeof(struct tpm_resp_hdr), errp);\n> + (char *)out + sizeof(struct tpm_resp_hdr), to_read, errp);\n> if (ret != 0) {\n> return -1;\n> }","headers":{"Return-Path":"","X-Original-To":"incoming@patchwork.ozlabs.org","Delivered-To":"patchwork-incoming@legolas.ozlabs.org","Authentication-Results":["legolas.ozlabs.org;\n\tdkim=pass (2048-bit key;\n unprotected) header.d=ibm.com header.i=@ibm.com header.a=rsa-sha256\n header.s=pp1 header.b=ntGLGdlo;\n\tdkim-atps=neutral","legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=nongnu.org\n (client-ip=209.51.188.17; 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