From 9b522400bf5c082feb9a0037a053ea822a2c7e4d Mon Sep 17 00:00:00 2001 From: Jiangshan Yi Date: Thu, 3 Sep 2026 11:58:37 +0800 Subject: [PATCH] tpm: fix off-by-four bounds check in tpm2_get_random() When the response carries the TPM2_ST_SESSIONS tag, tpm2_get_random() skips the 4-byte parameter size field before locating the random data, but the bounds check still validates the response length against TPM_HEADER_SIZE. A truncated response can pass the check and make memcpy() read up to 4 bytes past the response end, so stale buffer contents end up in the caller's random bytes. Fix this by checking the response length against 'offset', which already includes the skipped parameter size field. Cc: stable@vger.kernel.org # v6.12+ Fixes: 1b6d7f9eb150 ("tpm: add session encryption protection to tpm2_get_random()") Reported-by: Sashiko Closes: https://sashiko.dev/#/patchset/20260902074839.417419-1-yijiangshan%40kylinos.cn Signed-off-by: Jiangshan Yi Reviewed-by: Jarkko Sakkinen Link: https://lore.kernel.org/r/20260903035837.219284-1-yijiangshan@kylinos.cn Signed-off-by: Jarkko Sakkinen --- drivers/char/tpm/tpm2-cmd.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/char/tpm/tpm2-cmd.c b/drivers/char/tpm/tpm2-cmd.c index 96e0e06bbbf0..ae22295df798 100644 --- a/drivers/char/tpm/tpm2-cmd.c +++ b/drivers/char/tpm/tpm2-cmd.c @@ -307,7 +307,7 @@ int tpm2_get_random(struct tpm_chip *chip, u8 *dest, size_t max) out = (struct tpm2_get_random_out *)&buf->data[offset]; recd = min_t(u32, be16_to_cpu(out->size), num_bytes); if (tpm_buf_length(buf) < - TPM_HEADER_SIZE + + offset + offsetof(struct tpm2_get_random_out, buffer) + recd) { tpm2_end_auth_session(chip);