From: Jiangshan Yi <[email protected]> [ Upstream commit 9b522400bf5c082feb9a0037a053ea822a2c7e4d ]
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: [email protected] # v6.12+ Fixes: 1b6d7f9eb150 ("tpm: add session encryption protection to tpm2_get_random()") Reported-by: Sashiko <[email protected]> Closes: https://sashiko.dev/#/patchset/20260902074839.417419-1-yijiangshan%40kylinos.cn Signed-off-by: Jiangshan Yi <[email protected]> Reviewed-by: Jarkko Sakkinen <[email protected]> Link: https://lore.kernel.org/r/[email protected] Signed-off-by: Jarkko Sakkinen <[email protected]> --- 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 52ee350da867..e12e245faeb1 100644 --- a/drivers/char/tpm/tpm2-cmd.c +++ b/drivers/char/tpm/tpm2-cmd.c @@ -318,7 +318,7 @@ 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) { err = -EFAULT; -- 2.47.3
