[PATCH v5] tpm: infineon: add bounds check in tpm_inf_recv

[Shahriyar Jalayeri <shahriyar@posteo.de>]

Add two buffer size validations to prevent buffer overflows in
tpm_inf_recv():

1. Validate that the provided buffer can hold at least the 4-byte header
   before attempting to read it.
2. Validate that the buffer is large enough to hold the data size reported
   by the TPM before reading the payload.

Without these checks, a malicious or malfunctioning TPM could cause buffer
overflows by reporting data sizes larger than the provided buffer, leading
to memory corruption.

Fixes: ebb81fdb3dd0 ("[PATCH] tpm: Support for Infineon TPM")
Signed-off-by: Shahriyar Jalayeri <shahriyar@posteo.de>
---
Changelog:
v5:
	- replaced space indentation with tabs before the header comment
v4:
	- removed the curly braces around one line statements
v3:
	- removed dev_err() logs
	- added missing "fixes" tag
	- described header structure
	- fixed commit message length
	- removed use of local variable as constant
	- fixed check to account for off-by-six bytes
v2: 
	- added complete changes in the commit message
	- dev_err() logged expected sizes and stated operation is aborted

 drivers/char/tpm/tpm_infineon.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/char/tpm/tpm_infineon.c b/drivers/char/tpm/tpm_infineon.c
index 7638b65b8..d76aae08b 100644
--- a/drivers/char/tpm/tpm_infineon.c
+++ b/drivers/char/tpm/tpm_infineon.c
@@ -250,6 +250,10 @@ static int tpm_inf_recv(struct tpm_chip *chip, u8 * buf, size_t count)
 	number_of_wtx = 0;
 
 recv_begin:
+	/* expect at least 1-byte VL header, 1-byte ctrl-tag, 2-byte data size */
+	if (count < 4)
+		return -EIO;
+
 	/* start receiving header */
 	for (i = 0; i < 4; i++) {
 		ret = wait(chip, STAT_RDA);
@@ -268,6 +272,9 @@ static int tpm_inf_recv(struct tpm_chip *chip, u8 * buf, size_t count)
 		/* size of the data received */
 		size = ((buf[2] << 8) | buf[3]);
 
+		if (size + 6 > count)
+			return -EIO;
+
 		for (i = 0; i < size; i++) {
 			wait(chip, STAT_RDA);
 			buf[i] = tpm_data_in(RDFIFO);
-- 
2.43.0