char: tpm: tpm-buf: Add sanity check fallback in read helpers

JIRA: https://issues.redhat.com/browse/RHEL-72765

Upstream Status: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git

commit 32d495b
Author: Purva Yeshi <purvayeshi550@gmail.com>
Date:   Thu Apr 10 16:04:42 2025 +0530

    char: tpm: tpm-buf: Add sanity check fallback in read helpers

    Fix Smatch-detected issue:

    drivers/char/tpm/tpm-buf.c:208 tpm_buf_read_u8() error:
    uninitialized symbol 'value'.
    drivers/char/tpm/tpm-buf.c:225 tpm_buf_read_u16() error:
    uninitialized symbol 'value'.
    drivers/char/tpm/tpm-buf.c:242 tpm_buf_read_u32() error:
    uninitialized symbol 'value'.

    Zero-initialize the return values in tpm_buf_read_u8(), tpm_buf_read_u16(),
    and tpm_buf_read_u32() to guard against uninitialized data in case of a
    boundary overflow.

    Add defensive initialization ensures the return values are always defined,
    preventing undefined behavior if the unexpected happens.

    Signed-off-by: Purva Yeshi <purvayeshi550@gmail.com>
    Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
    Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
    Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>

Signed-off-by: Štěpán Horáček <shoracek@redhat.com>

Author: shoracek

drivers/char/tpm/tpm-buf.c

@@ -180,7 +180,7 @@ static void tpm_buf_read(struct tpm_buf *buf, off_t *offset, size_t count, void
  */
 u8 tpm_buf_read_u8(struct tpm_buf *buf, off_t *offset)
 {
-	u8 value;
+	u8 value = 0;
 
 	tpm_buf_read(buf, offset, sizeof(value), &value);
 
@@ -197,7 +197,7 @@ EXPORT_SYMBOL_GPL(tpm_buf_read_u8);
  */
 u16 tpm_buf_read_u16(struct tpm_buf *buf, off_t *offset)
 {
-	u16 value;
+	u16 value = 0;
 
 	tpm_buf_read(buf, offset, sizeof(value), &value);
 
@@ -214,7 +214,7 @@ EXPORT_SYMBOL_GPL(tpm_buf_read_u16);
  */
 u32 tpm_buf_read_u32(struct tpm_buf *buf, off_t *offset)
 {
-	u32 value;
+	u32 value = 0;
 
 	tpm_buf_read(buf, offset, sizeof(value), &value);