[PATCH v2] char: tpm: tpm-buf: Add sanity check fallback in read helpers

[Purva Yeshi <purvayeshi550@gmail.com>]

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>
---
V1 - https://lore.kernel.org/all/20250409205536.210202-1-purvayeshi550@gmail.com/
V2 - Update commit message to clarify patch adds a sanity check

 drivers/char/tpm/tpm-buf.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/char/tpm/tpm-buf.c b/drivers/char/tpm/tpm-buf.c
index e49a19fea3bd..dc882fc9fa9e 100644
--- a/drivers/char/tpm/tpm-buf.c
+++ b/drivers/char/tpm/tpm-buf.c
@@ -201,7 +201,7 @@ 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);
 
@@ -218,7 +218,7 @@ 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);
 
@@ -235,7 +235,7 @@ 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);
 
-- 
2.34.1