[PATCH 6.6 324/567] hwmon: (pmbus/q54sj108a2) fix stack overflow in debugfs read

Greg Kroah-Hartman
2026-03-23T15:08:32Z

6.6-stable review patch. If anyone has any objections, please let me know.

------------------

From: Sanman Pradhan <psanman@juniper.net>

commit 25dd70a03b1f5f3aa71e1a5091ecd9cd2a13ee43 upstream.

The q54sj108a2_debugfs_read function suffers from a stack buffer overflow
due to incorrect arguments passed to bin2hex(). The function currently
passes 'data' as the destination and 'data_char' as the source.

Because bin2hex() converts each input byte into two hex characters, a
32-byte block read results in 64 bytes of output. Since 'data' is only
34 bytes (I2C_SMBUS_BLOCK_MAX + 2), this writes 30 bytes past the end
of the buffer onto the stack.

Additionally, the arguments were swapped: it was reading from the
zero-initialized 'data_char' and writing to 'data', resulting in
all-zero output regardless of the actual I2C read.

Fix this by:
1. Expanding 'data_char' to 66 bytes to safely hold the hex output.
2. Correcting the bin2hex() argument order and using the actual read count.
3. Using a pointer to select the correct output buffer for the final
simple_read_from_buffer call.

Fixes: d014538aa385 ("hwmon: (pmbus) Driver for Delta power supplies Q54SJ108A2")
Cc: stable@vger.kernel.org
Signed-off-by: Sanman Pradhan <psanman@juniper.net>
Link: https://lore.kernel.org/r/20260304235116.1045-1-sanman.p211993@gmail.com
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/hwmon/pmbus/q54sj108a2.c | 19 ++++++++++---------
1 file changed, 10 insertions(+), 9 deletions(-)

--- a/drivers/hwmon/pmbus/q54sj108a2.c
+++ b/drivers/hwmon/pmbus/q54sj108a2.c
@@ -78,7 +78,8 @@ static ssize_t q54sj108a2_debugfs_read(s
int idx = *idxp;
struct q54sj108a2_data *psu = to_psu(idxp, idx);
char data[I2C_SMBUS_BLOCK_MAX + 2] = { 0 };
- char data_char[I2C_SMBUS_BLOCK_MAX + 2] = { 0 };
+ char data_char[I2C_SMBUS_BLOCK_MAX * 2 + 2] = { 0 };
+ char *out = data;
char *res;

switch (idx) {
@@ -149,27 +150,27 @@ static ssize_t q54sj108a2_debugfs_read(s
if (rc < 0)
return rc;

- res = bin2hex(data, data_char, 32);
- rc = res - data;
-
+ res = bin2hex(data_char, data, rc);
+ rc = res - data_char;
+ out = data_char;
break;
case Q54SJ108A2_DEBUGFS_FLASH_KEY:
rc = i2c_smbus_read_block_data(psu->client, PMBUS_FLASH_KEY_WRITE, data);
if (rc < 0)
return rc;

- res = bin2hex(data, data_char, 4);
- rc = res - data;
-
+ res = bin2hex(data_char, data, rc);
+ rc = res - data_char;
+ out = data_char;
break;
default:
return -EINVAL;
}

- data[rc] = '\n';
+ out[rc] = '\n';
rc += 2;

- return simple_read_from_buffer(buf, count, ppos, data, rc);
+ return simple_read_from_buffer(buf, count, ppos, out, rc);
}

static ssize_t q54sj108a2_debugfs_write(struct file *file, const char __user *buf,