hwmon: (pmbus/q54sj108a2) fix stack overflow in debugfs read

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>

diff --git a/drivers/hwmon/pmbus/q54sj108a2.c b/drivers/hwmon/pmbus/q54sj108a2.c
index fc030ca34480c64557af699a6061994c044250f7..d5d60a9af8c589f47193e8a182d25a0ba593a8b3 100644 (file)
--- a/drivers/hwmon/pmbus/q54sj108a2.c
+++ b/drivers/hwmon/pmbus/q54sj108a2.c
@@ -79,7 +79,8 @@ static ssize_t q54sj108a2_debugfs_read(struct file *file, char __user *buf,
        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) {
@@ -150,27 +151,27 @@ static ssize_t q54sj108a2_debugfs_read(struct file *file, char __user *buf,
                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,