[PATCH 3/5] hwmon: (pmbus/adm1266) reject implausible blackbox record_count

[Abdurrahman Hussain]

adm1266_nvmem_read_blackbox() loops over a record_count that comes
straight from byte 3 of the BLACKBOX_INFO response.  The destination
buffer is data->dev_mem, sized for the nvmem cell's declared 2048
bytes (ADM1266_BLACKBOX_MAX_RECORDS * ADM1266_BLACKBOX_SIZE = 32 * 64).
A device that reports a record_count greater than 32 -- whether due
to firmware bugs, bus corruption, or a non-responsive slave returning
0xff -- would walk read_buff past the end of the dev_mem allocation
on the trailing iterations.

Cap record_count at ADM1266_BLACKBOX_MAX_RECORDS (introduced here)
before entering the loop and return -EIO on any larger value, so a
malformed BLACKBOX_INFO response cannot drive the loop out of bounds.

Fixes: 15609d189302 ("hwmon: (pmbus/adm1266) read blackbox")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Abdurrahman Hussain <abdurrahman@xxxxxxxxxx>
---
 drivers/hwmon/pmbus/adm1266.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/hwmon/pmbus/adm1266.c b/drivers/hwmon/pmbus/adm1266.c
index 94691dec1359..43d9e7407795 100644
--- a/drivers/hwmon/pmbus/adm1266.c
+++ b/drivers/hwmon/pmbus/adm1266.c
@@ -46,6 +46,7 @@
 
 #define ADM1266_BLACKBOX_OFFSET		0
 #define ADM1266_BLACKBOX_SIZE		64
+#define ADM1266_BLACKBOX_MAX_RECORDS	32
 
 #define ADM1266_PMBUS_BLOCK_MAX		255
 
@@ -360,6 +361,8 @@ static int adm1266_nvmem_read_blackbox(struct adm1266_data *data, u8 *read_buff)
 		return -EIO;
 
 	record_count = buf[3];
+	if (record_count > ADM1266_BLACKBOX_MAX_RECORDS)
+		return -EIO;
 
 	for (index = 0; index < record_count; index++) {
 		ret = adm1266_pmbus_block_xfer(data, ADM1266_READ_BLACKBOX, 1, &index, read_buff);

-- 
2.53.0