[PATCH 12/30] W1: w1_therm fix user buffer overflow and cat

Evgeniy Polyakov
2008-07-11T13:50:12Z

Fixed data reading bug by replacing binary attribute with device one.

Switching the sysfs read from bin_attribute to device_attribute. The
data is far under PAGE_SIZE so the binary interface isn't required.
As the device_attribute interface will make one call to w1_therm_read per
file open and buffer, the result is, the following problems go away.

buffer overflow:
Execute a short read on w1_slave and w1_therm_read_bin would still
return the full string size worth of data clobbering the user space
buffer when it returned. Switching to device_attribute avoids the
buffer overflow problems. With the snprintf formatted output dealing
with short reads without doing a conversion per read would have
been difficult.
bad behavior:
`cat w1_slave` would cause two temperature conversions to take place.
Previously the code assumed W1_SLAVE_DATA_SIZE would be returned with
each read. It would not return 0 unless the offset was less
than W1_SLAVE_DATA_SIZE. The result was the first read did a
temperature conversion, filled the buffer and returned, the
offset in the second read would be less than
W1_SLAVE_DATA_SIZE and also fill the buffer and return, the
third read would finnally have a big enough offset to return 0
and cause cat to stop. Now w1_therm_read will be called at
most once per open.

Signed-off-by: David Fries <david@fries.net>
Signed-off-by: Evgeniy Polyakov <johnpol@2ka.mipt.ru>

---
drivers/w1/slaves/w1_therm.c | 55 +++++++++++++++--------------------------
drivers/w1/w1.h | 1 -
2 files changed, 20 insertions(+), 36 deletions(-)

diff --git a/drivers/w1/slaves/w1_therm.c b/drivers/w1/slaves/w1_therm.c
index e87f464..7de99df 100644
--- a/drivers/w1/slaves/w1_therm.c
+++ b/drivers/w1/slaves/w1_therm.c
@@ -50,26 +50,20 @@ static u8 bad_roms[][9] = {
{}
};

-static ssize_t w1_therm_read_bin(struct kobject *, struct bin_attribute *,
- char *, loff_t, size_t);
+static ssize_t w1_therm_read(struct device *device,
+ struct device_attribute *attr, char *buf);

-static struct bin_attribute w1_therm_bin_attr = {
- .attr = {
- .name = "w1_slave",
- .mode = S_IRUGO,
- },
- .size = W1_SLAVE_DATA_SIZE,
- .read = w1_therm_read_bin,
-};
+static struct device_attribute w1_therm_attr =
+ __ATTR(w1_slave, S_IRUGO, w1_therm_read, NULL);

static int w1_therm_add_slave(struct w1_slave *sl)
{
- return sysfs_create_bin_file(&sl->dev.kobj, &w1_therm_bin_attr);
+ return device_create_file(&sl->dev, &w1_therm_attr);
}

static void w1_therm_remove_slave(struct w1_slave *sl)
{
- sysfs_remove_bin_file(&sl->dev.kobj, &w1_therm_bin_attr);
+ device_remove_file(&sl->dev, &w1_therm_attr);
}

static struct w1_family_ops w1_therm_fops = {
@@ -168,30 +162,19 @@ static int w1_therm_check_rom(u8 rom[9])
return 0;
}

-static ssize_t w1_therm_read_bin(struct kobject *kobj,
- struct bin_attribute *bin_attr,
- char *buf, loff_t off, size_t count)
+static ssize_t w1_therm_read(struct device *device,
+ struct device_attribute *attr, char *buf)
{
- struct w1_slave *sl = kobj_to_w1_slave(kobj);
+ struct w1_slave *sl = dev_to_w1_slave(device);
struct w1_master *dev = sl->master;
u8 rom[9], crc, verdict;
int i, max_trying = 10;
+ ssize_t c = PAGE_SIZE;

mutex_lock(&sl->master->mutex);

- if (off > W1_SLAVE_DATA_SIZE) {
- count = 0;
- goto out;
- }
- if (off + count > W1_SLAVE_DATA_SIZE) {
- count = 0;
- goto out;
- }
-
- memset(buf, 0, count);
memset(rom, 0, sizeof(rom));

- count = 0;
verdict = 0;
crc = 0;

@@ -211,7 +194,9 @@ static ssize_t w1_therm_read_bin(struct kobject *kobj,

w1_write_8(dev, W1_READ_SCRATCHPAD);
if ((count = w1_read_block(dev, rom, 9)) != 9) {
- dev_warn(&dev->dev, "w1_read_block() returned %d instead of 9.\n", count);
+ dev_warn(device, "w1_read_block() "
+ "returned %u instead of 9.\n",
+ count);
}

crc = w1_calc_crc8(rom, 8);
@@ -226,22 +211,22 @@ static ssize_t w1_therm_read_bin(struct kobject *kobj,
}

for (i = 0; i < 9; ++i)
- count += sprintf(buf + count, "%02x ", rom[i]);
- count += sprintf(buf + count, ": crc=%02x %s\n",
+ c -= snprintf(buf + PAGE_SIZE - c, c, "%02x ", rom[i]);
+ c -= snprintf(buf + PAGE_SIZE - c, c, ": crc=%02x %s\n",
crc, (verdict) ? "YES" : "NO");
if (verdict)
memcpy(sl->rom, rom, sizeof(sl->rom));
else
- dev_warn(&dev->dev, "18S20 doesn't respond to CONVERT_TEMP.\n");
+ dev_warn(device, "18S20 doesn't respond to CONVERT_TEMP.\n");

for (i = 0; i < 9; ++i)
- count += sprintf(buf + count, "%02x ", sl->rom[i]);
+ c -= snprintf(buf + PAGE_SIZE - c, c, "%02x ", sl->rom[i]);

- count += sprintf(buf + count, "t=%d\n", w1_convert_temp(rom, sl->family->fid));
-out:
+ c -= snprintf(buf + PAGE_SIZE - c, c, "t=%d\n",
+ w1_convert_temp(rom, sl->family->fid));
mutex_unlock(&dev->mutex);

- return count;
+ return PAGE_SIZE - c;
}

static int __init w1_therm_init(void)
diff --git a/drivers/w1/w1.h b/drivers/w1/w1.h
index 00b84ab..cdaa6ff 100644
--- a/drivers/w1/w1.h
+++ b/drivers/w1/w1.h
@@ -46,7 +46,6 @@ struct w1_reg_num
#include "w1_family.h"

#define W1_MAXNAMELEN 32
-#define W1_SLAVE_DATA_SIZE 128

#define W1_SEARCH 0xF0
#define W1_ALARM_SEARCH 0xEC
--
1.4.4.4