W1: w1_therm fix user buffer overflow and cat

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>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 20 insertions, 35 deletions

diff --git a/drivers/w1/slaves/w1_therm.c b/drivers/w1/slaves/w1_therm.c
index e87f464a6fb0..7de99dfd11c8 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)