drivers: w1: make w1_slave::flags long to avoid memory corruption

On architectures where long is more then 32 bits, modifying a 32-bit field
with set_bit (and other atomic bit operations) may cause bytes following
the field to by modified.

Because the endianness of the bits within a field is the native endianness
of the CPU[1], on big-endian machines, bit number zero is in the last byte
of the field.

Therefore, `set_bit(0, ptr)' on a 64-bit big-endian machine is roughly
equivalent to `((char *)ptr)[7] |= 1', and since w1 driver uses a 32-bit
field for holding the flags, this causes bytes beyond the field to be
modified.

[1] From Documentation/atomic_ops.txt:

    Native atomic bit operations are defined to operate on objects
    aligned to the size of an "unsigned long" C data type, and are
    least of that size.  The endianness of the bits within each
    "unsigned long" are the native endianness of the cpu.

Signed-off-by: Michal Nazarewicz <mina86@mina86.com>
Cc: Evgeniy Polyakov <zbr@ioremap.net>
Cc: Greg KH <greg@kroah.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 1 insertions, 1 deletions

diff --git a/drivers/w1/w1.h b/drivers/w1/w1.h
index 45908e56c2f8..ca8081a101d6 100644
--- a/drivers/w1/w1.h
+++ b/drivers/w1/w1.h
@@ -67,8 +67,8 @@ struct w1_slave
 	struct w1_reg_num	reg_num;
 	atomic_t		refcnt;
 	u8			rom[9];
-	u32			flags;
 	int			ttl;
+	unsigned long		flags;
 
 	struct w1_master	*master;
 	struct w1_family	*family;