files: Fix test and set endianess problem

Andrew Vagin reported the problem found by a checker:

    CID 174702 (#1 of 1): Out-of-bounds access (INCOMPATIBLE_CAST)
    incompatible_cast: Pointer &f->raw.counter points to an object whose
    effective type is int (32 bits, signed) but is dereferenced as a wider
    unsigned long (64 bits, unsigned). This may lead to memory corruption.

It looks like, this points to real problem, which may happen on big-endian
platforms. In the code I relay on the fact, that FDS_EVENT_BIT has a small
number and the value, it determines, fits into int type without problems.
But it's correct only for little-endian.

In case of big-endian, if the word size is 8 bytes, then FDS_EVENT value
is in the last bytes, so there is an access to wrong memory.

To fix the problem, I suggest to use little-endian byte order to work
with task_st futex. Then, the bits from 0 to 31 will be in the low adresses,
i.e. in task_st futex. There is new primitives test_and_set_bit_le() and
set_bit_le() borrowed from the linux kernel for that.

This fixes the problem, but I suppose, the checker does not see the problem
so deep, and just compares the types size, so it will fail again.
So, let's enlarge the bit field size to silence it.
Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>

criu/files.c

@@ -156,30 +156,33 @@ out:
 int set_fds_event(pid_t virt)
 {
 	struct pstree_item *item;
-	int old;
+	bool is_set;
 
 	item = pstree_item_by_virt(virt);
 	BUG_ON(!item);
 
-	old = test_and_set_bit(FDS_EVENT_BIT, (unsigned long *)&item->task_st);
+	is_set = !!test_and_set_bit_le(FDS_EVENT_BIT, &item->task_st_le_bits);
 
-	if (!(old & FDS_EVENT))
+	if (!is_set)
 		futex_wake(&item->task_st);
 	return 0;
 }
 
 void clear_fds_event(void)
 {
-	futex_t *f = &current->task_st;
-
-	clear_bit(FDS_EVENT_BIT, (unsigned long *)&f->raw.counter);
+	clear_bit_le(FDS_EVENT_BIT, &current->task_st_le_bits);
 }
 
 void wait_fds_event(void)
 {
 	futex_t *f = &current->task_st;
-
-	futex_wait_if_cond(f, FDS_EVENT, &);
+	int value;
+#if BITS_PER_LONG == 64
+	value = htole64(FDS_EVENT);
+#else
+	value = htole32(FDS_EVENT);
+#endif
+	futex_wait_if_cond(f, value, &);
 	clear_fds_event();
 }
 

criu/include/pstree.h

@@ -25,7 +25,10 @@ struct pstree_item {
 	struct pid		*threads;	/* array of threads */
 	CoreEntry		**core;
 	TaskKobjIdsEntry	*ids;
-	futex_t			task_st;
+	union {
+		futex_t		task_st;
+		unsigned long	task_st_le_bits;
+	};
 };
 
 enum {

include/common/bitops.h

 #ifndef __CR_COMMON_BITOPS_H__
 #define __CR_COMMON_BITOPS_H__
 #include "common/asm/bitops.h"
+
+#include "common/bitsperlong.h"
+#include <endian.h>
+
+#if __BYTE_ORDER == __BIG_ENDIAN
+#define BITOP_LE_SWIZZLE	((BITS_PER_LONG-1) & ~0x7)
+#else
+#define BITOP_LE_SWIZZLE	0
+#endif
+
+static inline int test_and_set_bit_le(int nr, void *addr)
+{
+	return test_and_set_bit(nr ^ BITOP_LE_SWIZZLE, addr);
+}
+
+static inline void clear_bit_le(int nr, void *addr)
+{
+	clear_bit(nr ^ BITOP_LE_SWIZZLE, addr);
+}
 #endif