/proc/sysvipc/shm: fix 32-bit truncation of segment sizes

sysvipc_shm_proc_show() picks between format strings (based on the
expected maximum length of a SHM segment) in a way that prevents gcc from
performing format checks on the seq_printf() parameters. This hid two
format errors - shp->shm_segsz and shp->shm_nattach are both unsigned
long, but were being printed as unsigned int and signed int respectively.
This leads to 32-bit truncation of SHM segment sizes reported in
/proc/sysvipc/shm. (And for nattach, but that's less of a problem for
most users).

This patch makes the format string directly visible to gcc's format
specifier checker, and fixes the two broken format specifiers.

Signed-off-by: Paul Menage <[e-mail]>
Cc: Nadia Derbey <[e-mail]>
Cc: Manfred Spraul <[e-mail]>
Cc: Pierre Peiffer <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

ipc/shm.c

···
 static int sysvipc_shm_proc_show(struct seq_file *s, void *it)
 {
 	struct shmid_kernel *shp = it;
-	char *format;
 
-#define SMALL_STRING "%10d %10d  %4o %10u %5u %5u  %5d %5u %5u %5u %5u %10lu %10lu %10lu\n"
-#define BIG_STRING   "%10d %10d  %4o %21u %5u %5u  %5d %5u %5u %5u %5u %10lu %10lu %10lu\n"
+#if BITS_PER_LONG <= 32
+#define SIZE_SPEC "%10lu"
+#else
+#define SIZE_SPEC "%21lu"
+#endif
 
-	if (sizeof(size_t) <= sizeof(int))
-		format = SMALL_STRING;
-	else
-		format = BIG_STRING;
-	return seq_printf(s, format,
+	return seq_printf(s,
+			  "%10d %10d  %4o " SIZE_SPEC " %5u %5u  "
+			  "%5lu %5u %5u %5u %5u %10lu %10lu %10lu\n",
 			  shp->shm_perm.key,
 			  shp->shm_perm.id,
 			  shp->shm_perm.mode,