um: Remove use of asprinf in umid.c

asprintf is not compatible with the existing uml memory allocation
mechanism. Its use on the "user" side of UML results in a corrupt slab
state.

Fixes: 0d4e5ac ("um: remove uses of variable length arrays")
Cc: stable@vger.kernel.org
Signed-off-by: Anton Ivanov <anton.ivanov@cambridgegreys.com>
Signed-off-by: Richard Weinberger <richard@nod.at>

arch/um/os-Linux/umid.c

@@ -137,20 +137,13 @@ static inline int is_umdir_used(char *dir)
 {
  char pid[sizeof("nnnnnnnnn")], *end, *file;
  int dead, fd, p, n, err;
- size_t filelen;
+ size_t filelen = strlen(dir) + sizeof("/pid") + 1;
 
- err = asprintf(&file, "%s/pid", dir);
- if (err < 0)
- return 0;
-
- filelen = strlen(file);
+ file = malloc(filelen);
+ if (!file)
+ return -ENOMEM;
 
- n = snprintf(file, filelen, "%s/pid", dir);
- if (n >= filelen) {
- printk(UM_KERN_ERR "is_umdir_used - pid filename too long\n");
- err = -E2BIG;
- goto out;
- }
+ snprintf(file, filelen, "%s/pid", dir);
 
  dead = 0;
  fd = open(file, O_RDONLY);