9p: local: always return -1 on error in local_unlinkat_common

local_unlinkat_common() is supposed to always return -1 on error.
This is being done by jumps to the 'err_out' label, which is
a 'return ret' call, and 'ret' is initialized with -1.

Unfortunately there is a condition in which the function will
return 0 on error: in a case where flags == AT_REMOVEDIR, 'ret'
will be 0 when reaching

map_dirfd = openat_dir(...)

And, if map_dirfd == -1 and errno != ENOENT, the existing 'err_out'
jump will execute 'return ret', when ret is still set to zero
at that point.

This patch fixes it by changing all 'err_out' labels by
'return -1' calls, ensuring that the function will always
return -1 on error conditions. 'ret' can be left unintialized
since it's now being used just to store the result of 'unlinkat'
calls.

CC: Greg Kurz <groug@kaod.org>
Signed-off-by: NDaniel Henrique Barboza <danielhb413@gmail.com>
[groug: changed prefix in title to be "9p: local:"]
Signed-off-by: NGreg Kurz <groug@kaod.org>

hw/9pfs/9p-local.c

@@ -1076,7 +1076,7 @@ out:
 static int local_unlinkat_common(FsContext *ctx, int dirfd, const char *name,
                                  int flags)
 {
-    int ret = -1;
+    int ret;
 
     if (ctx->export_flags & V9FS_SM_MAPPED_FILE) {
         int map_dirfd;
@@ -1094,12 +1094,12 @@ static int local_unlinkat_common(FsContext *ctx, int dirfd, const char *name,
 
             fd = openat_dir(dirfd, name);
             if (fd == -1) {
-                goto err_out;
+                return -1;
             }
             ret = unlinkat(fd, VIRTFS_META_DIR, AT_REMOVEDIR);
             close_preserve_errno(fd);
             if (ret < 0 && errno != ENOENT) {
-                goto err_out;
+                return -1;
             }
         }
         map_dirfd = openat_dir(dirfd, VIRTFS_META_DIR);
@@ -1107,16 +1107,14 @@ static int local_unlinkat_common(FsContext *ctx, int dirfd, const char *name,
             ret = unlinkat(map_dirfd, name, 0);
             close_preserve_errno(map_dirfd);
             if (ret < 0 && errno != ENOENT) {
-                goto err_out;
+                return -1;
             }
         } else if (errno != ENOENT) {
-            goto err_out;
+            return -1;
         }
     }
 
-    ret = unlinkat(dirfd, name, flags);
-err_out:
-    return ret;
+    return unlinkat(dirfd, name, flags);
 }
 
 static int local_remove(FsContext *ctx, const char *path)