[Toybox] [PATCH] getfattr.c: fix overlayfs merged dir stuck

[Rob Landley]

On 8/31/22 05:35, Rob Landley wrote:
> On 8/30/22 10:31, Weizhao Ouyang wrote:
>> When getfattx reading overlayfs merged dirs, listxattr will got
>> different keys_len with zero size and determined size, then it will
>> stuck in this while scope. Update the keys_len after the second
>> listxattr to fix it.
> 
> Do you have a test case I can use to reproduce this? (I've never used xattrs
> together with overlayfs before.)
> 
> Also, I believe Elliott has a different implementation of getfattr in android
> (for some sort of C++ library reasons, I'd have to check my notes), so he'll
> probably want the test case there too?

Would this approach work for you?

diff --git a/toys/pending/getfattr.c b/toys/pending/getfattr.c
index bf2c04c8..dbbcfde7 100644
--- a/toys/pending/getfattr.c
+++ b/toys/pending/getfattr.c
@@ -33,8 +33,8 @@ static void do_getfattr(char *file)
   ssize_t (*getter)(const char *, const char *, void *, size_t) = getxattr;
   ssize_t (*lister)(const char *, char *, size_t) = listxattr;
   char **sorted_keys;
-  ssize_t keys_len;
-  char *keys, *key;
+  ssize_t keys_len = 0, len2;
+  char *keys = 0, *key;
   int i, key_count;

   if (FLAG(h)) {
@@ -43,14 +43,11 @@ static void do_getfattr(char *file)
   }

   // Collect the keys.
-  while ((keys_len = lister(file, NULL, 0))) {
-    if (keys_len == -1) perror_msg("listxattr failed");
-    keys = xmalloc(keys_len);
-    if (lister(file, keys, keys_len) == keys_len) break;
-    free(keys);
+  while (keys_len != (len2 = lister(file, keys, keys_len))) {
+    if (keys_len == -1) perror_exit("listxattr");
+    keys = xrealloc(keys, keys_len = len2);
   }
-
-  if (keys_len == 0) return;
+  if (!keys_len) return;

   // Sort the keys.
   for (key = keys, key_count = 0; key-keys < keys_len; key += strlen(key)+1)