From c532bcdae8259b0f71723cda331ded4dbb0fa908 Mon Sep 17 00:00:00 2001
From: Richard Purdie <richard.purdie@linuxfoundation.org>
Date: Wed, 9 Mar 2016 22:49:02 +0000
Subject: [PATCH] qemu: Limit paths searched during user mode emulation

By default qemu builds a complete list of directories within the user
emulation sysroot (-L option). The OE sysroot directory is large and
this is confusing, for example it indexes all pkgdata. In particular this
confuses strace of qemu binaries with tons of irrelevant paths.

This patch stops the code indexing up front and instead only indexes
things if/as/when it needs to. This drastically reduces the files it
reads and reduces memory usage and cleans up strace.

It would also avoid the infinite directory traversal bug in [YOCTO #6996]
although the code could still be vulnerable if it parsed those specific
paths.

RP
2016/3/9
Upstream-Status: Pending
---
 util/path.c | 44 ++++++++++++++++++++++----------------------
 1 file changed, 22 insertions(+), 22 deletions(-)

diff --git a/util/path.c b/util/path.c
index 7f9fc272fb..a416cd4ac2 100644
--- a/util/path.c
+++ b/util/path.c
@@ -15,6 +15,7 @@ struct pathelem
     char *name;
     /* Full path name, eg. /usr/gnemul/x86-linux/lib. */
     char *pathname;
+    int populated_entries;
     struct pathelem *parent;
     /* Children */
     unsigned int num_entries;
@@ -45,6 +46,7 @@ static struct pathelem *new_entry(const char *root,
     new->name = g_strdup(name);
     new->pathname = g_strdup_printf("%s/%s", root, name);
     new->num_entries = 0;
+    new->populated_entries = 0;
     return new;
 }
 
@@ -53,15 +55,16 @@ static struct pathelem *new_entry(const char *root,
 /* Not all systems provide this feature */
 #if defined(DT_DIR) && defined(DT_UNKNOWN) && defined(DT_LNK)
 # define dirent_type(dirent) ((dirent)->d_type)
-# define is_dir_maybe(type) \
-    ((type) == DT_DIR || (type) == DT_UNKNOWN || (type) == DT_LNK)
+# define is_not_dir(type) \
+    ((type) != DT_DIR && (type) != DT_UNKNOWN && (type) != DT_LNK)
 #else
 # define dirent_type(dirent) (1)
-# define is_dir_maybe(type)  (type)
+# define is_not_dir(type)  (0)
 #endif
 
 static struct pathelem *add_dir_maybe(struct pathelem *path)
 {
+    unsigned int i;
     DIR *dir;
 
     if ((dir = opendir(path->pathname)) != NULL) {
@@ -74,6 +77,11 @@ static struct pathelem *add_dir_maybe(struct pathelem *path)
         }
         closedir(dir);
     }
+
+    for (i = 0; i < path->num_entries; i++)
+        (path->entries[i])->parent = path;
+
+    path->populated_entries = 1;
     return path;
 }
 
@@ -89,26 +97,16 @@ static struct pathelem *add_entry(struct pathelem *root, const char *name,
     e = &root->entries[root->num_entries-1];
 
     *e = new_entry(root->pathname, root, name);
-    if (is_dir_maybe(type)) {
-        *e = add_dir_maybe(*e);
+    if (is_not_dir(type)) {
+        (*e)->populated_entries = 1;
     }
 
     return root;
 }
 
-/* This needs to be done after tree is stabilized (ie. no more reallocs!). */
-static void set_parents(struct pathelem *child, struct pathelem *parent)
-{
-    unsigned int i;
-
-    child->parent = parent;
-    for (i = 0; i < child->num_entries; i++)
-        set_parents(child->entries[i], child);
-}
-
 /* FIXME: Doesn't handle DIR/.. where DIR is not in emulated dir. */
 static const char *
-follow_path(const struct pathelem *cursor, const char *name)
+follow_path(struct pathelem *cursor, struct pathelem **source, const char *name)
 {
     unsigned int i, namelen;
 
@@ -119,14 +117,18 @@ follow_path(const struct pathelem *cursor, const char *name)
         return cursor->pathname;
 
     if (strneq(name, namelen, ".."))
-        return follow_path(cursor->parent, name + namelen);
+        return follow_path(cursor->parent, &cursor->parent, name + namelen);
 
     if (strneq(name, namelen, "."))
-        return follow_path(cursor, name + namelen);
+        return follow_path(cursor, source, name + namelen);
+
+    if (!cursor->populated_entries)
+        *source = add_dir_maybe(cursor);
+        cursor = *source;
 
     for (i = 0; i < cursor->num_entries; i++)
         if (strneq(name, namelen, cursor->entries[i]->name))
-            return follow_path(cursor->entries[i], name + namelen);
+            return follow_path(cursor->entries[i], &cursor->entries[i], name + namelen);
 
     /* Not found */
     return NULL;
@@ -160,8 +162,6 @@ void init_paths(const char *prefix)
         g_free(base->name);
         g_free(base);
         base = NULL;
-    } else {
-        set_parents(base, base);
     }
 }
 
@@ -173,5 +173,5 @@ const char *path(const char *name)
     if (!base || !name || name[0] != '/')
         return name;
 
-    return follow_path(base, name) ?: name;
+    return follow_path(base, &base, name) ?: name;
 }
