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.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

2 files changed, 138 insertions, 0 deletions

diff --git a/meta/recipes-devtools/qemu/qemu/pathlimit.patch b/meta/recipes-devtools/qemu/qemu/pathlimit.patch
new file mode 100644
index 0000000000..57ab981c61
--- /dev/null
+++ b/meta/recipes-devtools/qemu/qemu/pathlimit.patch
@@ -0,0 +1,137 @@
+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
+
+Index: qemu-2.5.0/util/path.c
+===================================================================
+--- qemu-2.5.0.orig/util/path.c
++++ qemu-2.5.0/util/path.c
+@@ -19,6 +19,7 @@ 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;
+@@ -49,6 +50,7 @@ static struct pathelem *new_entry(const
+     new->name = g_strdup(name);
+     new->pathname = g_strdup_printf("%s/%s", root, name);
+     new->num_entries = 0;
++    new->populated_entries = 0;
+     return new;
+ }
+ 
+@@ -57,15 +59,16 @@ static struct pathelem *new_entry(const
+ /* 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) {
+@@ -78,6 +81,11 @@ static struct pathelem *add_dir_maybe(st
+         }
+         closedir(dir);
+     }
++
++    for (i = 0; i < path->num_entries; i++)
++        (path->entries[i])->parent = path;
++
++    path->populated_entries = 1;
+     return path;
+ }
+ 
+@@ -93,26 +101,16 @@ static struct pathelem *add_entry(struct
+     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;
+ 
+@@ -123,14 +121,18 @@ follow_path(const struct pathelem *curso
+         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;
+@@ -164,8 +166,6 @@ void init_paths(const char *prefix)
+         g_free(base->name);
+         g_free(base);
+         base = NULL;
+-    } else {
+-        set_parents(base, base);
+     }
+ }
+ 
+@@ -177,5 +177,5 @@ 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;
+ }
diff --git a/meta/recipes-devtools/qemu/qemu_2.5.0.bb b/meta/recipes-devtools/qemu/qemu_2.5.0.bb
index 4398a18b02..e9d9a8dce7 100644
--- a/meta/recipes-devtools/qemu/qemu_2.5.0.bb
+++ b/meta/recipes-devtools/qemu/qemu_2.5.0.bb
@@ -10,6 +10,7 @@ SRC_URI += "file://configure-fix-Darwin-target-detection.patch \
             file://CVE-2016-1568.patch \
             file://CVE-2016-2197.patch \
             file://CVE-2016-2198.patch \
+            file://pathlimit.patch \
            "
 SRC_URI_prepend = "http://wiki.qemu-project.org/download/${BP}.tar.bz2"
 SRC_URI[md5sum] = "f469f2330bbe76e3e39db10e9ac4f8db"