tree-walk: harden make_traverse_path() length computations
The make_traverse_path() function isn't very careful about checking its
output buffer boundaries. In fact, it doesn't even _know_ the size of
the buffer it's writing to, and just assumes that the caller used
traverse_path_len() correctly. And even then we assume that our
traverse_info.pathlen components are all correct, and just blindly write
into the buffer.
Let's improve this situation a bit:
- have the caller pass in their allocated buffer length, which we'll
check against our own computations
- check for integer underflow as we do our backwards-insertion of
pathnames into the buffer
- check that we do not run out items in our list to traverse before
we've filled the expected number of bytes
None of these should be triggerable in practice (especially since our
switch to size_t everywhere in a previous commit), but it doesn't hurt
to check our assumptions.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/tree-walk.c b/tree-walk.c
index c2952f3..4f1e9d7 100644
--- a/tree-walk.c
+++ b/tree-walk.c
@@ -181,21 +181,32 @@
info->prev = &dummy;
}
-char *make_traverse_path(char *path, const struct traverse_info *info,
+char *make_traverse_path(char *path, size_t pathlen,
+ const struct traverse_info *info,
const char *name, size_t namelen)
{
- size_t pathlen = info->pathlen;
+ /* Always points to the end of the name we're about to add */
+ size_t pos = st_add(info->pathlen, namelen);
- path[pathlen + namelen] = 0;
+ if (pos >= pathlen)
+ BUG("too small buffer passed to make_traverse_path");
+
+ path[pos] = 0;
for (;;) {
- memcpy(path + pathlen, name, namelen);
- if (!pathlen)
+ if (pos < namelen)
+ BUG("traverse_info pathlen does not match strings");
+ pos -= namelen;
+ memcpy(path + pos, name, namelen);
+
+ if (!pos)
break;
- path[--pathlen] = '/';
+ path[--pos] = '/';
+
+ if (!info)
+ BUG("traverse_info ran out of list items");
name = info->name;
namelen = info->namelen;
info = info->prev;
- pathlen -= namelen;
}
return path;
}
@@ -207,7 +218,8 @@
size_t len = traverse_path_len(info, namelen);
strbuf_grow(out, len);
- make_traverse_path(out->buf + out->len, info, name, namelen);
+ make_traverse_path(out->buf + out->len, out->alloc - out->len,
+ info, name, namelen);
strbuf_setlen(out, out->len + len);
}
diff --git a/tree-walk.h b/tree-walk.h
index 994c14a..a3ad54e 100644
--- a/tree-walk.h
+++ b/tree-walk.h
@@ -70,7 +70,7 @@
};
int get_tree_entry(const struct object_id *, const char *, struct object_id *, unsigned short *);
-char *make_traverse_path(char *path, const struct traverse_info *info,
+char *make_traverse_path(char *path, size_t pathlen, const struct traverse_info *info,
const char *name, size_t namelen);
void strbuf_make_traverse_path(struct strbuf *out,
const struct traverse_info *info,
diff --git a/unpack-trees.c b/unpack-trees.c
index c3059c2..65c4677 100644
--- a/unpack-trees.c
+++ b/unpack-trees.c
@@ -968,7 +968,8 @@
ce->ce_flags = create_ce_flags(stage);
ce->ce_namelen = len;
oidcpy(&ce->oid, &n->oid);
- make_traverse_path(ce->name, info, n->path, n->pathlen);
+ /* len+1 because the cache_entry allocates space for NUL */
+ make_traverse_path(ce->name, len + 1, info, n->path, n->pathlen);
return ce;
}
