From 5aa02f98685d78666293149087d3f69b97528cfb Mon Sep 17 00:00:00 2001 From: Jeff King Date: Wed, 31 Jul 2019 00:38:25 -0400 Subject: [PATCH] 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 Signed-off-by: Junio C Hamano --- tree-walk.c | 28 ++++++++++++++++++++-------- tree-walk.h | 2 +- unpack-trees.c | 3 ++- 3 files changed, 23 insertions(+), 10 deletions(-) diff --git a/tree-walk.c b/tree-walk.c index c2952f3793..4f1e9d79ab 100644 --- a/tree-walk.c +++ b/tree-walk.c @@ -181,21 +181,32 @@ void setup_traverse_info(struct traverse_info *info, const char *base) 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 @@ void strbuf_make_traverse_path(struct strbuf *out, 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 994c14a499..a3ad54e6ce 100644 --- a/tree-walk.h +++ b/tree-walk.h @@ -70,7 +70,7 @@ struct traverse_info { }; 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 c3059c2440..65c4677578 100644 --- a/unpack-trees.c +++ b/unpack-trees.c @@ -968,7 +968,8 @@ static struct cache_entry *create_ce_entry(const struct traverse_info *info, 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; } -- 2.11.4.GIT