[PATCH] show-branch: use strbuf instead of static buffer
- From
Jeff King <peff@peff.net>
- Date
- Apr 5, 2013, 21:15 UTC
- Message-ID
- <20130405211550.GA4880@sigill.intra.peff.net>
When we generate relative names (e.g., "master~20^2"), we format the name into a static buffer, then xstrdup the result to attach it to the commit. Since the first thing we add into the static buffer is the already-computed name of the child commit, the names may get longer and longer as the traversal gets deeper, and we may eventually overflow the fixed-size buffer.
Fix this by converting the fixed-size buffer into a dynamic strbuf. The performance implications should be minimal, as we end up allocating a heap copy of the name anyway (and now we can just detach the heap copy from the strbuf).
Reported-by: Eric Roman <eroman@chromium.org> Signed-off-by: Jeff King <peff@peff.net> --- This is a fix for a bug report that came to me off-list. A real-world example can be seen by running "git show-branch --all" on a fresh clone of:
https://chromium.googlesource.com/chromium/src.git
(but that repo is 1.7G, so I don't recommend cloning it unless you're really interested). Its master branch consists of a strange sequence of merges that results in naming commits like master^2^2^2^2... and so on (it's unclear to me why, but it looks like maybe syncing up separate svn and git repositories?). Which is odd, but looking at graph, I think the names show-branch is generating are correct; they're just really long. And of course odd history is no excuse to overflow a buffer.
Though this is a stack overflow, I don't know that it's exploitable for anything interesting; an attacker does not get to write arbitrary data, but rather only a sequence of "^%d" and "~%d" relative history markers. Perhaps in theory one could devise a history such that the sequence markers spelled out some malicious code, but it would be quite a challenge (and given that you have only ascii [^~0-9] to work with, probably impossible).
I prepared this on "master", but it should be suitable for "maint"; the code dates all the way back to git v0.99.
builtin/show-branch.c | 17 ++++++++--------- 1 file changed, 8 insertions(+), 9 deletions(-)
diff --git a/builtin/show-branch.c b/builtin/show-branch.c index d208fd6..90fc6b1 100644 --- a/builtin/show-branch.c +++ b/builtin/show-branch.c @@ -162,29 +162,28 @@ static void name_commits(struct commit_list *list, nth = 0; while (parents) { struct commit *p = parents->item; - char newname[1000], *en; + struct strbuf newname = STRBUF_INIT; parents = parents->next; nth++; if (p->util) continue; - en = newname; switch (n->generation) { case 0: - en += sprintf(en, "%s", n->head_name); + strbuf_addstr(&newname, n->head_name); break; case 1: - en += sprintf(en, "%s^", n->head_name); + strbuf_addf(&newname, "%s^", n->head_name); break; default: - en += sprintf(en, "%s~%d", - n->head_name, n->generation); + strbuf_addf(&newname, "%s~%d", + n->head_name, n->generation); break; } if (nth == 1) - en += sprintf(en, "^"); + strbuf_addch(&newname, '^'); else - en += sprintf(en, "^%d", nth); - name_commit(p, xstrdup(newname), 0); + strbuf_addf(&newname, "^%d", nth); + name_commit(p, strbuf_detach(&newname, NULL), 0); i++; name_first_parent_chain(p); }
-- 1.8.2.rc0.33.gd915649