@matheusbsbs / matheus-bagliano / commits / 670a1dadc7

list-objects: respect max_allowed_tree_depth

The tree traversal in list-objects.c, which is used by "rev-list --objects", etc, uses recursion and may run out of stack space. Let's teach it about the new core.maxTreeDepth config option. We unfortunately can't return an error here, as this code doesn't produce an error return at all. We'll die() instead, which matches the behavior when we see an otherwise broken tree. Note that this will also generally reject such deep trees from entering the repository from a fetch or push, due to the use of rev-list in the connectivity check. But it's not foolproof! We stop traversing when we see an UNINTERESTING object, and the connectivity check marks existing ref tips as UNINTERESTING. So imagine commit X has a tree with maximum depth N. If you then create a new commit Y with a tree entry "Y:subdir" that points to "X^{tree}", then the depth of Y will be N+1. But a connectivity check running "git rev-list --objects Y --not X" won't realize that; it will stop traversing at X^{tree}, since that was already reachable. So this will stop naive pushes of too-deep trees, but not carefully crafted malicious ones. Doing it robustly and efficiently would require caching the maximum depth of each tree (i.e., the longest path to any leaf entry). That's much more complex and not strictly needed. If each recursive algorithm limits itself already, then that's sufficient. Blocking the objects from entering the repo would be a nice belt-and-suspenders addition, but it's not worth the extra cost. Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>

Jeff King committed Aug 31, 2023 at 02:22 UTC 670a1dadc7d98b774cc0f870a4c75f57d1cfa9d4

2 files changed +17

list-objects.c

@@ -14,6 +14,7 @@

14 #include "packfile.h"

15 #include "object-store-ll.h"

16 #include "trace.h"

17 +#include "environment.h"

19 struct traversal_context {

20 struct rev_info *revs;

@@ -21,6 +22,7 @@ struct traversal_context {

22 show_commit_fn show_commit;

23 void *show_data;

24 struct filter *filter;

25 + int depth;

26 };

28 static void show_commit(struct traversal_context *ctx,

@@ -118,7 +120,9 @@ static void process_tree_contents(struct traversal_context *ctx,

120 entry.path, oid_to_hex(&tree->object.oid));

121 }

122 t->object.flags |= NOT_USER_GIVEN;

123 + ctx->depth++;

124 process_tree(ctx, t, base, entry.path);

125 + ctx->depth--;

126 }

127 else if (S_ISGITLINK(entry.mode))

128 ; /* ignore gitlink */

@@ -156,6 +160,9 @@ static void process_tree(struct traversal_context *ctx,

160 !revs->include_check_obj(&tree->object, revs->include_check_data))

161 return;

162

163 + if (ctx->depth > max_allowed_tree_depth)

164 + die("exceeded maximum allowed tree depth");

165 +

166 failed_parse = parse_tree_gently(tree, 1);

167 if (failed_parse) {

168 if (revs->ignore_missing_links)

@@ -349,6 +356,7 @@ static void traverse_non_commits(struct traversal_context *ctx,

356 if (!path)

357 path = "";

358 if (obj->type == OBJ_TREE) {

359 + ctx->depth = 0;

360 process_tree(ctx, (struct tree *)obj, base, path);

361 continue;

362 }

t/t6700-tree-depth.sh

@@ -72,4 +72,13 @@ test_expect_success 'default limit for ls-tree fails gracefully' '

72 test_must_fail git ls-tree -r big >/dev/null

73 '

75 +test_expect_success 'limit recursion of rev-list --objects' '

76 + git $small_ok rev-list --objects small >/dev/null &&

77 + test_must_fail git $small_no rev-list --objects small >/dev/null

78 +'

79 +

80 +test_expect_success 'default limit for rev-list fails gracefully' '

81 + test_must_fail git rev-list --objects big >/dev/null

82 +'

83 +

84 test_done