On Fri, Sep 06, 2019 at 02:35:03AM -0400, Jeff King wrote: > > Fair enough. Forcing later users to reattempt parsing (and failing > > the same way) would be safer and it should also be sufficient as we > > are talking about how to handle a broken repository, i.e. an error > > case. > > One of the tricky things, and the reason I used a "corrupt" flag in my > earlier sketch, is that the state after we encounter a parse error is > unknown. So imagine parse_commit_buffer() sees that one of the parent > lines is bogus, and we return an error. The caller gets to see whatever > half-parsed state we managed to come up with. > > So far so good. But now imagine we call parse_commit_buffer() again, and > we re-parse. How does that interact with the half-parsed state? Some of > it works OK (e.g., lookup_tree() would find the same tree). Some not so > much (I think we'd keep appending parents at each call). > > I guess this might not be too bad to handle. Value fields like > timestamp_t are OK to overwrite. Pointers to objects likewise, since the > memory is owned elsewhere. If we see existing parent pointers in an > object we're parsing, we could probably free them under the assumption > they're leftover cruft. Likewise for the "tag" field of "struct tag", > which is owned by the struct and should be freed. > > Blobs and trees don't actually parse anything into their structs. So > it's really just special-casing those two items.
So here's something a bit more concrete to play with. Using the patch below, we maintain the invariant that if you called parse_commit() or equivalent and got a successful return, then commit->tree is always non-NULL. That fixes the second "missing tree" test from elsewhere in this thread: https://public-inbox.org/git/042a8ba8b2a98c269f9cd1a8e88488b80d686f0d.1567720960.git...@ttaylorr.com/ _without_ applying the third patch (though the error message we expect in the test does not tweaked). And it likely also protects most of the other callers of get_commit_tree_oid(), assuming somewhere in their code path they call parse_commit() and actually check the error code. Likewise, tag->tagged is always non-NULL after a successful tag parse, which should fix the segfault discussed recently in: https://public-inbox.org/git/20190824230944.ga14...@jessup.stsp.name/ as well as probably others. And callers are still able to view the broken objects, but they have to ignore the error return from the parse functions. This seems like a promising direction. I'd probably break it into a few separate patches, and it would be nice to have some tests (especially one where we actually do try to parse multiple times). --- diff --git a/commit.c b/commit.c index a98de16e3d..47e36fd13e 100644 --- a/commit.c +++ b/commit.c @@ -398,20 +398,37 @@ int parse_commit_buffer(struct repository *r, struct commit *item, const void *b struct object_id parent; struct commit_list **pptr; struct commit_graft *graft; + struct tree *tree; const int tree_entry_len = the_hash_algo->hexsz + 5; const int parent_entry_len = the_hash_algo->hexsz + 7; if (item->object.parsed) return 0; - item->object.parsed = 1; + + if (item->parents) { + /* + * Presumably this is leftover from an earlier failed parse; + * clear it out in preparation for us re-parsing (we'll hit the + * same error, but that's good, since it lets our caller know + * the result cannot be trusted. + */ + free_commit_list(item->parents); + item->parents = NULL; + } + tail += size; if (tail <= bufptr + tree_entry_len + 1 || memcmp(bufptr, "tree ", 5) || bufptr[tree_entry_len] != '\n') return error("bogus commit object %s", oid_to_hex(&item->object.oid)); if (get_oid_hex(bufptr + 5, &parent) < 0) return error("bad tree pointer in commit %s", oid_to_hex(&item->object.oid)); - set_commit_tree(item, lookup_tree(r, &parent)); + tree = lookup_tree(r, &parent); + if (!tree) + return error("bad tree pointer %s in commit %s", + oid_to_hex(&parent), + oid_to_hex(&item->object.oid)); + set_commit_tree(item, tree); bufptr += tree_entry_len + 1; /* "tree " + "hex sha1" + "\n" */ pptr = &item->parents; @@ -450,6 +467,7 @@ int parse_commit_buffer(struct repository *r, struct commit *item, const void *b if (check_graph) load_commit_graph_info(r, item); + item->object.parsed = 1; return 0; } diff --git a/tag.c b/tag.c index 5db870edb9..3dcebb4715 100644 --- a/tag.c +++ b/tag.c @@ -141,7 +141,11 @@ int parse_tag_buffer(struct repository *r, struct tag *item, const void *data, u if (item->object.parsed) return 0; - item->object.parsed = 1; + + if (item->tag) { + /* Left over from an earlier failed parse */ + FREE_AND_NULL(item->tag); + } if (size < the_hash_algo->hexsz + 24) return -1; @@ -167,10 +171,15 @@ int parse_tag_buffer(struct repository *r, struct tag *item, const void *data, u } else if (!strcmp(type, tag_type)) { item->tagged = (struct object *)lookup_tag(r, &oid); } else { - error("Unknown type %s", type); - item->tagged = NULL; + return error("unknown tag type '%s' in %s", + type, oid_to_hex(&item->object.oid)); } + if (!item->tagged) + return error("bad tag pointer to %s in %s", + oid_to_hex(&oid), + oid_to_hex(&item->object.oid)); + if (bufptr + 4 < tail && starts_with(bufptr, "tag ")) ; /* good */ else @@ -187,6 +196,7 @@ int parse_tag_buffer(struct repository *r, struct tag *item, const void *data, u else item->date = 0; + item->object.parsed = 1; return 0; }
