From: Stefan Sperling <stsp@stsp.name>
Subject: gotwebd segfault fix
To: gameoftrees@openbsd.org
Date: Fri, 9 Aug 2024 09:07:18 +0200

Lucas reported this gotwebd segfault on IRC:

[[[
Program terminated with signal SIGSEGV, Segmentation fault.
#0  0x00000d02d43236b1 in get_path_git_child (repo=0x0, basename=0xd02d42d508d "objects") at /home/got/code/got/gotwebd/../lib/repository.c:178
178     /home/got/code/got/gotwebd/../lib/repository.c: No such file or directory.
(gdb) set max-value-size 131072
(gdb) bt full
#0  0x00000d02d43236b1 in get_path_git_child (repo=0x0, basename=0xd02d42d508d "objects") at /home/got/code/got/gotwebd/../lib/repository.c:178
        path_child = 0xd050000007f <error: Cannot access memory at address 0xd050000007f>
#1  0x00000d02d432366a in got_repo_get_path_objects (repo=0x0) at /home/got/code/got/gotwebd/../lib/repository.c:188
No locals.
#2  0x00000d02d4327f94 in got_repo_match_object_id_prefix (id=0x7f289665fa90, id_str_prefix=0xd059220eba0 "8f6d9a6a62b3640c758a23e26cd567e2e44406e1", obj_type=1, repo=0x0)
    at /home/got/code/got/gotwebd/../lib/repository.c:1965
        err = 0x0
        path_objects = 0x0
        object_dir = 0x0
        len = 1622863644319942746
        i = 3333
#3  0x00000d02d42f1338 in got_get_repo_commits (c=0xd057c2dd000, limit=1) at /home/got/code/got/gotwebd/got_operations.c:354
        error = 0x0
        id = 0x0
        graph = 0x0
        commit = 0x0
        refs = {tqh_first = 0x0, tqh_last = 0x7f289665fa70}
        ref = 0x0
        repo_commit = 0x0
        srv = 0xd04f17be000
        t = 0xd0545d98dc0
        repo = 0x0
]]]

I cut the trace here because the last line shows the problem: t->repo is NULL.

I believe the diff below might fix the issue.

diff /home/stsp/src/got
commit - 7e18255791187735b9e36951caa895974e4e9ba3
path + /home/stsp/src/got
blob - ea44d67c0df8c731d5a45b797add4cbee60f171c
file + gotwebd/gotweb.c
--- gotwebd/gotweb.c
+++ gotwebd/gotweb.c
@@ -1142,12 +1142,15 @@ gotweb_load_got_path(struct repo_dir **rp, const char 
 err:
 	free(dir_test);
 	if (dt != NULL && closedir(dt) == EOF && error == NULL)
 		error = got_error_from_errno("closedir");
 	if (error && t->repo) {
-		got_repo_close(t->repo);
-		t->repo = NULL;
+		/* Some callers proceed doing work in this error case: */
+		if (error->code != GOT_ERR_LONELY_PACKIDX) {
+			got_repo_close(t->repo);
+			t->repo = NULL;
+		}
 	}
 	return error;
 }
 
 static const struct got_error *