Fix cache algorithm loophole

This closes the door for unneccessary calls to cgit_fill_cache().

Noticed by Linus.

Signed-off-by: Lars Hjemli <hjemli@gmail.com>

3 files changed, 16 insertions, 11 deletions

diff --git a/cache.c b/cache.c
index b034c48..0ffa502 100644
--- a/cache.c
+++ b/cache.c
@@ -1,94 +1,98 @@
 /* cache.c: cache management
  *
  * Copyright (C) 2006 Lars Hjemli
  *
  * Licensed under GNU General Public License v2
  *   (see COPYING for full license text)
  */
 
 #include "cgit.h"
 
 const int NOLOCK = -1;
 
-int cache_lookup(struct cacheitem *item)
+void cache_prepare(struct cacheitem *item)
 {
 	if (!cgit_query_repo) {
 		item->name = xstrdup(fmt("%s/index.html", cgit_cache_root));
 		item->ttl = cgit_cache_root_ttl;
 	} else if (!cgit_query_page) {
 		item->name = xstrdup(fmt("%s/%s/index.html", cgit_cache_root, 
 			   cgit_query_repo));
 		item->ttl = cgit_cache_repo_ttl;
 	} else {
 		item->name = xstrdup(fmt("%s/%s/%s/%s.html", cgit_cache_root, 
 			   cgit_query_repo, cgit_query_page, 
 			   cgit_querystring));
 		if (cgit_query_has_symref)
 			item->ttl = cgit_cache_dynamic_ttl;
 		else if (cgit_query_has_sha1)
 			item->ttl = cgit_cache_static_ttl;
 		else
 			item->ttl = cgit_cache_repo_ttl;
 	}
+}
+
+int cache_exist(struct cacheitem *item)
+{
 	if (stat(item->name, &item->st)) {
 		item->st.st_mtime = 0;
 		return 0;
 	}
 	return 1;
 }
 
 int cache_create_dirs()
 {
 	char *path;
 
 	if (!cgit_query_repo)
 		return 0;
 
 	path = fmt("%s/%s", cgit_cache_root, cgit_query_repo);
 	if (mkdir(path, S_IRWXU) && errno!=EEXIST)
 		return 0;
 
 	if (cgit_query_page) {
 		path = fmt("%s/%s/%s", cgit_cache_root, cgit_query_repo, 
 			   cgit_query_page);
 		if (mkdir(path, S_IRWXU) && errno!=EEXIST)
 			return 0;
 	}
 	return 1;
 }
 
 int cache_lock(struct cacheitem *item)
 {
 	int ret;
 	char *lockfile = fmt("%s.lock", item->name);
 
  top:  
        	item->fd = open(lockfile, O_WRONLY | O_CREAT | O_EXCL, S_IRUSR|S_IWUSR);
 	if (item->fd == NOLOCK && errno == ENOENT && cache_create_dirs())
 		goto top;
 	if (item->fd == NOLOCK && errno == EEXIST) {
 		struct stat st;
 		time_t t;
 		if (stat(lockfile, &st))
 			return ret;
 		t = time(NULL);
 		if (t-st.st_mtime > cgit_cache_max_create_time && 
 		    !unlink(lockfile))
 			goto top;
 		return 0;
 	}
 	return (item->fd > 0);
 }
 
 int cache_unlock(struct cacheitem *item)
 {
 	close(item->fd);
 	return (rename(fmt("%s.lock", item->name), item->name) == 0);
 }
 
 int cache_expired(struct cacheitem *item)
 {
 	if (item->ttl < 0)
 		return 0;
 	return item->st.st_mtime + item->ttl * 60 < time(NULL);
 }
diff --git a/cgit.c b/cgit.c
index 110face..7f14016 100644
--- a/cgit.c
+++ b/cgit.c
@@ -276,233 +276,233 @@ static void cgit_print_repolist()
 
 static void cgit_print_branches()
 {
 	html("<table class='list'>");
 	html("<tr><th>Branch name</th><th>Head commit</th></tr>\n");
 	for_each_branch_ref(cgit_print_branch_cb, NULL);
 	html("</table>");
 }
 
 static int get_one_line(char *txt)
 {
 	char *t;
 
 	for(t=txt; *t != '\n' && t != '\0'; t++)
 		;
 	*t = '\0';
 	return t-txt-1;
 }
 
 static void cgit_print_commit_shortlog(struct commit *commit)
 {
 	char *h, *t, *p; 
 	char *tree = NULL, *author = NULL, *subject = NULL;
 	int len;
 	time_t sec;
 	struct tm *time;
 	char buf[32];
 
 	h = t = commit->buffer;
 	
 	if (strncmp(h, "tree ", 5))
 		die("Bad commit format: %s", 
 		    sha1_to_hex(commit->object.sha1));
 	
 	len = get_one_line(h);
 	tree = h+5;
 	h += len + 2;
 
 	while (!strncmp(h, "parent ", 7))
 		h += get_one_line(h) + 2;
 	
 	if (!strncmp(h, "author ", 7)) {
 		author = h+7;
 		h += get_one_line(h) + 2;
 		t = author;
 		while(t!=h && *t!='<') 
 			t++;
 		*t='\0';
 		p = t;
 		while(--t!=author && *t==' ')
 			*t='\0';
 		while(++p!=h && *p!='>')
 			;
 		while(++p!=h && !isdigit(*p))
 			;
 
 		t = p;
 		while(++p && isdigit(*p))
 			;
 		*p = '\0';
 		sec = atoi(t);
 		time = gmtime(&sec);
 	}
 
 	while((len = get_one_line(h)) > 0)
 		h += len+2;
 
 	h++;
 	len = get_one_line(h);
 
 	subject = h;
 
 	html("<tr><td>");
 	strftime(buf, sizeof(buf), "%Y-%m-%d %H:%M:%S", time);
 	html_txt(buf);
 	html("</td><td>");
 	char *qry = fmt("id=%s", sha1_to_hex(commit->object.sha1));
 	char *url = cgit_pageurl(cgit_query_repo, "view", qry);
 	html_link_open(url, NULL, NULL);
 	html_txt(subject);
 	html_link_close();
 	html("</td><td>");
 	html_txt(author);
 	html("</td></tr>\n");
 }
 
 static void cgit_print_log(const char *tip, int ofs, int cnt)
 {
 	struct rev_info rev;
 	struct commit *commit;
 	const char *argv[2] = {NULL, tip};
 	int n = 0;
 	
 	init_revisions(&rev, NULL);
 	rev.abbrev = DEFAULT_ABBREV;
 	rev.commit_format = CMIT_FMT_DEFAULT;
 	rev.verbose_header = 1;
 	rev.show_root_diff = 0;
 	setup_revisions(2, argv, &rev, NULL);
 	prepare_revision_walk(&rev);
 
 	html("<h2>Log</h2>");
 	html("<table class='list'>");
 	html("<tr><th>Date</th><th>Message</th><th>Author</th></tr>\n");
 	while ((commit = get_revision(&rev)) != NULL && n++ < 100) {
 		cgit_print_commit_shortlog(commit);
 		free(commit->buffer);
 		commit->buffer = NULL;
 		free_commit_list(commit->parents);
 		commit->parents = NULL;
 	}
 	html("</table>\n");
 }
 
 static void cgit_print_repo_summary()
 {
 	html("<h2>");
 	html_txt("Repo summary page");
 	html("</h2>");
 	cgit_print_branches();
 }
 
 static void cgit_print_object(char *hex)
 {
 	unsigned char sha1[20];
 	//struct object *object;
 	char type[20];
 	unsigned char *buf;
 	unsigned long size;
 
 	if (get_sha1_hex(hex, sha1)){
 		htmlf(cgit_error, "Bad hex value");
 	        return;
 	}
 
 	if (sha1_object_info(sha1, type, NULL)){
 		htmlf(cgit_error, "Bad object name");
 		return;
 	}
 
 	buf = read_sha1_file(sha1, type, &size);
 	if (!buf) {
 		htmlf(cgit_error, "Error reading object");
 		return;
 	}
 
 	buf[size] = '\0';
 	html("<h2>Object view</h2>");
 	htmlf("sha1=%s<br/>type=%s<br/>size=%i<br/>", hex, type, size);
 	html("<pre>");
 	html_txt(buf);
 	html("</pre>");
 }
 
 static void cgit_print_repo_page()
 {
 	if (chdir(fmt("%s/%s", cgit_root, cgit_query_repo)) || 
 	    cgit_read_config("info/cgit", cgit_repo_config_cb)) {
 		char *title = fmt("%s - %s", cgit_root_title, "Bad request");
 		cgit_print_docstart(title);
 		cgit_print_pageheader(title);
 		htmlf(cgit_lib_error, "Unable to scan repository",
 		      strerror(errno));
 		cgit_print_docend();
 		return;
 	}
 	setenv("GIT_DIR", fmt("%s/%s", cgit_root, cgit_query_repo), 1);
 	char *title = fmt("%s - %s", cgit_repo_name, cgit_repo_desc);
 	cgit_print_docstart(title);
 	cgit_print_pageheader(title);
 	if (!cgit_query_page)
 		cgit_print_repo_summary();
 	else if (!strcmp(cgit_query_page, "log")) {
 		cgit_print_log(cgit_query_head, 0, 100);
 	} else if (!strcmp(cgit_query_page, "view")) {
 		cgit_print_object(cgit_query_sha1);
 	}
 	cgit_print_docend();
 }
 
 static void cgit_fill_cache(struct cacheitem *item)
 {
 	htmlfd = item->fd;
 	item->st.st_mtime = time(NULL);
 	if (cgit_query_repo)
 		cgit_print_repo_page();
 	else
 		cgit_print_repolist();
 }
 
 static void cgit_refresh_cache(struct cacheitem *item)
 {
+	cache_prepare(item);
  top:
-	if (!cache_lookup(item)) {
-		if (cache_lock(item)) {
-			cgit_fill_cache(item);
-			cache_unlock(item);
-		} else {
+	if (!cache_exist(item)) {
+		if (!cache_lock(item)) {
 			sched_yield();
 			goto top;
 		}
-	} else if (cache_expired(item)) {
-		if (cache_lock(item)) {
+		if (!cache_exist(item))
 			cgit_fill_cache(item);
-			cache_unlock(item);
-		}
+		cache_unlock(item);
+	} else if (cache_expired(item) && cache_lock(item)) {
+		if (cache_expired(item))
+			cgit_fill_cache(item);
+		cache_unlock(item);
 	}
 }
 
 static void cgit_print_cache(struct cacheitem *item)
 {
 	static char buf[4096];
 	ssize_t i;
 
 	int fd = open(item->name, O_RDONLY);
 	if (fd<0)
 		die("Unable to open cached file %s", item->name);
 
 	while((i=read(fd, buf, sizeof(buf))) > 0)
 		write(STDOUT_FILENO, buf, i);
 
 	close(fd);
 }
 
 int main(int argc, const char **argv)
 {
 	cgit_read_config("/etc/cgitrc", cgit_global_config_cb);
 	cgit_querystring = xstrdup(getenv("QUERY_STRING"));
 	cgit_parse_query(cgit_querystring, cgit_querystring_cb);
 	cgit_refresh_cache(&cacheitem);
 	cgit_print_cache(&cacheitem);
 	return 0;
 }
diff --git a/cgit.h b/cgit.h
index 1e084d4..3b0994a 100644
--- a/cgit.h
+++ b/cgit.h
@@ -1,64 +1,65 @@
 #ifndef CGIT_H
 #define CGIT_H
 
 #include "git.h"
 #include <openssl/sha.h>
 #include <ctype.h>
 #include <sched.h>
 
 typedef void (*configfn)(const char *name, const char *value);
 
 struct cacheitem {
 	char *name;
 	struct stat st;
 	int ttl;
 	int fd;
 };
 
 extern char *cgit_root;
 extern char *cgit_root_title;
 extern char *cgit_css;
 extern char *cgit_logo;
 extern char *cgit_logo_link;
 extern char *cgit_virtual_root;
 extern char *cgit_cache_root;
 
 extern int cgit_cache_root_ttl;
 extern int cgit_cache_repo_ttl;
 extern int cgit_cache_dynamic_ttl;
 extern int cgit_cache_static_ttl;
 extern int cgit_cache_max_create_time;
 
 extern char *cgit_repo_name;
 extern char *cgit_repo_desc;
 extern char *cgit_repo_owner;
 
 extern int cgit_query_has_symref;
 extern int cgit_query_has_sha1;
 
 extern char *cgit_querystring;
 extern char *cgit_query_repo;
 extern char *cgit_query_page;
 extern char *cgit_query_head;
 extern char *cgit_query_sha1;
 
 extern int htmlfd;
 
 extern char *fmt(const char *format,...);
 
 extern void html(const char *txt);
 extern void htmlf(const char *format,...);
 extern void html_txt(char *txt);
 extern void html_attr(char *txt);
 extern void html_link_open(char *url, char *title, char *class);
 extern void html_link_close(void);
 
 
 extern int cgit_read_config(const char *filename, configfn fn);
 
-extern int cache_lookup(struct cacheitem *item);
+extern void cache_prepare(struct cacheitem *item);
 extern int cache_lock(struct cacheitem *item);
 extern int cache_unlock(struct cacheitem *item);
+extern int cache_exist(struct cacheitem *item);
 extern int cache_expired(struct cacheitem *item);
 
 #endif /* CGIT_H */