From: Anicka Bernathova <anicka@anicka.net>
Date: Fri, 29 Aug 2008 15:55:35 +0000 (+0200)
Subject: started work on locking mailboxes
X-Git-Url: http://mj.ucw.cz/gitweb/?a=commitdiff_plain;h=39568271f0cf04774e74e5c403cf1391f81ce2c0;p=umpf.git

started work on locking mailboxes
---

diff --git a/Makefile b/Makefile
index beb1a6e..3597642 100644
--- a/Makefile
+++ b/Makefile
@@ -7,6 +7,8 @@ LDLIBS=-lpcre
 brum: brum.c cond.tab.o int.o lex.o ham.o lists.o
 	gcc -o $@ $^ $(LDLIBS)
 
+lock: lex.o cond.tab.o
+
 cond.tab.o: cond.tab.c lex.o
 
 lex.o: lex.c cond.tab.c
@@ -21,4 +23,4 @@ cond.tab.c: cond.y
 	bison -dvt cond.y
 
 clean:
-	rm -rf cond.tab.[ch] cond.output cond brum *.o
+	rm -rf cond.tab.[ch] cond.output cond brum *.o core
diff --git a/lock.c b/lock.c
new file mode 100644
index 0000000..b7e3ef4
--- /dev/null
+++ b/lock.c
@@ -0,0 +1,159 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#define _GNU_SOURCE
+#include <unistd.h>
+#include <fcntl.h>
+#include <errno.h>
+#include <sys/stat.h>
+
+#include "brum.h"
+
+#define LOCK_MAX_TRIES 30
+
+static void
+random_sleep(unsigned int about, unsigned int offset)
+{
+	int myrand;
+
+	if (about == 0 || offset > about)
+		die("random sleep: Bad input data: %d +- %d", about, offset);
+
+	myrand = random() % offset * (random()%2?1:-1);
+
+	usleep(about * 1000000 + myrand * 500000);
+}
+
+static char*
+cat(char* l, char* r)
+{
+	char* res = xmalloc(strlen(l) + strlen (r) + 1);
+	strcpy(res, l);
+	strcat(res, r);
+
+	return res;	
+}
+
+/* FIXME: what about privileges? */
+static int
+dot_lock(char* path)
+{
+	int i;
+	int fd;
+	int res = -1;
+	char* lockfile = cat(path, ".lock");
+	
+	for (i = 0; i < LOCK_MAX_TRIES; i++){
+		if ((fd = open(lockfile, O_WRONLY | O_EXCL | O_CREAT, 0)) 
+			>= 0) {
+			close(fd);
+			break;
+        	}
+
+		if (errno != EEXIST)
+			break;
+
+		/* FIXME: deal with old locks */
+
+		random_sleep(1, 1);
+	}
+
+	free(lockfile);
+	return res;
+}
+
+static void
+dot_unlock(char* path)
+{
+	char* lockfile = cat(path, ".lock");
+
+	unlink(lockfile);
+
+	free(lockfile);
+}
+
+int
+open_mailbox(char* path, int use_default_mailbox)
+{
+	int fd;
+
+	/* attempt to dot_lock first */
+	if (dot_lock(path))
+		return -1;
+
+	/* if OK, try to open the file:
+		either we are saving to default mailbox (no problem here)
+		or we are saving somewhere else (no need to be privileged)
+	*/	
+	if (use_default_mailbox){
+		/* get our preciousss out of pocket */
+		gid_t ruid, euid, suid;
+		getresgid(&ruid, &euid, &suid);
+		setresgid(ruid, suid, suid);
+
+		/* we are not going to create default mailbox */
+		fd = open(path, O_RDWR);
+		if (fd < 0)
+			return -1;	
+
+		/* hide it again */
+		setresgid(ruid, ruid, suid);
+	} else {
+		fd = open(path, O_RDWR);
+		if (fd < 0 && errno == ENOENT){
+			fd = open(path, O_RDWR | O_CREAT | O_EXCL,
+				S_IRUSR | S_IWUSR);
+			if (fd < 0)
+				return -1;	
+
+		} else if (fd < 0)
+			return -1;	
+	}	
+
+	/* fcntl then */
+	struct flock mb_lock;
+	memset(&mb_lock, 0, sizeof(struct flock));
+	mb_lock.l_type = F_WRLCK;
+	mb_lock.l_whence = SEEK_SET;
+
+	if (fcntl(fd, F_GETLK, &mb_lock) < 0){
+		close(fd);
+		dot_unlock(path);
+		return -1;
+	}
+
+	return fd; 
+}
+
+void
+close_mailbox(int fd, char* path)
+{
+	struct flock mb_lock;
+	memset(&mb_lock, 0, sizeof(struct flock));
+	mb_lock.l_type = F_UNLCK; 
+	fcntl(fd, F_SETLK, &mb_lock);
+	close(fd);
+	dot_unlock(path);
+}
+
+int
+main(int argc, char** argv)
+{
+	/* FIXME: move somewhere */
+	int fd;
+	gid_t ruid, euid, suid;
+	if (argc < 2)
+		return 1;
+	char* mb = argv[1]; 
+	getresgid(&ruid, &euid, &suid);
+	setresgid(ruid, ruid, euid);
+	fd = open_mailbox(mb, 1);
+	printf("%d\n", fd); 
+	if (fd < 0)
+		return 1;	
+
+	close_mailbox(fd, mb);
+
+	return 0;
+}