1 files changed, 106 insertions, 48 deletions

diff --git a/src/lock.c b/src/lock.c
index eb8a3cb..97dcd49 100644
--- a/src/lock.c
+++ b/src/lock.c
@@ -18,6 +18,11 @@
  * Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA.
  */
 
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#endif
+
+
 #include <unistd.h>
 #include <sys/stat.h>
 #include <stdio.h>
@@ -29,6 +34,7 @@
 #include <string.h>
 #include <assert.h>
 #include <pwd.h>
+#include <inttypes.h>
 
 #include "lock.h"
 #include "util.h"
@@ -40,69 +46,121 @@
 
 static char* lockfile = NULL;
 
-// Tries to lock a TTY-device, returns 0 on success
-int device_lock(char *dev, char *appname) {
-    char buf[256], u[16];
-    char path[PATH_MAX];
+static const char *get_lockfile(const char *dev) {
+    static char lockfile[PATH_MAX];
+    snprintf(lockfile, sizeof(lockfile), "%s/LCK..%s", LOCK_DIR, basename((char*) dev));
+    return lockfile;
+}
+
+static const char *get_tempfile(const char *path) {
+    static char t[PATH_MAX];
+    snprintf(t, sizeof(t), "%s.tmp.%lu", path, (unsigned long) getpid());
+    return t;
+}
+
+
+int device_lock(const char *dev, const char *appname) {
+    struct stat st;
     int fd;
-    struct passwd *pwd;
-    char *username;
+    const char *path, *temp;
+    char buf[100];
+    char uidbuf[32];
 
-    assert(dev && !lockfile);
-    
-    if (access(LOCK_DIR, W_OK) < 0)
+    if (stat(LOCK_DIR, &st) != 0 || !S_ISDIR(st.st_mode)) {
+        fprintf(stderr, "Failed to lock device, directory "LOCK_DIR" not existent.\n");
         return -1;
+    }
+
+    path = get_lockfile(dev);
+    temp = get_tempfile(path);
+
+    for (;;) {
+        mode_t u;
+        struct passwd* pw;
+        char *username;
         
-    snprintf(path, sizeof(path), "%s/LCK..%s", LOCK_DIR, basename(dev));
-      
-    if ((fd = open(path, O_RDONLY)) >= 0) {
-        int n = loop_read(fd, buf, sizeof(buf) - 1);
-        close(fd);
+        if ((fd = open(path, O_RDONLY)) < 0) {
+            if (errno != ENOENT) {
+                fprintf(stderr, "Failed to open lock file: %s\n", strerror(errno));
+                return -1;
+            }
+        }
+        
+        if (fd >= 0) {
+            ssize_t n;
 
-        if (n > 0) {
-            int pid;
-            
-            if (n == 4)
-                pid = *(int*) buf;
-            else {
-                buf[n] = 0;
-                sscanf(buf, "%d", &pid);
+            n = loop_read(fd, buf, sizeof(buf) - 1);
+            close(fd);
+
+            if (n < 0) {
+                close(fd);
+                fprintf(stderr, "Failed to read from lock file: %s\n", strerror(errno));
+                return -1;
             }
-	      
-            if (pid > 0) {
-                if (kill((pid_t) pid, 0) < 0 && errno == ESRCH) {
-                    fprintf(stderr, "Lockfile is stale. Overriding it.\n");
-                    unlink(path);
-                } else
-                    return -1;
+            
+            if (n > 0) {
+                pid_t pid;
+                
+                if (n == 4)
+                    pid = (pid_t) *((uint32_t*) buf);
+                else {
+                    unsigned long v;
+                    buf[n] = 0;
+                    sscanf(buf, "%lu", &v);
+                    pid = (pid_t) v;
+                }
+                
+                if (pid > 0) {
+                    if (kill(pid, 0) < 0 && errno == ESRCH) {
+                        fprintf(stderr, "Lockfile is stale. Overriding it.\n");
+                        /* Yes, here is a race condition */
+                        unlink(path);
+                    } else
+                        return 1;
+                }
             }
         }
-    }
 
-    if ((fd = open(path, O_WRONLY | O_CREAT | O_EXCL, 0666)) < 0)
-        return -1;
-      
-    if ((pwd = getpwuid(getuid())))
-        username = pwd->pw_name;
-    else
-        snprintf(username = u, sizeof(u), "%u", getuid());
+        u = umask(0033);
+        fd = open(temp, O_WRONLY | O_CREAT | O_EXCL, 0666);
+        umask(u);
+        
+        if (fd < 0) {
+            fprintf(stderr, "Failed to create temporary lock file: %s", strerror(errno));
+            return -1;
+        }
+
+        if ((pw = getpwuid(getuid())))
+            username = pw->pw_name;
+        else
+            snprintf(username = uidbuf, sizeof(uidbuf), "%lu", (unsigned long) getuid());
+
+        snprintf(buf, sizeof(buf), "%10lu %s %.20s\n", (unsigned long) getpid(), appname, username);
+        if (loop_write(fd, buf, strlen(buf)) < 0) {
+            fprintf(stderr, "Failed to write to temporary lock file: %s", strerror(errno));
+            close(fd);
+            return -1;
+        }
 
-    snprintf(buf, sizeof(buf), "%10ld %s %.20s\n", (long)getpid(), appname, username);
-    
-    if (loop_write(fd, buf, strlen(buf)) < 0) {
         close(fd);
-        return -1;
-    }
-    
-    close(fd);
 
-    lockfile = strdup(path);
-    
-    return 0;
+        if (link(temp, path) < 0) {
+            if (errno == EEXIST)
+                continue;
+
+            fprintf(stderr, "Failed to link temporary lock file: %s", strerror(errno));
+        }
+
+        unlink(temp);
+        lockfile = strdup(path);
+
+        return 0;
+    }
 }
 
+
 // Tries to lock the first free device, returns 0 on success
-int device_lock_first(char *appname, char *dev, size_t l) {
+int device_lock_first(const char *appname, char *dev, size_t l) {
     int i, found = 0;
 
     for (i = 2; i <= 20; i++) {