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+/*++
+/* NAME
+/* mail_open_ok 3
+/* SUMMARY
+/* scrutinize mail queue file
+/* SYNOPSIS
+/* #include <mail_open_ok.h>
+/*
+/* int mail_open_ok(queue_name, queue_id, statp, pathp)
+/* const char *queue_name;
+/* const char *queue_id;
+/* struct stat *statp;
+/* char **pathp
+/* DESCRIPTION
+/* mail_open_ok() determines if it is OK to open the specified
+/* queue file.
+/*
+/* The queue name and queue id should conform to the syntax
+/* requirements for these names.
+/* Unfortunately, on some systems readdir() etc. can return bogus
+/* file names. For this reason, the code silently ignores invalid
+/* queue file names.
+/*
+/* The file should have mode 0700. Files with other permissions
+/* are silently ignored.
+/*
+/* The file should be a regular file.
+/* Files that do not satisfy this requirement are skipped with
+/* a warning.
+/*
+/* The file link count is not restricted. With a writable maildrop
+/* directory, refusal to deliver linked files is prone to denial of
+/* service attack; it's better to deliver mail too often than not.
+/*
+/* Upon return, the \fIstatp\fR argument receives the file
+/* attributes and \fIpathp\fR a copy of the file name. The file
+/* name is volatile. Make a copy if it is to be used for any
+/* appreciable amount of time.
+/* DIAGNOSTICS
+/* Warnings: bad file attributes (file type), multiple hard links.
+/* mail_open_ok() returns MAIL_OPEN_YES for good files, MAIL_OPEN_NO
+/* for anything else. It is left up to the system administrator to
+/* deal with non-file objects.
+/* BUGS
+/* mail_open_ok() examines a queue file without actually opening
+/* it, and therefore is susceptible to race conditions.
+/* LICENSE
+/* .ad
+/* .fi
+/* The Secure Mailer license must be distributed with this software.
+/* AUTHOR(S)
+/* Wietse Venema
+/* IBM T.J. Watson Research
+/* P.O. Box 704
+/* Yorktown Heights, NY 10598, USA
+/*--*/
+
+/* System libraries. */
+
+#include <sys_defs.h>
+#include <sys/stat.h>
+#include <time.h>
+#include <errno.h>
+
+/* Utility library. */
+
+#include <msg.h>
+#include <warn_stat.h>
+
+/* Global library. */
+
+#include "mail_queue.h"
+#include "mail_open_ok.h"
+
+/* mail_open_ok - see if this file is OK to open */
+
+int mail_open_ok(const char *queue_name, const char *queue_id,
+ struct stat * statp, const char **path)
+{
+ if (mail_queue_name_ok(queue_name) == 0) {
+ msg_warn("bad mail queue name: %s", queue_name);
+ return (MAIL_OPEN_NO);
+ }
+ if (mail_queue_id_ok(queue_id) == 0)
+ return (MAIL_OPEN_NO);
+
+
+ /*
+ * I really would like to look up the file attributes *after* opening the
+ * file so that we could save one directory traversal on systems without
+ * name-to-inode cache. However, we don't necessarily always want to open
+ * the file.
+ */
+ *path = mail_queue_path((VSTRING *) 0, queue_name, queue_id);
+
+ if (lstat(*path, statp) < 0) {
+ if (errno != ENOENT)
+ msg_warn("%s: %m", *path);
+ return (MAIL_OPEN_NO);
+ }
+ if (!S_ISREG(statp->st_mode)) {
+ msg_warn("%s: uid %ld: not a regular file", *path, (long) statp->st_uid);
+ return (MAIL_OPEN_NO);
+ }
+ if ((statp->st_mode & S_IRWXU) != MAIL_QUEUE_STAT_READY)
+ return (MAIL_OPEN_NO);
+
+ /*
+ * Workaround for spurious "file has 2 links" warnings in showq. As
+ * kernels have evolved from non-interruptible system calls towards
+ * fine-grained locks, the showq command has become likely to observe a
+ * file while the queue manager is in the middle of renaming it, at a
+ * time when the file has links to both the old and new name. We now log
+ * the warning only when the condition appears to be persistent.
+ */
+#define MINUTE_SECONDS 60 /* XXX should be centralized */
+
+ if (statp->st_nlink > 1) {
+ if (msg_verbose)
+ msg_info("%s: uid %ld: file has %d links", *path,
+ (long) statp->st_uid, (int) statp->st_nlink);
+ else if (statp->st_ctime < time((time_t *) 0) - MINUTE_SECONDS)
+ msg_warn("%s: uid %ld: file has %d links", *path,
+ (long) statp->st_uid, (int) statp->st_nlink);
+ }
+ return (MAIL_OPEN_YES);
+}