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/*++
/* NAME
/* mbox_open 3
/* SUMMARY
/* mailbox access
/* SYNOPSIS
/* #include <mbox_open.h>
/*
/* typedef struct {
/* .in +4
/* /* public members... */
/* VSTREAM *fp;
/* .in -4
/* } MBOX;
/*
/* MBOX *mbox_open(path, flags, mode, st, user, group, lock_style,
/* def_dsn, why)
/* const char *path;
/* int flags;
/* mode_t mode;
/* struct stat *st;
/* uid_t user;
/* gid_t group;
/* int lock_style;
/* const char *def_dsn;
/* DSN_BUF *why;
/*
/* void mbox_release(mbox)
/* MBOX *mbox;
/*
/* const char *mbox_dsn(err, def_dsn)
/* int err;
/* const char *def_dsn;
/* DESCRIPTION
/* This module manages access to UNIX mailbox-style files.
/*
/* mbox_open() acquires exclusive access to the named file.
/* The \fBpath, flags, mode, st, user, group, why\fR arguments
/* are passed to the \fBsafe_open\fR() routine. Attempts to change
/* file ownership will succeed only if the process runs with
/* adequate effective privileges.
/* The \fBlock_style\fR argument specifies a lock style from
/* mbox_lock_mask(). Locks are applied to regular files only.
/* The result is a handle that must be destroyed by mbox_release().
/* The \fBdef_dsn\fR argument is given to mbox_dsn().
/*
/* mbox_release() releases the named mailbox. It is up to the
/* application to close the stream.
/*
/* mbox_dsn() translates an errno value to a mailbox related
/* enhanced status code.
/* .IP "EAGAIN, ESTALE"
/* These result in a 4.2.0 soft error (mailbox problem).
/* .IP ENOSPC
/* This results in a 4.3.0 soft error (mail system full).
/* .IP "EDQUOT, EFBIG"
/* These result in a 5.2.2 hard error (mailbox full).
/* .PP
/* All other errors are assigned the specified default error
/* code. Typically, one would specify 4.2.0 or 5.2.0.
/* DIAGNOSTICS
/* mbox_open() returns a null pointer in case of problems, and
/* sets errno to EAGAIN if someone else has exclusive access.
/* Other errors are likely to have a more permanent nature.
/* 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 library. */
#include <sys_defs.h>
#include <sys/stat.h>
#include <errno.h>
#ifndef EDQUOT
#define EDQUOT EFBIG
#endif
/* Utility library. */
#include <msg.h>
#include <vstream.h>
#include <vstring.h>
#include <safe_open.h>
#include <iostuff.h>
#include <mymalloc.h>
#include <warn_stat.h>
/* Global library. */
#include <dot_lockfile.h>
#include <deliver_flock.h>
#include <mbox_conf.h>
#include <mbox_open.h>
/* mbox_open - open mailbox-style file for exclusive access */
MBOX *mbox_open(const char *path, int flags, mode_t mode, struct stat * st,
uid_t chown_uid, gid_t chown_gid,
int lock_style, const char *def_dsn,
DSN_BUF *why)
{
struct stat local_statbuf;
MBOX *mp;
int locked = 0;
VSTREAM *fp;
if (st == 0)
st = &local_statbuf;
/*
* If this is a regular file, create a dotlock file. This locking method
* does not work well over NFS, but it is better than some alternatives.
* With NFS, creating files atomically is a problem, and a successful
* operation can fail with EEXIST.
*
* If filename.lock can't be created for reasons other than "file exists",
* issue only a warning if the application says it is non-fatal. This is
* for bass-awkward compatibility with existing installations that
* deliver to files in non-writable directories.
*
* We dot-lock the file before opening, so we must avoid doing silly things
* like dot-locking /dev/null. Fortunately, deliveries to non-mailbox
* files execute with recipient privileges, so we don't have to worry
* about creating dotlock files in places where the recipient would not
* be able to write.
*
* Note: we use stat() to follow symlinks, because safe_open() allows the
* target to be a root-owned symlink, and we don't want to create dotlock
* files for /dev/null or other non-file objects.
*/
if ((lock_style & MBOX_DOT_LOCK)
&& (stat(path, st) < 0 || S_ISREG(st->st_mode))) {
if (dot_lockfile(path, why->reason) == 0) {
locked |= MBOX_DOT_LOCK;
} else if (errno == EEXIST) {
dsb_status(why, mbox_dsn(EAGAIN, def_dsn));
return (0);
} else if (lock_style & MBOX_DOT_LOCK_MAY_FAIL) {
msg_warn("%s", vstring_str(why->reason));
} else {
dsb_status(why, mbox_dsn(errno, def_dsn));
return (0);
}
}
/*
* Open or create the target file. In case of a privileged open, the
* privileged user may be attacked with hard/soft link tricks in an
* unsafe parent directory. In case of an unprivileged open, the mail
* system may be attacked by a malicious user-specified path, or the
* unprivileged user may be attacked with hard/soft link tricks in an
* unsafe parent directory. Open non-blocking to fend off attacks
* involving non-file targets.
*/
if ((fp = safe_open(path, flags | O_NONBLOCK, mode, st,
chown_uid, chown_gid, why->reason)) == 0) {
dsb_status(why, mbox_dsn(errno, def_dsn));
if (locked & MBOX_DOT_LOCK)
dot_unlockfile(path);
return (0);
}
close_on_exec(vstream_fileno(fp), CLOSE_ON_EXEC);
/*
* If this is a regular file, acquire kernel locks. flock() locks are not
* intended to work across a network; fcntl() locks are supposed to work
* over NFS, but in the real world, NFS lock daemons often have serious
* problems.
*/
#define HUNKY_DORY(lock_mask, myflock_style) ((lock_style & (lock_mask)) == 0 \
|| deliver_flock(vstream_fileno(fp), (myflock_style), why->reason) == 0)
if (S_ISREG(st->st_mode)) {
if (HUNKY_DORY(MBOX_FLOCK_LOCK, MYFLOCK_STYLE_FLOCK)
&& HUNKY_DORY(MBOX_FCNTL_LOCK, MYFLOCK_STYLE_FCNTL)) {
locked |= lock_style;
} else {
dsb_status(why, mbox_dsn(errno, def_dsn));
if (locked & MBOX_DOT_LOCK)
dot_unlockfile(path);
vstream_fclose(fp);
return (0);
}
}
/*
* Sanity check: reportedly, GNU POP3D creates a new mailbox file and
* deletes the old one. This does not play well with software that opens
* the mailbox first and then locks it, such as software that uses FCNTL
* or FLOCK locks on open file descriptors (some UNIX systems don't use
* dotlock files).
*
* To detect that GNU POP3D deletes the mailbox file we look at the target
* file hard-link count. Note that safe_open() guarantees a hard-link
* count of 1, so any change in this count is a sign of trouble.
*/
if (S_ISREG(st->st_mode)
&& (fstat(vstream_fileno(fp), st) < 0 || st->st_nlink != 1)) {
vstring_sprintf(why->reason, "target file status changed unexpectedly");
dsb_status(why, mbox_dsn(EAGAIN, def_dsn));
msg_warn("%s: file status changed unexpectedly", path);
if (locked & MBOX_DOT_LOCK)
dot_unlockfile(path);
vstream_fclose(fp);
return (0);
}
mp = (MBOX *) mymalloc(sizeof(*mp));
mp->path = mystrdup(path);
mp->fp = fp;
mp->locked = locked;
return (mp);
}
/* mbox_release - release mailbox exclusive access */
void mbox_release(MBOX *mp)
{
/*
* Unfortunately we can't close the stream, because on some file systems
* (AFS), the only way to find out if a file was written successfully is
* to close it, and therefore the close() operation is in the mail_copy()
* routine. If we really insist on owning the vstream member, then we
* should export appropriate methods that mail_copy() can use in order to
* manipulate a message stream.
*/
if (mp->locked & MBOX_DOT_LOCK)
dot_unlockfile(mp->path);
myfree(mp->path);
myfree((void *) mp);
}
/* mbox_dsn - map errno value to mailbox-related DSN detail */
const char *mbox_dsn(int err, const char *def_dsn)
{
#define TRY_AGAIN_ERROR(e) \
(e == EAGAIN || e == ESTALE)
#define SYSTEM_FULL_ERROR(e) \
(e == ENOSPC)
#define MBOX_FULL_ERROR(e) \
(e == EDQUOT || e == EFBIG)
return (TRY_AGAIN_ERROR(err) ? "4.2.0" :
SYSTEM_FULL_ERROR(err) ? "4.3.0" :
MBOX_FULL_ERROR(err) ? "5.2.2" :
def_dsn);
}
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