Adding upstream version 3.5.24.upstream/3.5.24upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 353 insertions, 0 deletions

diff --git a/src/util/edit_file.c b/src/util/edit_file.c
new file mode 100644
index 0000000..a7c1059
--- /dev/null
+++ b/src/util/edit_file.c
@@ -0,0 +1,353 @@
+/*++
+/* NAME
+/*	edit_file 3
+/* SUMMARY
+/*	simple cooperative file updating protocol
+/* SYNOPSIS
+/*	#include <edit_file.h>
+/*
+/*	typedef struct {
+/* .in +4
+/*		char	*tmp_path;	/* temp. pathname */
+/*		VSTREAM *tmp_fp;	/* temp. stream */
+/*		/* private members... */
+/* .in -4
+/*	} EDIT_FILE;
+/*
+/*	EDIT_FILE *edit_file_open(original_path, output_flags, output_mode)
+/*	const char *original_path;
+/*	int	output_flags;
+/*	mode_t	output_mode;
+/*
+/*	int	edit_file_close(edit_file)
+/*	EDIT_FILE *edit_file;
+/*
+/*	void	edit_file_cleanup(edit_file)
+/*	EDIT_FILE *edit_file;
+/* DESCRIPTION
+/*	This module implements a simple protocol for cooperative
+/*	processes to update one file. The idea is to 1) create a
+/*	new file under a deterministic temporary pathname, 2)
+/*	populate the new file with updated information, and 3)
+/*	rename the new file into the place of the original file.
+/*	This module provides 1) and 3), and leaves 2) to the
+/*	application. The temporary pathname is deterministic to
+/*	avoid accumulation of thrash after program crashes.
+/*
+/*	edit_file_open() implements the first phase of the protocol.
+/*	It creates or opens an output file with a deterministic
+/*	temporary pathname, obtained by appending the suffix defined
+/*	with EDIT_FILE_SUFFIX to the specified original file pathname.
+/*	The original file itself is not opened.  edit_file_open()
+/*	then locks the output file for exclusive access, and verifies
+/*	that the file still exists under the temporary pathname.
+/*	At this point in the protocol, the current process controls
+/*	both the output file content and its temporary pathname.
+/*
+/*	In the second phase, the application opens the original
+/*	file if needed, and updates the output file via the
+/*	\fBtmp_fp\fR member of the EDIT_FILE data structure.  This
+/*	phase is not implemented by the edit_file() module.
+/*
+/*	edit_file_close() implements the third and final phase of
+/*	the protocol.  It flushes the output file to persistent
+/*	storage, and renames the output file from its temporary
+/*	pathname into the place of the original file. When any of
+/*	these operations fails, edit_file_close() behaves as if
+/*	edit_file_cleanup() was called. Regardless of whether these
+/*	operations succeed, edit_file_close() releases the exclusive
+/*	lock, closes the output file, and frees up memory that was
+/*	allocated by edit_file_open().
+/*
+/*	edit_file_cleanup() aborts the protocol. It discards the
+/*	output file, releases the exclusive lock, closes the output
+/*	file, and frees up memory that was allocated by edit_file_open().
+/*
+/*	Arguments:
+/* .IP original_path
+/*	The pathname of the original file that will be replaced by
+/*	the output file. The temporary pathname for the output file
+/*	is obtained by appending the suffix defined with EDIT_FILE_SUFFIX
+/*	to a copy of the specified original file pathname, and is
+/*	made available via the \fBtmp_path\fR member of the EDIT_FILE
+/*	data structure.
+/* .IP output_flags
+/*	Flags for opening the output file. These are as with open(2),
+/*	except that the O_TRUNC flag is ignored.  edit_file_open()
+/*	always truncates the output file after it has obtained
+/*	exclusive control over the output file content and temporary
+/*	pathname.
+/* .IP output_mode
+/*	Permissions for the output file. These are as with open(2),
+/*	except that the output file is initially created with no
+/*	group or other access permissions. The specified output
+/*	file permissions are applied by edit_file_close().
+/* .IP edit_file
+/*	Pointer to data structure that is returned upon successful
+/*	completion by edit_file_open(), and that must be passed to
+/*	edit_file_close() or edit_file_cleanup().
+/* DIAGNOSTICS
+/*	Fatal errors: memory allocation failure, fstat() failure,
+/*	unlink() failure, lock failure, ftruncate() failure.
+/*
+/*	edit_file_open() immediately returns a null pointer when
+/*	it cannot open the output file.
+/*
+/*	edit_file_close() returns zero on success, VSTREAM_EOF on
+/*	failure.
+/*
+/*	With both functions, the global errno variable indicates
+/*	the nature of the problem.  All errors are relative to the
+/*	temporary output's pathname. With both functions, this
+/*	pathname is not available via the EDIT_FILE data structure,
+/*	because that structure was already destroyed, or not created.
+/* BUGS
+/*	In the non-error case, edit_file_open() will not return
+/*	until it obtains exclusive control over the output file
+/*	content and temporary pathname.  Applications that are
+/*	concerned about deadlock should protect the edit_file_open()
+/*	call with a watchdog timer.
+/*
+/*	When interrupted, edit_file_close() may leave behind a
+/*	world-readable output file under the temporary pathname.
+/*	On some systems this can be used to inflict a shared-lock
+/*	DOS on the protocol.  Applications that are concerned about
+/*	maximal safety should protect the edit_file_close() call
+/*	with sigdelay() and sigresume() calls, but this introduces
+/*	the risk that the program will get stuck forever.
+/* LICENSE
+/* .ad
+/* .fi
+/*	The Secure Mailer license must be distributed with this software.
+/* AUTHOR(S)
+/*	Based on code originally by:
+/*	Victor Duchovni
+/*	Morgan Stanley
+/*
+/*	Packaged into one module with minor improvements by:
+/*	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 <stdio.h>			/* rename(2) */
+#include <errno.h>
+
+ /*
+  * This mask selects all permission bits in the st_mode stat data. There is
+  * no portable definition (unlike S_IFMT, which is defined for the file type
+  * bits). For example, BSD / Linux have ALLPERMS, while Solaris has S_IAMB.
+  */
+#define FILE_PERM_MASK \
+	(S_ISUID | S_ISGID | S_ISVTX | S_IRWXU | S_IRWXG | S_IRWXO)
+
+/* Utility Library. */
+
+#include <msg.h>
+#include <vstream.h>
+#include <mymalloc.h>
+#include <stringops.h>
+#include <myflock.h>
+#include <edit_file.h>
+#include <warn_stat.h>
+
+ /*
+  * Do we reuse and truncate an output file that persists after a crash, or
+  * do we unlink it and create a new file?
+  */
+#define EDIT_FILE_REUSE_AFTER_CRASH
+
+ /*
+  * Protocol internals: the temporary file permissions.
+  */
+#define EDIT_FILE_MODE	(S_IRUSR | S_IWUSR)	/* temp file mode */
+
+ /*
+  * Make complex operations more readable. We could use functions, instead.
+  * The main thing is that we keep the _alloc and _free code together.
+  */
+#define EDIT_FILE_ALLOC(ep, path, mode) do { \
+	(ep) = (EDIT_FILE *) mymalloc(sizeof(EDIT_FILE)); \
+	(ep)->final_path = mystrdup(path); \
+	(ep)->final_mode = (mode); \
+	(ep)->tmp_path = concatenate((path), EDIT_FILE_SUFFIX, (char *) 0); \
+	(ep)->tmp_fp = 0; \
+    } while (0)
+
+#define EDIT_FILE_FREE(ep) do { \
+	myfree((ep)->final_path); \
+	myfree((ep)->tmp_path); \
+	myfree((void *) (ep)); \
+    } while (0)
+
+/* edit_file_open - open and lock file with deterministic temporary pathname */
+
+EDIT_FILE *edit_file_open(const char *path, int flags, mode_t mode)
+{
+    struct stat before_lock;
+    struct stat after_lock;
+    int     saved_errno;
+    EDIT_FILE *ep;
+
+    /*
+     * Initialize. Do not bother to optimize for the error case.
+     */
+    EDIT_FILE_ALLOC(ep, path, mode);
+
+    /*
+     * As long as the output file can be opened under the temporary pathname,
+     * this code can loop or block forever.
+     * 
+     * Applications that are concerned about deadlock should protect the
+     * edit_file_open() call with a watchdog timer.
+     */
+    for ( /* void */ ; /* void */ ; (void) vstream_fclose(ep->tmp_fp)) {
+
+	/*
+	 * Try to open the output file under the temporary pathname. This
+	 * succeeds or fails immediately. To avoid creating a shared-lock DOS
+	 * opportunity after we crash, we create the output file with no
+	 * group or other permissions, and set the final permissions at the
+	 * end (this is one reason why we try to get exclusive control over
+	 * the output file instead of the original file). We postpone file
+	 * truncation until we have obtained exclusive control over the file
+	 * content and temporary pathname. If the open operation fails, we
+	 * give up immediately. The caller can retry the call if desirable.
+	 * 
+	 * XXX If we replace the vstream_fopen() call by safe_open(), then we
+	 * should replace the stat() call below by lstat().
+	 */
+	if ((ep->tmp_fp = vstream_fopen(ep->tmp_path, flags & ~(O_TRUNC),
+					EDIT_FILE_MODE)) == 0) {
+	    saved_errno = errno;
+	    EDIT_FILE_FREE(ep);
+	    errno = saved_errno;
+	    return (0);
+	}
+
+	/*
+	 * At this point we may have opened an existing output file that was
+	 * already locked. Try to lock the open file exclusively. This may
+	 * take some time.
+	 */
+	if (myflock(vstream_fileno(ep->tmp_fp), INTERNAL_LOCK,
+		    MYFLOCK_OP_EXCLUSIVE) < 0)
+	    msg_fatal("lock %s: %m", ep->tmp_path);
+
+	/*
+	 * At this point we have an exclusive lock, but some other process
+	 * may have renamed or removed the output file while we were waiting
+	 * for the lock. If that is the case, back out and try again.
+	 */
+	if (fstat(vstream_fileno(ep->tmp_fp), &before_lock) < 0)
+	    msg_fatal("open %s: %m", ep->tmp_path);
+	if (stat(ep->tmp_path, &after_lock) < 0
+	    || before_lock.st_dev != after_lock.st_dev
+	    || before_lock.st_ino != after_lock.st_ino
+#ifdef HAS_ST_GEN
+	    || before_lock.st_gen != after_lock.st_gen
+#endif
+	/* No need to compare st_rdev or st_nlink here. */
+	    ) {
+	    continue;
+	}
+
+	/*
+	 * At this point we have exclusive control over the output file
+	 * content and its temporary pathname (within the rules of the
+	 * cooperative protocol). But wait, there is more.
+	 * 
+	 * There are many opportunies for trouble when opening a pre-existing
+	 * output file. Here are just a few.
+	 * 
+	 * - Victor observes that a system crash in the middle of the
+	 * final-phase rename() operation may result in the output file
+	 * having both the temporary pathname and the final pathname. In that
+	 * case we must not write to the output file.
+	 * 
+	 * - Wietse observes that crashes may also leave the output file in
+	 * other inconsistent states. To avoid permission-related trouble, we
+	 * simply refuse to work with an output file that has the wrong
+	 * temporary permissions. This won't stop the shared-lock DOS if we
+	 * crash after changing the file permissions, though.
+	 * 
+	 * To work around these crash-related problems, remove the temporary
+	 * pathname, back out, and try again.
+	 */
+	if (!S_ISREG(after_lock.st_mode)
+#ifndef EDIT_FILE_REUSE_AFTER_CRASH
+	    || after_lock.st_size > 0
+#endif
+	    || after_lock.st_nlink > 1
+	    || (after_lock.st_mode & FILE_PERM_MASK) != EDIT_FILE_MODE) {
+	    if (unlink(ep->tmp_path) < 0 && errno != ENOENT)
+		msg_fatal("unlink %s: %m", ep->tmp_path);
+	    continue;
+	}
+
+	/*
+	 * Settle the final details.
+	 */
+#ifdef EDIT_FILE_REUSE_AFTER_CRASH
+	if (ftruncate(vstream_fileno(ep->tmp_fp), 0) < 0)
+	    msg_fatal("truncate %s: %m", ep->tmp_path);
+#endif
+	return (ep);
+    }
+}
+
+/* edit_file_cleanup - clean up without completing the protocol */
+
+void    edit_file_cleanup(EDIT_FILE *ep)
+{
+
+    /*
+     * Don't touch the file after we lose the exclusive lock!
+     */
+    if (unlink(ep->tmp_path) < 0 && errno != ENOENT)
+	msg_fatal("unlink %s: %m", ep->tmp_path);
+    (void) vstream_fclose(ep->tmp_fp);
+    EDIT_FILE_FREE(ep);
+}
+
+/* edit_file_close - rename the file into place and and close the file */
+
+int     edit_file_close(EDIT_FILE *ep)
+{
+    VSTREAM *fp = ep->tmp_fp;
+    int     fd = vstream_fileno(fp);
+    int     saved_errno;
+
+    /*
+     * The rename/unlock portion of the protocol is relatively simple. The
+     * only things that really matter here are that we change permissions as
+     * late as possible, and that we rename the file to its final pathname
+     * before we lose the exclusive lock.
+     * 
+     * Applications that are concerned about maximal safety should protect the
+     * edit_file_close() call with sigdelay() and sigresume() calls. It is
+     * not safe for us to call these functions directly, because the calls do
+     * not nest. It is also not nice to force every caller to run with
+     * interrupts turned off.
+     */
+    if (vstream_fflush(fp) < 0
+	|| fchmod(fd, ep->final_mode) < 0
+#ifdef HAS_FSYNC
+	|| fsync(fd) < 0
+#endif
+	|| rename(ep->tmp_path, ep->final_path) < 0) {
+	saved_errno = errno;
+	edit_file_cleanup(ep);
+	errno = saved_errno;
+	return (VSTREAM_EOF);
+    } else {
+	(void) vstream_fclose(ep->tmp_fp);
+	EDIT_FILE_FREE(ep);
+	return (0);
+    }
+}