1 files changed, 406 insertions, 0 deletions
diff --git a/src/lib/nfs-workarounds.c b/src/lib/nfs-workarounds.c
new file mode 100644
index 0000000..4bbea8a
--- /dev/null
+++ b/src/lib/nfs-workarounds.c
@@ -0,0 +1,406 @@
+/* Copyright (c) 2006-2018 Dovecot authors, see the included COPYING file */
+
+/*
+   These tests were done with various Linux 2.6 kernels, FreeBSD 6.2 and
+   Solaris 8 and 10.
+
+   Attribute cache is usually flushed with chown()ing or fchown()ing the file.
+   The safest way would be to use uid=-1 gid=-1, but this doesn't work with
+   Linux (it does with FreeBSD 6.2 and Solaris). So we'll first get the
+   file's owner and use it. As long as we're not root the file's owner can't
+   change accidentally. If would be possible to also use chmod()/fchmod(), but
+   that's riskier since it could actually cause an unwanted change.
+
+   Write cache can be flushed with fdatasync(). It's all we need, but other
+   tested alternatives are: fcntl locking (Linux 2.6, Solaris),
+   fchown() (Solaris) and dup()+close() (Linux 2.6, Solaris).
+
+   Read cache flushing is more problematic. There's no universal way to do it.
+   The working methods are:
+
+   Linux 2.6: fcntl(), O_DIRECT
+   Solaris: fchown(), fcntl(), dup()+close()
+   FreeBSD 6.2: fchown()
+
+   fchown() can be easily used for Solaris and FreeBSD, but Linux requires
+   playing with locks. O_DIRECT requires CONFIG_NFS_DIRECTIO to be enabled, so
+   we can't always use it.
+*/
+
+#include "lib.h"
+#include "path-util.h"
+#include "nfs-workarounds.h"
+
+#include <fcntl.h>
+#include <unistd.h>
+#include <sys/stat.h>
+
+#if defined (__linux__) || defined(__sun)
+#  define READ_CACHE_FLUSH_FCNTL
+#endif
+#if defined(__FreeBSD__) || defined(__sun)
+#  define ATTRCACHE_FLUSH_CHOWN_UID_1
+#endif
+
+static void nfs_flush_file_handle_cache_parent_dir(const char *path);
+
+static int
+nfs_safe_do(const char *path, int (*callback)(const char *path, void *context),
+	    void *context)
+{
+        unsigned int i;
+	int ret;
+
+        for (i = 1;; i++) {
+		ret = callback(path, context);
+                if (ret == 0 || errno != ESTALE || i == NFS_ESTALE_RETRY_COUNT)
+                        break;
+
+                /* ESTALE: Some operating systems may fail with this if they
+		   can't internally revalidate the NFS file handle. Flush the
+		   file handle and try again */
+		nfs_flush_file_handle_cache(path);
+        }
+        return ret;
+}
+
+struct nfs_safe_open_context {
+	int flags;
+	int fd;
+};
+
+static int nfs_safe_open_callback(const char *path, void *context)
+{
+	struct nfs_safe_open_context *ctx = context;
+
+	ctx->fd = open(path, ctx->flags);
+	return ctx->fd == -1 ? -1 : 0;
+}
+
+int nfs_safe_open(const char *path, int flags)
+{
+	struct nfs_safe_open_context ctx;
+
+        i_assert((flags & O_CREAT) == 0);
+
+	ctx.flags = flags;
+	if (nfs_safe_do(path, nfs_safe_open_callback, &ctx) < 0)
+		return -1;
+
+	return ctx.fd;
+}
+
+static int nfs_safe_stat_callback(const char *path, void *context)
+{
+	struct stat *buf = context;
+
+	return stat(path, buf);
+}
+
+int nfs_safe_stat(const char *path, struct stat *buf)
+{
+	return nfs_safe_do(path, nfs_safe_stat_callback, buf);
+}
+
+static int nfs_safe_lstat_callback(const char *path, void *context)
+{
+	struct stat *buf = context;
+
+	return lstat(path, buf);
+}
+
+int nfs_safe_lstat(const char *path, struct stat *buf)
+{
+	return nfs_safe_do(path, nfs_safe_lstat_callback, buf);
+}
+
+int nfs_safe_link(const char *oldpath, const char *newpath, bool links1)
+{
+	struct stat st;
+	nlink_t orig_link_count = 1;
+
+	if (!links1) {
+		if (stat(oldpath, &st) < 0)
+			return -1;
+		orig_link_count = st.st_nlink;
+	}
+
+	if (link(oldpath, newpath) == 0) {
+#ifndef __FreeBSD__
+		return 0;
+#endif
+		/* FreeBSD at least up to v6.2 converts EEXIST errors to
+		   success. */
+	} else if (errno != EEXIST)
+		return -1;
+
+	/* We don't know if it succeeded or failed. stat() to make sure. */
+	if (stat(oldpath, &st) < 0)
+		return -1;
+	if (st.st_nlink == orig_link_count) {
+		errno = EEXIST;
+		return -1;
+	}
+	return 0;
+}
+
+static void nfs_flush_chown_uid(const char *path)
+{
+
+#ifdef ATTRCACHE_FLUSH_CHOWN_UID_1
+	uid_t uid = (uid_t)-1;
+	if (chown(path, uid, (gid_t)-1) < 0) {
+		if (errno == ESTALE || errno == EPERM || errno == ENOENT) {
+			/* attr cache is flushed */
+			return;
+		}
+		if (likely(errno == ENOENT)) {
+			nfs_flush_file_handle_cache_parent_dir(path);
+			return;
+		}
+		i_error("nfs_flush_chown_uid: chown(%s) failed: %m", path);
+	}
+#else
+	struct stat st;
+
+	if (stat(path, &st) == 0) {
+		/* do nothing */
+	} else {
+		if (errno == ESTALE) {
+			/* ESTALE causes the OS to flush the attr cache */
+			return;
+		}
+		if (likely(errno == ENOENT)) {
+			nfs_flush_file_handle_cache_parent_dir(path);
+			return;
+		}
+		i_error("nfs_flush_chown_uid: stat(%s) failed: %m", path);
+		return;
+	}
+	/* we use chmod for this operation since chown has been seen to drop S_UID
+	   and S_GID bits from directory inodes in certain conditions */
+	if (chmod(path, st.st_mode & 07777) < 0) {
+		if (errno == EPERM) {
+			/* attr cache is flushed */
+			return;
+		}
+		if (likely(errno == ENOENT)) {
+			nfs_flush_file_handle_cache_parent_dir(path);
+			return;
+		}
+		i_error("nfs_flush_chown_uid: chmod(%s, %04o) failed: %m",
+				path, st.st_mode & 07777);
+	}
+#endif
+}
+
+#ifdef __FreeBSD__
+static bool nfs_flush_fchown_uid(const char *path, int fd)
+{
+	uid_t uid;
+#ifndef ATTRCACHE_FLUSH_CHOWN_UID_1
+	struct stat st;
+
+	if (fstat(fd, &st) < 0) {
+		if (likely(errno == ESTALE))
+			return FALSE;
+		i_error("nfs_flush_attr_cache_fchown: fstat(%s) failed: %m",
+			path);
+		return TRUE;
+	}
+	uid = st.st_uid;
+#else
+	uid = (uid_t)-1;
+#endif
+	if (fchown(fd, uid, (gid_t)-1) < 0) {
+		if (errno == ESTALE)
+			return FALSE;
+		if (likely(errno == EACCES || errno == EPERM)) {
+			/* attr cache is flushed */
+			return TRUE;
+		}
+
+		i_error("nfs_flush_attr_cache_fd_locked: fchown(%s) failed: %m",
+			path);
+	}
+	return TRUE;
+}
+#endif
+
+#ifdef READ_CACHE_FLUSH_FCNTL
+static bool nfs_flush_fcntl(const char *path, int fd)
+{
+	static bool locks_disabled = FALSE;
+	struct flock fl;
+	int ret;
+
+	if (locks_disabled)
+		return FALSE;
+
+	/* If the file was already locked, we'll just get the same lock
+	   again. It should succeed just fine. If was was unlocked, we'll
+	   have to get a lock and then unlock it. Linux 2.6 flushes read cache
+	   only when read/write locking succeeded. */
+	fl.l_type = F_RDLCK;
+	fl.l_whence = SEEK_SET;
+	fl.l_start = 0;
+	fl.l_len = 0;
+
+	alarm(60);
+	ret = fcntl(fd, F_SETLKW, &fl);
+	alarm(0);
+
+	if (unlikely(ret < 0)) {
+		if (errno == ENOLCK) {
+			locks_disabled = TRUE;
+			return FALSE;
+		}
+		i_error("nfs_flush_fcntl: fcntl(%s, F_RDLCK) failed: %m", path);
+		return FALSE;
+	}
+
+	fl.l_type = F_UNLCK;
+	(void)fcntl(fd, F_SETLKW, &fl);
+	return TRUE;
+}
+#endif
+
+void nfs_flush_attr_cache_unlocked(const char *path)
+{
+	int fd;
+
+	/* Try to flush the attribute cache the nice way first. */
+	fd = open(path, O_RDONLY);
+	if (fd != -1)
+		i_close_fd(&fd);
+	else if (errno == ESTALE) {
+		/* this already flushed the cache */
+	} else {
+		/* most likely ENOENT, which means a negative cache hit.
+		   flush the file handles for its parent directory. */
+		nfs_flush_file_handle_cache_parent_dir(path);
+	}
+}
+
+void nfs_flush_attr_cache_maybe_locked(const char *path)
+{
+	nfs_flush_chown_uid(path);
+}
+
+void nfs_flush_attr_cache_fd_locked(const char *path ATTR_UNUSED,
+				    int fd ATTR_UNUSED)
+{
+#ifdef __FreeBSD__
+	/* FreeBSD doesn't flush attribute cache with fcntl(), so we have
+	   to do it ourself. */
+	(void)nfs_flush_fchown_uid(path, fd);
+#else
+	/* Linux and Solaris are fine. */
+#endif
+}
+
+static bool
+nfs_flush_file_handle_cache_dir(const char *path, bool try_parent ATTR_UNUSED)
+{
+#ifdef __linux__
+	/* chown()ing parent is the safest way to handle this */
+	nfs_flush_chown_uid(path);
+#else
+	/* rmdir() is the only choice with FreeBSD and Solaris */
+	if (unlikely(rmdir(path) == 0)) {
+		if (mkdir(path, 0700) == 0) {
+			i_warning("nfs_flush_file_handle_cache_dir: "
+				  "rmdir(%s) unexpectedly "
+				  "removed the dir. recreated.", path);
+		} else {
+			i_warning("nfs_flush_file_handle_cache_dir: "
+				  "rmdir(%s) unexpectedly "
+				  "removed the dir. mkdir() failed: %m", path);
+		}
+	} else if (errno == ESTALE || errno == ENOTDIR ||
+		   errno == ENOTEMPTY || errno == EEXIST || errno == EACCES) {
+		/* expected failures */
+	} else if (errno == ENOENT) {
+		return FALSE;
+	} else if (errno == EINVAL && try_parent) {
+		/* Solaris gives this if we're trying to rmdir() the current
+		   directory. Work around this by temporarily changing the
+		   current directory to the parent directory. */
+		const char *cur_path, *p;
+		int cur_dir_fd;
+		bool ret;
+
+		cur_dir_fd = open(".", O_RDONLY);
+		if (cur_dir_fd == -1) {
+			i_error("open(.) failed for: %m");
+			return TRUE;
+		}
+
+		const char *error;
+		if (t_get_working_dir(&cur_path, &error) < 0) {
+			i_error("nfs_flush_file_handle_cache_dir: %s", error);
+			i_close_fd(&cur_dir_fd);
+			return TRUE;
+		}
+		p = strrchr(cur_path, '/');
+		if (p == NULL)
+			cur_path = "/";
+		else
+			cur_path = t_strdup_until(cur_path, p);
+		if (chdir(cur_path) < 0) {
+			i_error("nfs_flush_file_handle_cache_dir: "
+				"chdir() failed");
+		}
+		ret = nfs_flush_file_handle_cache_dir(path, FALSE);
+		if (fchdir(cur_dir_fd) < 0)
+			i_error("fchdir() failed: %m");
+		i_close_fd(&cur_dir_fd);
+		return ret;
+	} else {
+		i_error("nfs_flush_file_handle_cache_dir: "
+			"rmdir(%s) failed: %m", path);
+	}
+#endif
+	return TRUE;
+}
+
+static void nfs_flush_file_handle_cache_parent_dir(const char *path)
+{
+	const char *p;
+
+	p = strrchr(path, '/');
+	T_BEGIN {
+		if (p == NULL)
+			(void)nfs_flush_file_handle_cache_dir(".", TRUE);
+		else
+			(void)nfs_flush_file_handle_cache_dir(t_strdup_until(path, p),
+							      TRUE);
+	} T_END;
+}
+
+void nfs_flush_file_handle_cache(const char *path)
+{
+	nfs_flush_file_handle_cache_parent_dir(path);
+}
+
+void nfs_flush_read_cache_locked(const char *path ATTR_UNUSED,
+				 int fd ATTR_UNUSED)
+{
+#ifdef READ_CACHE_FLUSH_FCNTL
+	/* already flushed when fcntl() was called */
+#else
+	/* we can only hope that underlying filesystem uses micro/nanosecond
+	   resolution so that attribute cache flushing notices mtime changes */
+	nfs_flush_attr_cache_fd_locked(path, fd);
+#endif
+}
+
+void nfs_flush_read_cache_unlocked(const char *path, int fd)
+{
+#ifdef READ_CACHE_FLUSH_FCNTL
+	if (!nfs_flush_fcntl(path, fd))
+		nfs_flush_attr_cache_fd_locked(path, fd);
+#else
+	nfs_flush_read_cache_locked(path, fd);
+#endif
+}