[libvirt] [PATCH 2/3] New utility functions virFileCreate and virDirCreate
Laine Stump
laine at laine.org
Mon Jan 11 05:46:11 UTC 2010
These functions create a new file or directory with the given
uid/gid. If the flag VIR_FILE_CREATE_AS_UID is given, they do this by
forking a new process, calling setuid/setgid in the new process, and
then creating the file. This is better than simply calling open then
fchown, because in the latter case, a root-squashing nfs server would
create the new file as user nobody, then refuse to allow fchown.
If VIR_FILE_CREATE_AS_UID is not specified, the simpler tactic of
creating the file/dir, then chowning is is used. This gives better
results in cases where the parent directory isn't on a root-squashing
NFS server, but doesn't give permission for the specified uid/gid to
create files. (Note that if the fork/setuid method fails to create the
file due to access privileges, the parent process will make a second
attempt using this simpler method.)
Return from both of these functions is 0 on success, or the value of
errno if there was a failure.
---
src/util/util.c | 247 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
src/util/util.h | 9 ++
2 files changed, 256 insertions(+), 0 deletions(-)
diff --git a/src/util/util.c b/src/util/util.c
index 1d493de..6d31f47 100644
--- a/src/util/util.c
+++ b/src/util/util.c
@@ -1126,6 +1126,253 @@ int virFileExists(const char *path)
return(0);
}
+
+static int virFileCreateSimple(const char *path, mode_t mode, uid_t uid, gid_t gid) {
+ int fd = -1;
+ int ret = 0;
+
+ if ((fd = open(path, O_RDWR | O_CREAT | O_EXCL, mode)) < 0) {
+ ret = errno;
+ virReportSystemError(NULL, errno, _("failed to create file %s"),
+ path);
+ goto error;
+ }
+ if ((getuid() == 0) && ((uid != 0) || (gid != 0))) {
+ if (fchown(fd, uid, gid) < 0) {
+ ret = errno;
+ virReportSystemError(NULL, errno, _("cannot chown %s to (%u, %u)"),
+ path, uid, gid);
+ close(fd);
+ goto error;
+ }
+ }
+ if (close(fd) < 0) {
+ ret = errno;
+ virReportSystemError(NULL, errno, _("failed to close new file %s"),
+ path);
+ goto error;
+ }
+ fd = -1;
+error:
+ return ret;
+}
+
+static int virDirCreateSimple(const char *path, mode_t mode, uid_t uid, gid_t gid) {
+ int ret = 0;
+
+ if (mkdir(path, mode) < 0) {
+ ret = errno;
+ virReportSystemError(NULL, errno, _("failed to create directory %s"),
+ path);
+ goto error;
+ }
+
+ if ((getuid() == 0) && ((uid != 0) || (gid != getgid()))) {
+ if (chown(path, uid, gid) < 0) {
+ ret = errno;
+ virReportSystemError(NULL, errno, _("cannot chown %s to (%u, %u)"),
+ path, uid, gid);
+ goto error;
+ }
+ }
+error:
+ return ret;
+}
+
+#ifndef WIN32
+int virFileCreate(const char *path, mode_t mode,
+ uid_t uid, gid_t gid, unsigned int flags) {
+ pid_t pid;
+ int waitret, status, ret = 0;
+ int fd = -1;
+
+ if ((!(flags & VIR_FILE_CREATE_AS_UID))
+ || (getuid() != 0)
+ || ((uid == 0) && (gid == 0))) {
+ return virFileCreateSimple(path, mode, uid, gid);
+ }
+
+ /* parent is running as root, but caller requested that the
+ * file be created as some other user and/or group). The
+ * following dance avoids problems caused by root-squashing
+ * NFS servers. */
+
+ if ((pid = fork()) < 0) {
+ ret = errno;
+ virReportSystemError(NULL, errno,
+ _("cannot fork o create file '%s'"), path);
+ return ret;
+ }
+
+ if (pid) { /* parent */
+ /* wait for child to complete, and retrieve its exit code */
+ while ((waitret = waitpid(pid, &status, 0) == -1)
+ && (errno == EINTR));
+ if (waitret == -1) {
+ ret = errno;
+ virReportSystemError(NULL, errno,
+ _("failed to wait for child creating '%s'"),
+ path);
+ return ret;
+ }
+ ret = WEXITSTATUS(status);
+ if (!WIFEXITED(status) || (ret == EACCES)) {
+ /* fall back to the simpler method, which works better in
+ * some cases */
+ /* Should we log a warning here? */
+ return virFileCreateSimple(path, mode, uid, gid);
+ }
+ if ((ret == 0) && (gid != 0)) {
+ /* check if group was set properly by creating after
+ * setgid. If not, try doing it with chown */
+ struct stat st;
+ if (stat(path, &st) == -1) {
+ ret = errno;
+ virReportSystemError(NULL, errno,
+ _("stat of '%s' failed"),
+ path);
+ return ret;
+ }
+ if ((st.st_gid != gid) && (chown(path, -1, gid) < 0)) {
+ ret = errno;
+ virReportSystemError(NULL, errno, _("cannot chown %s to group %u"),
+ path, gid);
+ }
+ }
+ return ret;
+ }
+
+ /* child - set desired uid/gid, then attempt to create the file */
+
+ if ((gid != 0) && (setgid(gid) != 0)) {
+ ret = errno;
+ virReportSystemError(NULL, errno, _("cannot set gid %u creating %s"),
+ gid, path);
+ goto childerror;
+ }
+ if ((uid != 0) && (setuid(uid) != 0)) {
+ ret = errno;
+ virReportSystemError(NULL, errno, _("cannot set uid %u creating %s"),
+ uid, path);
+ goto childerror;
+ }
+ if ((fd = open(path, O_RDWR | O_CREAT | O_EXCL, mode)) < 0) {
+ ret = errno;
+ if (ret != EACCES) {
+ /* in case of EACCES, the parent will retry */
+ virReportSystemError(NULL, errno, _("child failed to create file %s"),
+ path);
+ }
+ goto childerror;
+ }
+ if (close(fd) < 0) {
+ ret = errno;
+ virReportSystemError(NULL, errno, _("child failed to close new file %s"),
+ path);
+ goto childerror;
+ }
+childerror:
+ _exit(ret);
+
+}
+
+int virDirCreate(const char *path, mode_t mode,
+ uid_t uid, gid_t gid, unsigned int flags) {
+ pid_t pid;
+ int waitret;
+ int status, ret = 0;
+
+ if ((!(flags & VIR_FILE_CREATE_AS_UID))
+ || (getuid() != 0)
+ || ((uid == 0) && (gid == 0))) {
+ return virDirCreateSimple(path, mode, uid, gid);
+ }
+
+ if ((pid = fork()) < 0) {
+ ret = errno;
+ virReportSystemError(NULL, errno,
+ _("cannot fork to create directory '%s'"),
+ path);
+ return ret;
+ }
+
+ if (pid) { /* parent */
+ /* wait for child to complete, and retrieve its exit code */
+ while ((waitret = waitpid(pid, &status, 0) == -1) && (errno == EINTR));
+ if (waitret == -1) {
+ ret = errno;
+ virReportSystemError(NULL, errno,
+ _("failed to wait for child creating '%s'"),
+ path);
+ return ret;
+ }
+ ret = WEXITSTATUS(status);
+ if (!WIFEXITED(status) || (ret == EACCES)) {
+ /* fall back to the simpler method, which works better in some cases */
+ /* Should we log a warning here? */
+ return virDirCreateSimple(path, mode, uid, gid);
+ }
+ if ((ret == 0) && (gid != 0)) {
+ /* check if group was set properly by creating after
+ * setgid. If not, try doing it with chown */
+ struct stat st;
+ if (stat(path, &st) == -1) {
+ ret = errno;
+ virReportSystemError(NULL, errno,
+ _("stat of '%s' failed"),
+ path);
+ return ret;
+ }
+ if ((st.st_gid != gid) && (chown(path, -1, gid) < 0)) {
+ ret = errno;
+ virReportSystemError(NULL, errno, _("cannot chown %s to group %u"),
+ path, gid);
+ }
+ }
+
+ return ret;
+ }
+
+ /* child - set desired uid/gid, then attempt to create the directory */
+
+ if ((gid != 0) && (setgid(gid) != 0)) {
+ ret = errno;
+ virReportSystemError(NULL, errno, _("cannot set gid %u creating %s"),
+ gid, path);
+ goto childerror;
+ }
+ if ((uid != 0) && (setuid(uid) != 0)) {
+ ret = errno;
+ virReportSystemError(NULL, errno, _("cannot set uid %u creating %s"),
+ uid, path);
+ goto childerror;
+ }
+ if (mkdir(path, mode) < 0) {
+ ret = errno;
+ if (ret != EACCES) {
+ /* in case of EACCES, the parent will retry */
+ virReportSystemError(NULL, errno, _("child failed to create directory %s"),
+ path);
+ }
+ goto childerror;
+ }
+childerror:
+ _exit(ret);
+}
+
+#else /* WIN32 */
+
+int virFileCreate(const char *path, mode_t mode,
+ uid_t uid, gid_t gid, unsigned int flags) {
+ return virFileCreateSimple(path, mode, uid, gid);
+}
+
+int virDirCreate(const char *path, mode_t mode,
+ uid_t uid, gid_t gid, unsigned int flags) {
+ return virDirCreateSimple(path, mode, uid, gid);
+}
+#endif
+
int virFileMakePath(const char *path)
{
struct stat st;
diff --git a/src/util/util.h b/src/util/util.h
index 5e70038..2762862 100644
--- a/src/util/util.h
+++ b/src/util/util.h
@@ -111,6 +111,15 @@ char *virFindFileInPath(const char *file);
int virFileExists(const char *path);
+enum {
+ VIR_FILE_CREATE_NONE = 0,
+ VIR_FILE_CREATE_AS_UID = (1 << 0),
+};
+
+int virFileCreate(const char *path, mode_t mode, uid_t uid, gid_t gid,
+ unsigned int flags) ATTRIBUTE_RETURN_CHECK;
+int virDirCreate(const char *path, mode_t mode, uid_t uid, gid_t gid,
+ unsigned int flags) ATTRIBUTE_RETURN_CHECK;
int virFileMakePath(const char *path) ATTRIBUTE_RETURN_CHECK;
int virFileBuildPath(const char *dir,
--
1.6.6
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