[libvirt] [PATCH 3/7] util: make virSetUIDGID async-signal-safe
Eric Blake
eblake at redhat.com
Tue Jul 23 15:03:56 UTC 2013
https://bugzilla.redhat.com/show_bug.cgi?id=964358
POSIX states that multi-threaded apps should not use functions
that are not async-signal-safe between fork and exec, yet we
were using getpwuid_r and initgroups. Although rare, it is
possible to hit deadlock in the child, when it tries to grab
a mutex that was already held by another thread in the parent.
I actually hit this deadlock when testing multiple domains
being started in parallel with a command hook, with the following
backtrace in the child:
Thread 1 (Thread 0x7fd56bbf2700 (LWP 3212)):
#0 __lll_lock_wait ()
at ../nptl/sysdeps/unix/sysv/linux/x86_64/lowlevellock.S:136
#1 0x00007fd5761e7388 in _L_lock_854 () from /lib64/libpthread.so.0
#2 0x00007fd5761e7257 in __pthread_mutex_lock (mutex=0x7fd56be00360)
at pthread_mutex_lock.c:61
#3 0x00007fd56bbf9fc5 in _nss_files_getpwuid_r (uid=0, result=0x7fd56bbf0c70,
buffer=0x7fd55c2a65f0 "", buflen=1024, errnop=0x7fd56bbf25b8)
at nss_files/files-pwd.c:40
#4 0x00007fd575aeff1d in __getpwuid_r (uid=0, resbuf=0x7fd56bbf0c70,
buffer=0x7fd55c2a65f0 "", buflen=1024, result=0x7fd56bbf0cb0)
at ../nss/getXXbyYY_r.c:253
#5 0x00007fd578aebafc in virSetUIDGID (uid=0, gid=0) at util/virutil.c:1031
#6 0x00007fd578aebf43 in virSetUIDGIDWithCaps (uid=0, gid=0, capBits=0,
clearExistingCaps=true) at util/virutil.c:1388
#7 0x00007fd578a9a20b in virExec (cmd=0x7fd55c231f10) at util/vircommand.c:654
#8 0x00007fd578a9dfa2 in virCommandRunAsync (cmd=0x7fd55c231f10, pid=0x0)
at util/vircommand.c:2247
#9 0x00007fd578a9d74e in virCommandRun (cmd=0x7fd55c231f10, exitstatus=0x0)
at util/vircommand.c:2100
#10 0x00007fd56326fde5 in qemuProcessStart (conn=0x7fd53c000df0,
driver=0x7fd55c0dc4f0, vm=0x7fd54800b100, migrateFrom=0x0, stdin_fd=-1,
stdin_path=0x0, snapshot=0x0, vmop=VIR_NETDEV_VPORT_PROFILE_OP_CREATE,
flags=1) at qemu/qemu_process.c:3694
...
The solution is to split the work of getpwuid_r/initgroups into the
unsafe portions (getgrouplist, called pre-fork) and safe portions
(setgroups, called post-fork).
* src/util/virutil.h (virSetUIDGID, virSetUIDGIDWithCaps): Adjust
signature.
* src/util/virutil.c (virSetUIDGID): Add parameters.
(virSetUIDGIDWithCaps): Adjust clients.
* src/util/vircommand.c (virExec): Likewise.
* src/util/virfile.c (virFileAccessibleAs, virFileOpenForked)
(virDirCreate): Likewise.
* src/security/security_dac.c (virSecurityDACSetProcessLabel):
Likewise.
* src/lxc/lxc_container.c (lxcContainerSetID): Likewise.
* configure.ac (AC_CHECK_FUNCS_ONCE): Check for setgroups, not
initgroups.
Signed-off-by: Eric Blake <eblake at redhat.com>
(cherry picked from commit ee777e994927ed5f2d427fbc5a53cbe8b5969bda)
Conflicts:
src/lxc/lxc_container.c - did not use setUIDGID before 1.1.0
src/util/virutil.c - oom handling changes not backported; no virSetUIDGIDWithCaps
src/util/virfile.c - functions still lived in virutil.c this far back
configure.ac - context with previous commit
src/util/command.c - no UID/GID handling in vircommand.c...
src/storage/storage_backend.c - ...so do it in the one hook user instead
---
configure.ac | 4 +-
src/lxc/lxc_container.c | 2 +-
src/security/security_dac.c | 16 ++++--
src/storage/storage_backend.c | 16 +++++-
src/util/util.c | 129 +++++++++++++++++-------------------------
src/util/util.h | 2 +-
6 files changed, 83 insertions(+), 86 deletions(-)
diff --git a/configure.ac b/configure.ac
index aeff11d..ca34ac1 100644
--- a/configure.ac
+++ b/configure.ac
@@ -172,8 +172,8 @@ AC_CHECK_SIZEOF([long])
dnl Availability of various common functions (non-fatal if missing),
dnl and various less common threadsafe functions
AC_CHECK_FUNCS_ONCE([cfmakeraw geteuid getgid getgrnam_r getgrouplist getmntent_r \
- getpwuid_r getuid initgroups kill mmap newlocale posix_fallocate \
- posix_memalign regexec sched_getaffinity])
+ getpwuid_r getuid kill mmap newlocale posix_fallocate posix_memalign \
+ prlimit regexec sched_getaffinity setgroups])
dnl Availability of pthread functions (if missing, win32 threading is
dnl assumed). Because of $LIB_PTHREAD, we cannot use AC_CHECK_FUNCS_ONCE.
diff --git a/src/lxc/lxc_container.c b/src/lxc/lxc_container.c
index 8faa664..9d94042 100644
--- a/src/lxc/lxc_container.c
+++ b/src/lxc/lxc_container.c
@@ -1,5 +1,5 @@
/*
- * Copyright (C) 2008-2012 Red Hat, Inc.
+ * Copyright (C) 2008-2013 Red Hat, Inc.
* Copyright (C) 2008 IBM Corp.
*
* lxc_container.c: file description
diff --git a/src/security/security_dac.c b/src/security/security_dac.c
index ae5d8aa..61b705c 100644
--- a/src/security/security_dac.c
+++ b/src/security/security_dac.c
@@ -839,16 +839,24 @@ virSecurityDACSetProcessLabel(virSecurityManagerPtr mgr,
uid_t user;
gid_t group;
virSecurityDACDataPtr priv = virSecurityManagerGetPrivateData(mgr);
+ gid_t *groups;
+ int ngroups;
+ int ret = -1;
if (virSecurityDACGetIds(def, priv, &user, &group))
return -1;
+ ngroups = virGetGroupList(user, group, &groups);
+ if (ngroups < 0)
+ return -1;
VIR_DEBUG("Dropping privileges of DEF to %u:%u", user, group);
- if (virSetUIDGID(user, group) < 0)
- return -1;
-
- return 0;
+ if (virSetUIDGID(user, group, groups, ngroups) < 0)
+ goto cleanup;
+ ret = 0;
+cleanup:
+ VIR_FREE(groups);
+ return ret;
}
diff --git a/src/storage/storage_backend.c b/src/storage/storage_backend.c
index 75a3667..c820d74 100644
--- a/src/storage/storage_backend.c
+++ b/src/storage/storage_backend.c
@@ -538,6 +538,8 @@ cleanup:
struct hookdata {
virStorageVolDefPtr vol;
bool skip;
+ gid_t *groups;
+ int ngroups;
};
static int virStorageBuildSetUIDHook(void *data) {
@@ -547,9 +549,13 @@ static int virStorageBuildSetUIDHook(void *data) {
if (tmp->skip)
return 0;
- if (virSetUIDGID(vol->target.perms.uid, vol->target.perms.gid) < 0)
+ if (virSetUIDGID(vol->target.perms.uid, vol->target.perms.gid,
+ tmp->groups, tmp->ngroups) < 0) {
+ VIR_FREE(tmp->groups);
return -1;
+ }
+ VIR_FREE(tmp->groups);
return 0;
}
@@ -560,7 +566,7 @@ static int virStorageBackendCreateExecCommand(virStoragePoolObjPtr pool,
gid_t gid;
uid_t uid;
int filecreated = 0;
- struct hookdata data = {vol, false};
+ struct hookdata data = {vol, false, NULL, 0};
if ((pool->def->type == VIR_STORAGE_POOL_NETFS)
&& (((getuid() == 0)
@@ -569,6 +575,11 @@ static int virStorageBackendCreateExecCommand(virStoragePoolObjPtr pool,
|| ((vol->target.perms.gid != -1)
&& (vol->target.perms.gid != getgid())))) {
+ if ((data.ngroups = virGetGroupList(vol->target.perms.uid,
+ vol->target.perms.gid,
+ &data.groups)) < 0)
+ return -1;
+
virCommandSetPreExecHook(cmd, virStorageBuildSetUIDHook, &data);
if (virCommandRun(cmd, NULL) == 0) {
@@ -576,6 +587,7 @@ static int virStorageBackendCreateExecCommand(virStoragePoolObjPtr pool,
if (stat(vol->target.path, &st) >=0)
filecreated = 1;
}
+ VIR_FREE(data.groups);
}
data.skip = true;
diff --git a/src/util/util.c b/src/util/util.c
index 5ca5034..f0ccaf4 100644
--- a/src/util/util.c
+++ b/src/util/util.c
@@ -718,18 +718,26 @@ virFileAccessibleAs(const char *path, int mode,
pid_t pid = 0;
int status, ret = 0;
int forkRet = 0;
+ gid_t *groups;
+ int ngroups;
if (uid == getuid() &&
gid == getgid())
return access(path, mode);
+ ngroups = virGetGroupList(uid, gid, &groups);
+ if (ngroups < 0)
+ return -1;
+
forkRet = virFork(&pid);
if (pid < 0) {
+ VIR_FREE(groups);
return -1;
}
if (pid) { /* parent */
+ VIR_FREE(groups);
if (virProcessWait(pid, &status) < 0) {
/* virProcessWait() already
* reported error */
@@ -758,7 +766,7 @@ virFileAccessibleAs(const char *path, int mode,
goto childerror;
}
- if (virSetUIDGID(uid, gid) < 0) {
+ if (virSetUIDGID(uid, gid, groups, ngroups) < 0) {
ret = errno;
goto childerror;
}
@@ -834,17 +842,24 @@ virFileOpenForked(const char *path, int openflags, mode_t mode,
int fd = -1;
int pair[2] = { -1, -1 };
int forkRet;
+ gid_t *groups;
+ int ngroups;
/* parent is running as root, but caller requested that the
* file be opened as some other user and/or group). The
* following dance avoids problems caused by root-squashing
* NFS servers. */
+ ngroups = virGetGroupList(uid, gid, &groups);
+ if (ngroups < 0)
+ return -errno;
+
if (socketpair(AF_UNIX, SOCK_STREAM, 0, pair) < 0) {
ret = -errno;
virReportSystemError(errno,
_("failed to create socket needed for '%s'"),
path);
+ VIR_FREE(groups);
return ret;
}
@@ -865,7 +880,7 @@ virFileOpenForked(const char *path, int openflags, mode_t mode,
/* set desired uid/gid, then attempt to create the file */
- if (virSetUIDGID(uid, gid) < 0) {
+ if (virSetUIDGID(uid, gid, groups, ngroups) < 0) {
ret = -errno;
goto childerror;
}
@@ -913,6 +928,7 @@ virFileOpenForked(const char *path, int openflags, mode_t mode,
/* parent */
+ VIR_FREE(groups);
VIR_FORCE_CLOSE(pair[1]);
do {
@@ -1123,6 +1139,8 @@ int virDirCreate(const char *path, mode_t mode,
pid_t pid;
int waitret;
int status, ret = 0;
+ gid_t *groups;
+ int ngroups;
/* allow using -1 to mean "current value" */
if (uid == (uid_t) -1)
@@ -1137,15 +1155,21 @@ int virDirCreate(const char *path, mode_t mode,
return virDirCreateNoFork(path, mode, uid, gid, flags);
}
+ ngroups = virGetGroupList(uid, gid, &groups);
+ if (ngroups < 0)
+ return -errno;
+
int forkRet = virFork(&pid);
if (pid < 0) {
ret = -errno;
+ VIR_FREE(groups);
return ret;
}
if (pid) { /* parent */
/* wait for child to complete, and retrieve its exit code */
+ VIR_FREE(groups);
while ((waitret = waitpid(pid, &status, 0) == -1) && (errno == EINTR));
if (waitret == -1) {
ret = -errno;
@@ -1172,7 +1196,7 @@ parenterror:
/* set desired uid/gid, then attempt to create the directory */
- if (virSetUIDGID(uid, gid) < 0) {
+ if (virSetUIDGID(uid, gid, groups, ngroups) < 0) {
ret = -errno;
goto childerror;
}
@@ -2635,87 +2659,38 @@ no_memory:
goto cleanup;
}
-/* Set the real and effective uid and gid to the given values, and call
- * initgroups so that the process has all the assumed group membership of
- * that uid. return 0 on success, -1 on failure (the original system error
- * remains in errno).
+/* Set the real and effective uid and gid to the given values, as well
+ * as all the supplementary groups, so that the process has all the
+ * assumed group membership of that uid. Return 0 on success, -1 on
+ * failure (the original system error remains in errno).
*/
int
-virSetUIDGID(uid_t uid, gid_t gid)
+virSetUIDGID(uid_t uid, gid_t gid, gid_t *groups ATTRIBUTE_UNUSED,
+ int ngroups ATTRIBUTE_UNUSED)
{
- int err;
- char *buf = NULL;
-
- if (gid > 0) {
- if (setregid(gid, gid) < 0) {
- virReportSystemError(err = errno,
- _("cannot change to '%d' group"),
- (unsigned int) gid);
- goto error;
- }
+ if (gid != (gid_t)-1 && setregid(gid, gid) < 0) {
+ virReportSystemError(errno,
+ _("cannot change to '%u' group"),
+ (unsigned int) gid);
+ return -1;
}
- if (uid > 0) {
-# ifdef HAVE_INITGROUPS
- struct passwd pwd, *pwd_result;
- size_t bufsize;
- int rc;
-
- bufsize = sysconf(_SC_GETPW_R_SIZE_MAX);
- if (bufsize == -1)
- bufsize = 16384;
-
- if (VIR_ALLOC_N(buf, bufsize) < 0) {
- virReportOOMError();
- err = ENOMEM;
- goto error;
- }
- while ((rc = getpwuid_r(uid, &pwd, buf, bufsize,
- &pwd_result)) == ERANGE) {
- if (VIR_RESIZE_N(buf, bufsize, bufsize, bufsize) < 0) {
- virReportOOMError();
- err = ENOMEM;
- goto error;
- }
- }
-
- if (rc) {
- virReportSystemError(err = rc, _("cannot getpwuid_r(%d)"),
- (unsigned int) uid);
- goto error;
- }
-
- if (!pwd_result) {
- virReportError(VIR_ERR_INTERNAL_ERROR,
- _("getpwuid_r failed to retrieve data "
- "for uid '%d'"),
- (unsigned int) uid);
- err = EINVAL;
- goto error;
- }
-
- if (initgroups(pwd.pw_name, pwd.pw_gid) < 0) {
- virReportSystemError(err = errno,
- _("cannot initgroups(\"%s\", %d)"),
- pwd.pw_name, (unsigned int) pwd.pw_gid);
- goto error;
- }
+# if HAVE_SETGROUPS
+ if (ngroups && setgroups(ngroups, groups) < 0) {
+ virReportSystemError(errno, "%s",
+ _("cannot set supplemental groups"));
+ return -1;
+ }
# endif
- if (setreuid(uid, uid) < 0) {
- virReportSystemError(err = errno,
- _("cannot change to uid to '%d'"),
- (unsigned int) uid);
- goto error;
- }
+
+ if (uid != (uid_t)-1 && setreuid(uid, uid) < 0) {
+ virReportSystemError(errno,
+ _("cannot change to uid to '%u'"),
+ (unsigned int) uid);
+ return -1;
}
- VIR_FREE(buf);
return 0;
-
-error:
- VIR_FREE(buf);
- errno = err;
- return -1;
}
#else /* ! HAVE_GETPWUID_R */
@@ -2932,7 +2907,9 @@ int virGetGroupID(const char *name ATTRIBUTE_UNUSED,
int
virSetUIDGID(uid_t uid ATTRIBUTE_UNUSED,
- gid_t gid ATTRIBUTE_UNUSED)
+ gid_t gid ATTRIBUTE_UNUSED,
+ gid_t *groups ATTRIBUTE_UNUSED,
+ int ngroups ATTRIBUTE_UNUSED)
{
virReportError(VIR_ERR_INTERNAL_ERROR,
"%s", _("virSetUIDGID is not available"));
diff --git a/src/util/util.h b/src/util/util.h
index 98964b2..0f904c3 100644
--- a/src/util/util.h
+++ b/src/util/util.h
@@ -53,7 +53,7 @@ int virSetCloseExec(int fd) ATTRIBUTE_RETURN_CHECK;
int virPipeReadUntilEOF(int outfd, int errfd,
char **outbuf, char **errbuf);
-int virSetUIDGID(uid_t uid, gid_t gid);
+int virSetUIDGID(uid_t uid, gid_t gid, gid_t *groups, int ngroups);
int virFileReadLimFD(int fd, int maxlen, char **buf) ATTRIBUTE_RETURN_CHECK;
--
1.8.3.1
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