Re: [libvirt] [PATCH 2/2] util: make virSetUIDGID async-signal-safe

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. * configure.ac (AC_CHECK_FUNCS_ONCE): Check for setgroups, not initgroups. Signed-off-by: Eric Blake <eblake(a)redhat.com&gt; --- configure.ac | 5 +- src/security/security_dac.c | 16 +++++-- src/util/vircommand.c | 10 +++- src/util/virfile.c | 30 ++++++++++-- src/util/virutil.c | 108 ++++++++++++-------------------------------- src/util/virutil.h | 5 +- 6 files changed, 84 insertions(+), 90 deletions(-) diff --git a/configure.ac b/configure.ac index d20b90e..26deac7 100644 --- a/configure.ac +++ b/configure.ac @@ -206,8 +206,9 @@ 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 prlimit regexec sched_getaffinity setns setrlimit symlink]) + getmntent_r getpwuid_r getuid kill mmap newlocale posix_fallocate \ + posix_memalign prlimit regexec sched_getaffinity setgroups setns \ + setrlimit symlink]) 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/security/security_dac.c b/src/security/security_dac.c index d922ad2..907dbd5 100644 --- a/src/security/security_dac.c +++ b/src/security/security_dac.c @@ -1000,17 +1000,25 @@ 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", (unsigned int) user, (unsigned int) 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/util/vircommand.c b/src/util/vircommand.c index 665f549..ba03802 100644 --- a/src/util/vircommand.c +++ b/src/util/vircommand.c @@ -402,6 +402,8 @@ virExec(virCommandPtr cmd) const char *binary = NULL; int forkRet, ret; struct sigaction waxon, waxoff; + gid_t *groups = NULL; + int ngroups; if (cmd->args[0][0] != '/') { if (!(binary = virFindFileInPath(cmd->args[0]))) { @@ -472,6 +474,9 @@ virExec(virCommandPtr cmd) childerr = null; } + if ((ngroups = virGetGroupList(cmd->uid, cmd->gid, &groups)) < 0) + goto cleanup; + forkRet = virFork(&pid); if (pid < 0) { @@ -497,6 +502,7 @@ virExec(virCommandPtr cmd) if (binary != cmd->args[0]) VIR_FREE(binary); + VIR_FREE(groups); return 0; } @@ -651,7 +657,8 @@ virExec(virCommandPtr cmd) cmd->capabilities || (cmd->flags & VIR_EXEC_CLEAR_CAPS)) { VIR_DEBUG("Setting child uid:gid to %d:%d with caps %llx", (int)cmd->uid, (int)cmd->gid, cmd->capabilities); - if (virSetUIDGIDWithCaps(cmd->uid, cmd->gid, cmd->capabilities, + if (virSetUIDGIDWithCaps(cmd->uid, cmd->gid, groups, ngroups, + cmd->capabilities, !!(cmd->flags & VIR_EXEC_CLEAR_CAPS)) < 0) { goto fork_error; } @@ -695,6 +702,7 @@ virExec(virCommandPtr cmd) /* This is cleanup of parent process only - child should never jump here on error */ + VIR_FREE(groups); if (binary != cmd->args[0]) VIR_FREE(binary); diff --git a/src/util/virfile.c b/src/util/virfile.c index 4637919..20ebcbc 100644 --- a/src/util/virfile.c +++ b/src/util/virfile.c @@ -1462,18 +1462,26 @@ 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 */ @@ -1502,7 +1510,7 @@ virFileAccessibleAs(const char *path, int mode, goto childerror; } - if (virSetUIDGID(uid, gid) < 0) { + if (virSetUIDGID(uid, gid, groups, ngroups) < 0) { ret = errno; goto childerror; } @@ -1578,17 +1586,24 @@ 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; } @@ -1609,7 +1624,7 @@ 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; } @@ -1657,6 +1672,7 @@ virFileOpenForked(const char *path, int openflags, mode_t mode, /* parent */ + VIR_FREE(groups); VIR_FORCE_CLOSE(pair[1]); do { @@ -1858,6 +1874,8 @@ virDirCreate(const char *path, 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) @@ -1872,15 +1890,21 @@ virDirCreate(const char *path, 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; @@ -1907,7 +1931,7 @@ 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; } diff --git a/src/util/virutil.c b/src/util/virutil.c index a3cb64f..883672a 100644 --- a/src/util/virutil.c +++ b/src/util/virutil.c @@ -1086,87 +1086,37 @@ error: } -/* 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, int ngroups) { - int err; - char *buf = NULL; - - if (gid != (gid_t)-1) { - if (setregid(gid, gid) < 0) { - virReportSystemError(err = errno, - _("cannot change to '%u' 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 != (uid_t)-1) { -# 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(%u)"), - (unsigned int) uid); - goto error; - } - - if (!pwd_result) { - virReportError(VIR_ERR_INTERNAL_ERROR, - _("getpwuid_r failed to retrieve data " - "for uid '%u'"), - (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 '%u'"), - (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 */ @@ -1383,7 +1333,9 @@ 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")); @@ -1407,8 +1359,8 @@ virGetGroupName(gid_t gid ATTRIBUTE_UNUSED) * errno). */ int -virSetUIDGIDWithCaps(uid_t uid, gid_t gid, unsigned long long capBits, - bool clearExistingCaps) +virSetUIDGIDWithCaps(uid_t uid, gid_t gid, gid_t *groups, int ngroups, + unsigned long long capBits, bool clearExistingCaps) { int ii, capng_ret, ret = -1; bool need_setgid = false, need_setuid = false; @@ -1478,7 +1430,7 @@ virSetUIDGIDWithCaps(uid_t uid, gid_t gid, unsigned long long capBits, } } - if (virSetUIDGID(uid, gid) < 0) + if (virSetUIDGID(uid, gid, groups, ngroups) < 0) goto cleanup; /* Tell it we are done keeping capabilities */ @@ -1522,11 +1474,11 @@ cleanup: */ int -virSetUIDGIDWithCaps(uid_t uid, gid_t gid, +virSetUIDGIDWithCaps(uid_t uid, gid_t gid, gid_t *groups, int ngroups, unsigned long long capBits ATTRIBUTE_UNUSED, bool clearExistingCaps ATTRIBUTE_UNUSED) { - return virSetUIDGID(uid, gid); + return virSetUIDGID(uid, gid, groups, ngroups); } #endif diff --git a/src/util/virutil.h b/src/util/virutil.h index 6480b07..0083c88 100644 --- a/src/util/virutil.h +++ b/src/util/virutil.h @@ -46,8 +46,9 @@ 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 virSetUIDGIDWithCaps(uid_t uid, gid_t gid, unsigned long long capBits, +int virSetUIDGID(uid_t uid, gid_t gid, gid_t *groups, int ngroups); +int virSetUIDGIDWithCaps(uid_t uid, gid_t gid, gid_t *groups, int ngroups, + unsigned long long capBits, bool clearExistingCaps); int virScaleInteger(unsigned long long *value, const char *suffix,