From 623a550b16835685ddca3736a9a00218bd582a2f Mon Sep 17 00:00:00 2001 From: Jeff Layton Date: Wed, 9 May 2012 13:25:34 -0400 Subject: [PATCH] nfsdcld: add support for dropping capabilities As a long running daemon, we need to be security-conscious with nfsdcld, so let's prune what it can do down to nearly nothing. We want the daemon to run as root so that it has access to open and reopen the rpc_pipefs pipe, but we don't actually need any of the superuser caps that come with it. Have it drop all capabilities early on. We don't need any of them as long as the fsuid continues to be 0. Once we do that though, check to ensure that the db dir is actually usable by root w/o CAP_DAC_OVERRIDE. Do an access() check on it and throw a warning if it's not. Hopefully that will assist users in debugging if they get the ownership of the DB dir wrong. Signed-off-by: Jeff Layton Signed-off-by: Steve Dickson --- utils/nfsdcld/Makefile.am | 2 +- utils/nfsdcld/nfsdcld.c | 82 ++++++++++++++++++++++++++++++++++++++- utils/nfsdcld/nfsdcld.man | 7 +++- utils/nfsdcld/sqlite.c | 6 +-- 4 files changed, 89 insertions(+), 8 deletions(-) diff --git a/utils/nfsdcld/Makefile.am b/utils/nfsdcld/Makefile.am index f320dff..073a71b 100644 --- a/utils/nfsdcld/Makefile.am +++ b/utils/nfsdcld/Makefile.am @@ -8,7 +8,7 @@ sbin_PROGRAMS = nfsdcld nfsdcld_SOURCES = nfsdcld.c sqlite.c -nfsdcld_LDADD = ../../support/nfs/libnfs.a $(LIBEVENT) $(LIBSQLITE) +nfsdcld_LDADD = ../../support/nfs/libnfs.a $(LIBEVENT) $(LIBSQLITE) $(LIBCAP) MAINTAINERCLEANFILES = Makefile.in diff --git a/utils/nfsdcld/nfsdcld.c b/utils/nfsdcld/nfsdcld.c index c9f0fb9..e7af4e3 100644 --- a/utils/nfsdcld/nfsdcld.c +++ b/utils/nfsdcld/nfsdcld.c @@ -34,6 +34,10 @@ #include #include #include +#ifdef HAVE_SYS_CAPABILITY_H +#include +#include +#endif #include "xlog.h" #include "nfslib.h" @@ -46,6 +50,10 @@ #define DEFAULT_CLD_PATH PIPEFS_DIR "/nfsd/cld" +#ifndef CLD_DEFAULT_STORAGEDIR +#define CLD_DEFAULT_STORAGEDIR NFS_STATEDIR "/nfsdcld" +#endif + #define UPCALL_VERSION 1 /* private data structures */ @@ -79,6 +87,47 @@ usage(char *progname) printf("%s [ -hFd ] [ -p pipe ] [ -s dir ]\n", progname); } +static int +cld_set_caps(void) +{ + int ret = 0; +#ifdef HAVE_SYS_CAPABILITY_H + unsigned long i; + cap_t caps; + + if (getuid() != 0) { + xlog(L_ERROR, "Not running as root. Daemon won't be able to " + "open the pipe after dropping capabilities!"); + return -EINVAL; + } + + /* prune the bounding set to nothing */ + for (i = 0; i <= CAP_LAST_CAP; ++i) { + ret = prctl(PR_CAPBSET_DROP, i); + if (ret) { + xlog(L_ERROR, "Unable to prune capability %lu from " + "bounding set: %m", i); + return -errno; + } + } + + /* get a blank capset */ + caps = cap_init(); + if (caps == NULL) { + xlog(L_ERROR, "Unable to get blank capability set: %m"); + return -errno; + } + + /* reset the process capabilities */ + if (cap_set_proc(caps) != 0) { + xlog(L_ERROR, "Unable to set process capabilities: %m"); + ret = -errno; + } + cap_free(caps); +#endif + return ret; +} + #define INOTIFY_EVENT_MAX (sizeof(struct inotify_event) + NAME_MAX) static int @@ -453,7 +502,7 @@ main(int argc, char **argv) int rc = 0; bool foreground = false; char *progname; - char *storagedir = NULL; + char *storagedir = CLD_DEFAULT_STORAGEDIR; struct cld_client clnt; memset(&clnt, 0, sizeof(clnt)); @@ -502,6 +551,37 @@ main(int argc, char **argv) } } + /* drop all capabilities */ + rc = cld_set_caps(); + if (rc) + goto out; + + /* + * now see if the storagedir is writable by root w/o CAP_DAC_OVERRIDE. + * If it isn't then give the user a warning but proceed as if + * everything is OK. If the DB has already been created, then + * everything might still work. If it doesn't exist at all, then + * assume that the maindb init will be able to create it. Fail on + * anything else. + */ + if (access(storagedir, W_OK) == -1) { + switch (errno) { + case EACCES: + xlog(L_WARNING, "Storage directory %s is not writable. " + "Should be owned by root and writable " + "by owner!", storagedir); + break; + case ENOENT: + /* ignore and assume that we can create dir as root */ + break; + default: + xlog(L_ERROR, "Unexpected error when checking access " + "on %s: %m", storagedir); + rc = -errno; + goto out; + } + } + /* set up storage db */ rc = sqlite_maindb_init(storagedir); if (rc) { diff --git a/utils/nfsdcld/nfsdcld.man b/utils/nfsdcld/nfsdcld.man index bad5f34..9ddaf64 100644 --- a/utils/nfsdcld/nfsdcld.man +++ b/utils/nfsdcld/nfsdcld.man @@ -160,7 +160,7 @@ Runs the daemon in the foreground and prints all output to stderr Location of the \*(L"cld\*(R" upcall pipe. The default value is \&\fI/var/lib/nfs/rpc_pipefs/nfsd/cld\fR. If the pipe does not exist when the daemon starts then it will wait for it to be created. -.IP "\fB\-s\fR \fIstoragedir\fR, \fB\-\-storagedir\fR=\fIstorage_dir\fR" 4 +.IP "\fB\-s\fR \fIstorage_dir\fR, \fB\-\-storagedir\fR=\fIstorage_dir\fR" 4 .IX Item "-s storagedir, --storagedir=storage_dir" Directory where stable storage information should be kept. The default value is \fI/var/lib/nfs/nfsdcld\fR. @@ -175,6 +175,11 @@ This daemon requires a kernel that supports the nfsdcld upcall. If the kernel does not support the new upcall, or is using the legacy client name tracking code then it will not create the pipe that nfsdcld uses to talk to the kernel. +.PP +This daemon should be run as root, as the pipe that it uses to communicate +with the kernel is only accessable by root. The daemon however does drop all +superuser capabilities after starting. Because of this, the \fIstoragedir\fR +should be owned by root, and be readable and writable by owner. .SH "AUTHORS" .IX Header "AUTHORS" The nfsdcld daemon was developed by Jeff Layton . diff --git a/utils/nfsdcld/sqlite.c b/utils/nfsdcld/sqlite.c index 9e35774..bb2519d 100644 --- a/utils/nfsdcld/sqlite.c +++ b/utils/nfsdcld/sqlite.c @@ -54,10 +54,6 @@ #define CLD_SQLITE_SCHEMA_VERSION 1 -#ifndef CLD_SQLITE_TOPDIR -#define CLD_SQLITE_TOPDIR NFS_STATEDIR "/nfsdcld" -#endif - /* in milliseconds */ #define CLD_SQLITE_BUSY_TIMEOUT 10000 @@ -112,7 +108,7 @@ sqlite_maindb_init(char *topdir) char *err = NULL; sqlite3_stmt *stmt = NULL; - sqlite_topdir = topdir ? topdir : CLD_SQLITE_TOPDIR; + sqlite_topdir = topdir; ret = mkdir_if_not_exist(sqlite_topdir); if (ret) -- 2.39.2