plugins/fsverity: Install fsverity signatures

This plugin installs fsverity signatures for regular files, when a signature
is found in the RPM. It tries to enable them unconditionally, but fails
gracefully if fsverity isn't supported or enabled.

Signed-off-by: Jes Sorensen <jsorensen@fb.com>

configure.ac

@@ -839,6 +839,11 @@ AS_IF([test "$enable_plugins" != no],[
 ])
 AM_CONDITIONAL(IMA, [test "x$ac_cv_func_lsetxattr" = xyes])
 
+AS_IF([test "$enable_plugins" != no],[
+AC_CHECK_HEADERS([linux/fsverity.h],[FSVERITY_IOCTL="yes"])
+])
+AM_CONDITIONAL(FSVERITY_IOCTL,[test "x$FSVERITY_IOCTL" = xyes])
+
 #=================
 # Check for audit library.
 AC_ARG_WITH(audit,

macros.in

@@ -734,6 +734,9 @@ package or when debugging this package.\
 # a wrong or missing signature.
 #%_ima_sign_config_files	0
 
+# Set to 1 to have fsverity signatures written for %config files.
+#%_fsverity_sign_config_files	0
+
 #
 # Default output format string for rpm -qa
 #
@@ -1173,6 +1176,7 @@ package or when debugging this package.\
 %__transaction_selinux		%{__plugindir}/selinux.so
 %__transaction_syslog		%{__plugindir}/syslog.so
 %__transaction_ima		%{__plugindir}/ima.so
+%__transaction_fsverity		%{__plugindir}/fsverity.so
 %__transaction_prioreset	%{__plugindir}/prioreset.so
 %__transaction_audit		%{__plugindir}/audit.so
 

plugins/Makefile.am

@@ -43,6 +43,12 @@ ima_la_LIBADD = $(top_builddir)/lib/librpm.la $(top_builddir)/rpmio/librpmio.la
 plugins_LTLIBRARIES += ima.la
 endif
 
+if FSVERITY_IOCTL
+fsverity_la_sources = fsverity.c
+fsverity_la_LIBADD = $(top_builddir)/lib/librpm.la $(top_builddir)/rpmio/librpmio.la
+plugins_LTLIBRARIES += fsverity.la
+endif
+
 if AUDIT
 audit_la_sources = audit.c
 audit_la_LIBADD = $(top_builddir)/lib/librpm.la $(top_builddir)/rpmio/librpmio.la @WITH_AUDIT_LIB@

plugins/fsverity.c

@@ -0,0 +1,177 @@
+/**
+ * Copyright (C) 2020 Facebook
+ *
+ * Author: Jes Sorensen <jsorensen@fb.com>
+ */
+
+#include "system.h"
+
+#include <errno.h>
+#include <fcntl.h>
+#include <sys/ioctl.h>
+#include <linux/fsverity.h>
+
+#include <rpm/rpmfi.h>
+#include <rpm/rpmte.h>
+#include <rpm/rpmfiles.h>
+#include <rpm/rpmtypes.h>
+#include <rpm/rpmlog.h>
+#include <rpmio/rpmstring.h>
+#include <rpmio/rpmmacro.h>
+
+#include "lib/rpmfs.h"
+#include "lib/rpmplugin.h"
+#include "lib/rpmte_internal.h"
+
+#include "sign/rpmsignverity.h"
+
+static int sign_config_files = 0;
+
+/*
+ * This unconditionally tries to apply the fsverity signature to a file,
+ * but fails gracefully if the file system doesn't support it or the
+ * verity feature flag isn't enabled in the file system (ext4).
+ */
+static rpmRC fsverity_fsm_file_prepare(rpmPlugin plugin, rpmfi fi,
+				       const char *path, const char *dest,
+				       mode_t file_mode, rpmFsmOp op)
+{
+    struct fsverity_enable_arg arg;
+    const unsigned char * signature = NULL;
+    size_t len;
+    int rc = RPMRC_OK;
+    int fd;
+    rpmFileAction action = XFO_ACTION(op);
+    char *buffer;
+
+    /* Ignore skipped files and unowned directories */
+    if (XFA_SKIPPING(action) || (op & FAF_UNOWNED)) {
+	rpmlog(RPMLOG_DEBUG, "fsverity skipping early: path %s dest %s\n",
+	       path, dest);
+	goto exit;
+    }
+
+    /*
+     * Do not install signatures for config files unless the
+     * user explicitly asks for it.
+     */
+    if (rpmfiFFlags(fi) & RPMFILE_CONFIG) {
+	if (!(rpmfiFMode(fi) & (S_IXUSR|S_IXGRP|S_IXOTH)) &&
+	    !sign_config_files) {
+	    rpmlog(RPMLOG_DEBUG, "fsverity skipping: path %s dest %s\n",
+		   path, dest);
+
+	    goto exit;
+	}
+    }
+
+    /*
+     * Right now fsverity doesn't deal with symlinks or directories, so do
+     * not try to install signatures for non regular files.
+     */
+    if (!S_ISREG(rpmfiFMode(fi))) {
+	rpmlog(RPMLOG_DEBUG, "fsverity skipping non regular: path %s dest %s\n",
+	       path, dest);
+	goto exit;
+    }
+
+    signature = rpmfiVSignature(fi, &len);
+    if (!signature || !len) {
+	rpmlog(RPMLOG_DEBUG, "fsverity no signature for: path %s dest %s\n",
+	       path, dest);
+	goto exit;
+    }
+
+    memset(&arg, 0, sizeof(arg));
+    arg.version = 1;
+    arg.hash_algorithm = FS_VERITY_HASH_ALG_SHA256;
+    arg.block_size = RPM_FSVERITY_BLKSZ;
+    arg.sig_ptr = (uintptr_t)signature;
+    arg.sig_size = len;
+
+    buffer = pgpHexStr(signature, arg.sig_size);
+    rpmlog(RPMLOG_DEBUG, "applying signature: %s\n", buffer);
+    free(buffer);
+
+    fd = open(path, O_RDONLY);
+    if (fd < 0) {
+	rpmlog(RPMLOG_ERR, "failed to open path %s\n", path);
+	goto exit;
+    }
+
+    /*
+     * Enable fsverity on the file.
+     * fsverity not supported by file system (ENOTTY) and fsverity not
+     * enabled on file system are expected and not considered
+     * errors. Every other non-zero error code will result in the
+     * installation failing.
+     */
+    if (ioctl(fd, FS_IOC_ENABLE_VERITY, &arg) != 0) {
+	switch(errno) {
+	case EBADMSG:
+	    rpmlog(RPMLOG_DEBUG, "invalid or malformed fsverity signature for %s\n", path);
+	    rc = RPMRC_FAIL;
+	    break;
+	case EEXIST:
+	    rpmlog(RPMLOG_DEBUG, "fsverity signature already enabled %s\n",
+		   path);
+	    rc = RPMRC_FAIL;
+	    break;
+	case EINVAL:
+	    rpmlog(RPMLOG_DEBUG, "invalid arguments for ioctl %s\n", path);
+	    rc = RPMRC_FAIL;
+	    break;
+	case EKEYREJECTED:
+	    rpmlog(RPMLOG_DEBUG, "signature doesn't match file %s\n", path);
+	    rc = RPMRC_FAIL;
+	    break;
+	case EMSGSIZE:
+	    rpmlog(RPMLOG_DEBUG, "invalid signature size for %s\n", path);
+	    rc = RPMRC_FAIL;
+	    break;
+	case ENOPKG:
+	    rpmlog(RPMLOG_DEBUG, "unsupported signature algoritm (%i) for %s\n",
+		   arg.hash_algorithm, path);
+	    rc = RPMRC_FAIL;
+	    break;
+	case ETXTBSY:
+	    rpmlog(RPMLOG_DEBUG, "file is open by other process %s\n",
+		   path);
+	    rc = RPMRC_FAIL;
+	    break;
+	case ENOTTY:
+	    rpmlog(RPMLOG_DEBUG, "fsverity not supported by file system for %s\n",
+		   path);
+	    break;
+	case EOPNOTSUPP:
+	    rpmlog(RPMLOG_DEBUG, "fsverity not enabled on file system for %s\n",
+		   path);
+	    break;
+	default:
+	    rpmlog(RPMLOG_DEBUG, "failed to enable verity (errno %i) for %s\n",
+		   errno, path);
+	    rc = RPMRC_FAIL;
+	    break;
+	}
+    }
+
+    rpmlog(RPMLOG_DEBUG, "fsverity enabled signature for: path %s dest %s\n",
+	   path, dest);
+    close(fd);
+exit:
+    return rc;
+}
+
+static rpmRC fsverity_init(rpmPlugin plugin, rpmts ts)
+{
+    sign_config_files = rpmExpandNumeric("%{?_fsverity_sign_config_files}");
+
+    rpmlog(RPMLOG_DEBUG, "fsverity_init\n");
+
+    return RPMRC_OK;
+}
+
+struct rpmPluginHooks_s fsverity_hooks = {
+    .init = fsverity_init,
+    .fsm_file_prepare = fsverity_fsm_file_prepare,
+};