Ignore EPERM for root when setting IMA signature xattr

This lets installations succeed even if the ima plugin happens to be
installed in a rootless container, where IMA isn't supported. We can't
specifically test for rootless container, but I don't know what other
situation would result in EPERM for root when setting IMA so it seems
like a reasonable heuristic for this.

Testing this is a bit tricky: we expect the install to succeed in all cases,
but whether IMA actually gets set depends on the container.

Fixes: #3234

plugins/ima.c

@@ -71,7 +71,9 @@ static rpmRC ima_fsm_file_prepare(rpmPlugin plugin, rpmfi fi, int fd,
 	    else
 		xx = lsetxattr(path, XATTR_NAME_IMA, fsig, len, 0);
 	    if (xx < 0) {
-		int is_err = errno != EOPNOTSUPP;
+		/* unsupported fs or root inside rootless container? */
+		int is_err = !(errno == EOPNOTSUPP ||
+			      (errno == EPERM && getuid() == 0));
 
 	        rpmlog(is_err?RPMLOG_ERR:RPMLOG_DEBUG,
 			"ima: could not apply signature on '%s': %s\n",

tests/rpmsigdig.at

@@ -1891,6 +1891,36 @@ hello-1.0.tar.gz:(none)
 [])
 RPMTEST_CLEANUP
 
+# Test that installing an ima signed package works.
+# The installation should succeed in all cases, but whether setting the
+# IMA signature succeeds depends on container privileges - in rootless
+# we can't do this.
+AT_SETUP([install ima file signatures])
+AT_KEYWORDS([install ima signature])
+AT_SKIP_IF([$IMA_DISABLED])
+
+RPMTEST_SETUP
+
+cat << EOF > expout
+# file: /usr/share/example1
+security.ima=0sAwIEpZglVABIMEYCIQDlEXva+nO6rrHx3EbsqkaYGmLUF3RaM1MlcrY9xtldFgIhAMeJEHrFuR4tkV4d88e3hBT2s/UImdRMHeOB0Ok438gr
+
+EOF
+
+touch canary
+# different expectations in a rootless container
+if ! setfattr -n security.ima -v 0sAwIEpZglVABIMEYCIQDlEXva+nO6rrHx3EbsqkaYGmLUF3RaM1MlcrY9xtldFgIhAMeJEHrFuR4tkV4d88e3hBT2s/UImdRMHeOB0Ok438gr canary 2> /dev/null; then
+    echo -n "" > expout
+fi
+
+RPMTEST_CHECK([
+runroot rpm -U /data/RPMS/imatest-1.0-1.fc34.noarch.rpm
+runroot_other getfattr --absolute-names -d -m security.ima /usr/share/example1
+],
+[0],
+[expout],
+[])
+RPMTEST_CLEANUP
 
 AT_SETUP([--delsign with misplaced ima signature])
 AT_KEYWORDS([rpmsign ima signature])