[PATCH] Before clearing the capability bounding set, check if we have the cap

[harald@redhat.com]

From: Harald Hoyer <harald@redhat.com>

PR_CAPBSET_DROP can return EINVAL, if an older kernel does support
some capabilities, which are defined by CAP_LAST_CAP, which results in
a failure of the service.

For example kernel 3.4 errors on CAP_EPOLLWAKEUP, which was newly
introduced in 3.5.

So, for future capabilities, we clear until we get an EINVAL for
PR_CAPBSET_READ.
---
 support/nsm/file.c      |    2 +-
 utils/nfsdcld/nfsdcld.c |    4 ++--
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/support/nsm/file.c b/support/nsm/file.c
index 5476446..4711c2c 100644
--- a/support/nsm/file.c
+++ b/support/nsm/file.c
@@ -386,7 +386,7 @@ prune_bounding_set(void)
 	}
 
 	/* prune the bounding set to nothing */
-	for (i = 0; i <= CAP_LAST_CAP; ++i) {
+	for (i = 0; prctl(PR_CAPBSET_READ, i, 0, 0, 0) >=0 ; ++i) {
 		ret = prctl(PR_CAPBSET_DROP, i, 0, 0, 0);
 		if (ret) {
 			xlog(L_ERROR, "Unable to prune capability %lu from "
diff --git a/utils/nfsdcld/nfsdcld.c b/utils/nfsdcld/nfsdcld.c
index e7af4e3..473d069 100644
--- a/utils/nfsdcld/nfsdcld.c
+++ b/utils/nfsdcld/nfsdcld.c
@@ -102,8 +102,8 @@ cld_set_caps(void)
 	}
 
 	/* prune the bounding set to nothing */
-	for (i = 0; i <= CAP_LAST_CAP; ++i) {
-		ret = prctl(PR_CAPBSET_DROP, i);
+	for (i = 0; prctl(PR_CAPBSET_READ, i, 0, 0, 0) >= 0 ; ++i) {
+		ret = prctl(PR_CAPBSET_DROP, i, 0, 0, 0);
 		if (ret) {
 			xlog(L_ERROR, "Unable to prune capability %lu from "
 				      "bounding set: %m", i);
-- 
1.7.10.2