[PATCH 1/2] mount.cifs: update the cap bounding set only when CAP_SETPCAP is given

[Jonas Witschel <diabonas@archlinux.org>]

libcap-ng 0.8.1 tightened the error checking on capng_apply, returning an error
of -4 when trying to update the capability bounding set without having the
CAP_SETPCAP capability to be able to do so. Previous versions of libcap-ng
silently skipped updating the bounding set and only updated the normal
CAPNG_SELECT_CAPS capabilities instead.

Check beforehand whether we have CAP_SETPCAP, in which case we can use
CAPNG_SELECT_BOTH to update both the normal capabilities and the bounding set.
Otherwise, we can at least update the normal capabilities, but refrain from
trying to update the bounding set to avoid getting an error.

Signed-off-by: Jonas Witschel <diabonas@archlinux.org>
---
 mount.cifs.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/mount.cifs.c b/mount.cifs.c
index 4feb397..88b8b69 100644
--- a/mount.cifs.c
+++ b/mount.cifs.c
@@ -338,6 +338,8 @@ static int set_password(struct parsed_mount_info *parsed_info, const char *src)
 static int
 drop_capabilities(int parent)
 {
+	capng_select_t set = CAPNG_SELECT_CAPS;
+
 	capng_setpid(getpid());
 	capng_clear(CAPNG_SELECT_BOTH);
 	if (parent) {
@@ -355,7 +357,10 @@ drop_capabilities(int parent)
 			return EX_SYSERR;
 		}
 	}
-	if (capng_apply(CAPNG_SELECT_BOTH)) {
+	if (capng_have_capability(CAPNG_EFFECTIVE, CAP_SETPCAP)) {
+		set = CAPNG_SELECT_BOTH;
+	}
+	if (capng_apply(set)) {
 		fprintf(stderr, "Unable to apply new capability set.\n");
 		return EX_SYSERR;
 	}
-- 
2.29.2