[PATCH 2/2] virSetUIDGIDWithCaps: Set bounding capabilities only with CAP_SETPCAP

[Michal Privoznik]

In one of my previous patches I've tried to postpone dropping
CAP_SETPCAP until the very end because it's needed for
capng_apply(). What I did not realize back then was that we might
not have the capability to begin with. Because of unknown reasons
capng_apply() pollutes logs only for CAPNG_SELECT_BOUNDS and not
for CAPNG_SELECT_CAPS.

Reproducer is really simple: run libvirtd as a regular user.
During its initialization, libvirtd will spawn some binaries
(dnsmasq, qemu-*, etc.) and while doing so it will try to drop
capabilities.

Anyway, let's call capng_apply(CAPNG_SELECT_BOUNDS) only if we
have the CAP_SETPCAP (which is tracked in need_setpcap variable).

Fixes: 438b50dda8a863fdc988e9ab612f097cc1626e8a
Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1924218
Signed-off-by: Michal Privoznik <mprivozn at redhat.com>
---
 src/util/virutil.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/util/virutil.c b/src/util/virutil.c
index aba0aea0ff..00cd56e2b2 100644
--- a/src/util/virutil.c
+++ b/src/util/virutil.c
@@ -1250,7 +1250,8 @@ virSetUIDGIDWithCaps(uid_t uid, gid_t gid, gid_t *groups, int ngroups,
      * do this if we failed to get the capability above, so ignore the
      * return value.
      */
-    capng_apply(CAPNG_SELECT_BOUNDS);
+    if (!need_setpcap)
+        capng_apply(CAPNG_SELECT_BOUNDS);
 
     /* Drop the caps that allow setuid/gid (unless they were requested) */
     if (need_setgid)
-- 
2.31.1