[libvirt] [PATCH] util: Call capng_setpid() before using cap-ng

[Andrea Bolognani]

audit is using cap-ng itself since version 2.6.1, and it gets
to initialize the internal state of the cap-ng library before
we call fork(). Because of that, our own use of cap-ng in the
child process ends up attempting to change the capabilities of
the parent process instead of the child process, which fails.

Calling capng_setpid() before using any other cap-ng API
ensures we're altering the capabilities of the right process.
---
 src/util/virutil.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/src/util/virutil.c b/src/util/virutil.c
index 170dd59..d393a12 100644
--- a/src/util/virutil.c
+++ b/src/util/virutil.c
@@ -1465,6 +1465,14 @@ virSetUIDGIDWithCaps(uid_t uid, gid_t gid, gid_t *groups, int ngroups,
     bool need_setgid = false, need_setuid = false;
     bool need_setpcap = false;
 
+    /* The cap-ng library stores some internal data in a thread local
+     * variable; that includes the PID of the process it should alter
+     * the capabilities of. After fork(), this data is not cleared,
+     * so we might end up trying to change the capabilities of a
+     * different process. Initialize the PID explicitly to work around
+     * that issue */
+    capng_setpid(getpid());
+
     /* First drop all caps (unless the requested uid is "unchanged" or
      * root and clearExistingCaps wasn't requested), then add back
      * those in capBits + the extra ones we need to change uid/gid and
-- 
2.7.4