[libvirt] [PATCH] util: fix clear_emulator_capabilities=0

[Laine Stump]

My commit 7a2e845a865dc7fa82d2393ea2a770cfc8cf00b4 (and its
prerequisites) managed to effectively ignore the
clear_emulator_capabilities setting in qemu.conf (visible in the code
as the VIR_EXEC_CLEAR_CAPS flag when qemu is being exec'ed), with the
result that the capabilities are always cleared regardless of the
qemu.conf setting. This patch fixes it by passing the flag through to
virSetUIDGIDWithCaps(), which uses it to decide whether or not to
clear existing capabilities before adding in those that were
requested.

Note that the existing capabilities are *always* cleared if the new
process is going to run as non-root, since the whole point of running
non-root is to have the capabilities removed (it's still possible to
add back individual capabilities as needed though).
---
This will need to be backported to v1.0.3-maint.

 src/util/vircommand.c |  4 +++-
 src/util/virutil.c    | 16 ++++++++++------
 src/util/virutil.h    |  3 ++-
 3 files changed, 15 insertions(+), 8 deletions(-)

diff --git a/src/util/vircommand.c b/src/util/vircommand.c
index f672101..08d3d29 100644
--- a/src/util/vircommand.c
+++ b/src/util/vircommand.c
@@ -639,8 +639,10 @@ virExec(virCommandPtr cmd)
         cmd->capabilities || (cmd->flags & VIR_EXEC_CLEAR_CAPS)) {
         VIR_DEBUG("Setting child uid:gid to %d:%d with caps %llx",
                   (int)cmd->uid, (int)cmd->gid, cmd->capabilities);
-        if (virSetUIDGIDWithCaps(cmd->uid, cmd->gid, cmd->capabilities) < 0)
+        if (virSetUIDGIDWithCaps(cmd->uid, cmd->gid, cmd->capabilities,
+                                 (cmd->flags & VIR_EXEC_CLEAR_CAPS)) < 0) {
             goto fork_error;
+        }
     }
 
     if (cmd->pwd) {
diff --git a/src/util/virutil.c b/src/util/virutil.c
index 4605c78..634b7e3 100644
--- a/src/util/virutil.c
+++ b/src/util/virutil.c
@@ -2998,18 +2998,21 @@ virGetGroupName(gid_t gid ATTRIBUTE_UNUSED)
  * errno).
  */
 int
-virSetUIDGIDWithCaps(uid_t uid, gid_t gid, unsigned long long capBits)
+virSetUIDGIDWithCaps(uid_t uid, gid_t gid, unsigned long long capBits,
+                     bool clearExistingCaps)
 {
     int ii, capng_ret, ret = -1;
     bool need_setgid = false, need_setuid = false;
     bool need_prctl = false, need_setpcap = false;
 
-    /* First drop all caps except those in capBits + the extra ones we
-     * need to change uid/gid and change the capabilities bounding
-     * set.
+    /* 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
+     * change the capabilities bounding set.
      */
 
-    capng_clear(CAPNG_SELECT_BOTH);
+    if (clearExistingCaps || (uid != 1 && uid != 0))
+       capng_clear(CAPNG_SELECT_BOTH);
 
     for (ii = 0; ii <= CAP_LAST_CAP; ii++) {
         if (capBits & (1ULL << ii)) {
@@ -3095,7 +3098,8 @@ cleanup:
 
 int
 virSetUIDGIDWithCaps(uid_t uid, gid_t gid,
-                     unsigned long long capBits ATTRIBUTE_UNUSED)
+                     unsigned long long capBits ATTRIBUTE_UNUSED,
+                     bool clearExistingCaps ATTRIBUTE_UNUSED)
 {
     return virSetUIDGID(uid, gid);
 }
diff --git a/src/util/virutil.h b/src/util/virutil.h
index 2dc3403..665ad78 100644
--- a/src/util/virutil.h
+++ b/src/util/virutil.h
@@ -54,7 +54,8 @@ int virPipeReadUntilEOF(int outfd, int errfd,
                         char **outbuf, char **errbuf);
 
 int virSetUIDGID(uid_t uid, gid_t gid);
-int virSetUIDGIDWithCaps(uid_t uid, gid_t gid, unsigned long long capBits);
+int virSetUIDGIDWithCaps(uid_t uid, gid_t gid, unsigned long long capBits,
+                         bool clearExistingCaps);
 
 int virFileReadLimFD(int fd, int maxlen, char **buf) ATTRIBUTE_RETURN_CHECK;
 
-- 
1.8.1.4