util: add list of capabilities

the capsh approach doesn't work on RHEL as the version of libcap is not
updated and doesn't know all the possible capabilities available on the
system.  This is the output I get with getpcaps on RHELAH 7.4.2:

Capabilities for `1': = cap_chown,cap_dac_override,cap_dac_read_search,cap_fowner,cap_fsetid,cap_kill,cap_setgid,cap_setuid,cap_setpcap,cap_linux_immutable,cap_net_bind_service,cap_net_broadcast,cap_net_admin,cap_net_raw,cap_ipc_lock,cap_ipc_owner,cap_sys_module,cap_sys_rawio,cap_sys_chroot,cap_sys_ptrace,cap_sys_pacct,cap_sys_admin,cap_sys_boot,cap_sys_nice,cap_sys_resource,cap_sys_time,cap_sys_tty_config,cap_mknod,cap_lease,cap_audit_write,cap_audit_control,cap_setfcap,cap_mac_override,cap_mac_admin,cap_syslog,35,36+ep

Fallback to the capsh method if there will be more capabilities that we
know of, and hopefully libcap does.

Signed-off-by: Giuseppe Scrivano <[email protected]>

Closes: #1130
Approved by: rhatdan

Atomic/util.py

@@ -1136,6 +1136,45 @@ def remove_skopeo_prefixes(image):
             image = image.replace(remove, '')
     return image
 
+KNOWN_CAPS = ['CAP_CHOWN',
+              'CAP_DAC_OVERRIDE',
+              'CAP_DAC_READ_SEARCH',
+              'CAP_FOWNER',
+              'CAP_FSETID',
+              'CAP_KILL',
+              'CAP_SETGID',
+              'CAP_SETUID',
+              'CAP_SETPCAP',
+              'CAP_LINUX_IMMUTABLE',
+              'CAP_NET_BIND_SERVICE',
+              'CAP_NET_BROADCAST',
+              'CAP_NET_ADMIN',
+              'CAP_NET_RAW',
+              'CAP_IPC_LOCK',
+              'CAP_IPC_OWNER',
+              'CAP_SYS_MODULE',
+              'CAP_SYS_RAWIO',
+              'CAP_SYS_CHROOT',
+              'CAP_SYS_PTRACE',
+              'CAP_SYS_PACCT',
+              'CAP_SYS_ADMIN',
+              'CAP_SYS_BOOT',
+              'CAP_SYS_NICE',
+              'CAP_SYS_RESOURCE',
+              'CAP_SYS_TIME',
+              'CAP_SYS_TTY_CONFIG',
+              'CAP_MKNOD',
+              'CAP_LEASE',
+              'CAP_AUDIT_WRITE',
+              'CAP_AUDIT_CONTROL',
+              'CAP_SETFCAP',
+              'CAP_MAC_OVERRIDE',
+              'CAP_MAC_ADMIN',
+              'CAP_SYSLOG',
+              'CAP_WAKE_ALARM',
+              'CAP_BLOCK_SUSPEND',
+              'CAP_AUDIT_READ']
+
 def get_all_known_process_capabilities():
     """
     Get all the known process capabilities
@@ -1147,14 +1186,16 @@ def get_all_known_process_capabilities():
     with open("/proc/sys/kernel/cap_last_cap", 'r') as f:
         last_cap = int(f.read())
 
-    mask = hex((1 << (last_cap + 1)) - 1)
-
-    out = subprocess.check_output([CAPSH_PATH, '--decode={}'.format(mask)], stderr=DEVNULL)
+    if last_cap < len(KNOWN_CAPS):
+        caps = KNOWN_CAPS[:last_cap+1]
+    else:
+        mask = hex((1 << (last_cap + 1)) - 1)
+        out = subprocess.check_output([CAPSH_PATH, '--decode={}'.format(mask)], stderr=DEVNULL)
 
-    # The output looks like 0x0000003fffffffff=cap_chown,cap_dac_override,...
-    # so take only the part after the '='
-    caps = str(out.decode().split("=")[1].strip())
+        # The output looks like 0x0000003fffffffff=cap_chown,cap_dac_override,...
+        # so take only the part after the '='
+        caps = str(out.decode().split("=")[1].strip()).split(',')
 
-    caps_list = [i.upper() for i in caps.split(',')]
+    caps_list = [i.upper() for i in caps]
 
     return [i for i in caps_list if not i[0].isdigit()]