bus: drop creds->capability_size

The number of available caps can be read from
/proc/sys/kernel/cap_last_cap during runtime. Our helper cap_last_cap()
does that, so there's no reason to remember the size of any capability
cache. We can just pre-allocate arrays with a suitable size for all
available caps and reject any higher caps.

The kernel capability API uses u32 as base so make sure we do the same.
Note that this is specified by POSIX, so it's unlikely to change.

4 files changed, 25 insertions, 13 deletions

diff --git a/src/libsystemd/sd-bus/bus-control.c b/src/libsystemd/sd-bus/bus-control.c
index e86546c343..b2394db3eb 100644
--- a/src/libsystemd/sd-bus/bus-control.c
+++ b/src/libsystemd/sd-bus/bus-control.c
@@ -33,6 +33,7 @@
 #include "bus-control.h"
 #include "bus-bloom.h"
 #include "bus-util.h"
+#include "capability.h"
 #include "cgroup-util.h"
 
 _public_ int sd_bus_get_unique_name(sd_bus *bus, const char **unique) {
@@ -520,8 +521,11 @@ static int bus_populate_creds_from_items(
                              SD_BUS_CREDS_INHERITABLE_CAPS | SD_BUS_CREDS_BOUNDING_CAPS) & mask;
 
                         if (m) {
-                                c->capability_size = item->size - offsetof(struct kdbus_item, caps.caps);
-                                c->capability = memdup(item->caps.caps, c->capability_size);
+                                if (item->caps.last_cap != cap_last_cap() ||
+                                    item->size - offsetof(struct kdbus_item, caps.caps) < DIV_ROUND_UP(item->caps.last_cap, 32U) * 4 * 4)
+                                        return -EBADMSG;
+
+                                c->capability = memdup(item->caps.caps, item->size - offsetof(struct kdbus_item, caps.caps));
                                 if (!c->capability)
                                         return -ENOMEM;
 
diff --git a/src/libsystemd/sd-bus/bus-creds.c b/src/libsystemd/sd-bus/bus-creds.c
index 9978ddfa38..55d6fb6b43 100644
--- a/src/libsystemd/sd-bus/bus-creds.c
+++ b/src/libsystemd/sd-bus/bus-creds.c
@@ -22,6 +22,7 @@
 #include <stdlib.h>
 
 #include "util.h"
+#include "capability.h"
 #include "cgroup-util.h"
 #include "fileio.h"
 #include "audit.h"
@@ -588,10 +589,11 @@ static int has_cap(sd_bus_creds *c, unsigned offset, int capability) {
         size_t sz;
 
         assert(c);
+        assert(capability >= 0);
         assert(c->capability);
 
-        sz = c->capability_size / 4;
-        if ((size_t) capability >= sz*8)
+        sz = DIV_ROUND_UP(cap_last_cap(), 32U) * 4;
+        if ((unsigned)capability > cap_last_cap())
                 return 0;
 
         return !!(c->capability[offset * sz + (capability / 8)] & (1 << (capability % 8)));
@@ -638,12 +640,13 @@ _public_ int sd_bus_creds_has_bounding_cap(sd_bus_creds *c, int capability) {
 }
 
 static int parse_caps(sd_bus_creds *c, unsigned offset, const char *p) {
-        size_t sz;
+        size_t sz, max;
         unsigned i;
 
         assert(c);
         assert(p);
 
+        max = DIV_ROUND_UP(cap_last_cap(), 32U) * 4;
         p += strspn(p, WHITESPACE);
 
         sz = strlen(p);
@@ -651,12 +654,13 @@ static int parse_caps(sd_bus_creds *c, unsigned offset, const char *p) {
                 return -EINVAL;
 
         sz /= 2;
+        if (sz > max)
+                return -EINVAL;
+
         if (!c->capability) {
-                c->capability = new0(uint8_t, sz * 4);
+                c->capability = new0(uint8_t, max * 4);
                 if (!c->capability)
                         return -ENOMEM;
-
-                c->capability_size = sz * 4;
         }
 
         for (i = 0; i < sz; i ++) {
@@ -668,7 +672,7 @@ static int parse_caps(sd_bus_creds *c, unsigned offset, const char *p) {
                 if (x < 0 || y < 0)
                         return -EINVAL;
 
-                c->capability[offset * sz + (sz - i - 1)] = (uint8_t) x << 4 | (uint8_t) y;
+                c->capability[offset * max + (sz - i - 1)] = (uint8_t) x << 4 | (uint8_t) y;
         }
 
         return 0;
@@ -1073,11 +1077,10 @@ int bus_creds_extend_by_pid(sd_bus_creds *c, uint64_t mask, sd_bus_creds **ret)
         }
 
         if (c->mask & mask & (SD_BUS_CREDS_EFFECTIVE_CAPS|SD_BUS_CREDS_PERMITTED_CAPS|SD_BUS_CREDS_INHERITABLE_CAPS|SD_BUS_CREDS_BOUNDING_CAPS)) {
-                n->capability = memdup(c->capability, c->capability_size);
+                n->capability = memdup(c->capability, DIV_ROUND_UP(cap_last_cap(), 32U) * 4 * 4);
                 if (!n->capability)
                         return -ENOMEM;
 
-                n->capability_size = c->capability_size;
                 n->mask |= c->mask & mask & (SD_BUS_CREDS_EFFECTIVE_CAPS|SD_BUS_CREDS_PERMITTED_CAPS|SD_BUS_CREDS_INHERITABLE_CAPS|SD_BUS_CREDS_BOUNDING_CAPS);
         }
 
diff --git a/src/libsystemd/sd-bus/bus-creds.h b/src/libsystemd/sd-bus/bus-creds.h
index 48453e2afd..2480a4a0b1 100644
--- a/src/libsystemd/sd-bus/bus-creds.h
+++ b/src/libsystemd/sd-bus/bus-creds.h
@@ -61,7 +61,6 @@ struct sd_bus_creds {
         char *slice;
 
         uint8_t *capability;
-        size_t capability_size;
 
         uint32_t audit_session_id;
         uid_t audit_login_uid;
diff --git a/src/libsystemd/sd-bus/bus-kernel.c b/src/libsystemd/sd-bus/bus-kernel.c
index d9252b2560..eeb4a518d1 100644
--- a/src/libsystemd/sd-bus/bus-kernel.c
+++ b/src/libsystemd/sd-bus/bus-kernel.c
@@ -32,6 +32,7 @@
 #include "util.h"
 #include "strv.h"
 #include "memfd-util.h"
+#include "capability.h"
 #include "cgroup-util.h"
 #include "fileio.h"
 
@@ -673,8 +674,13 @@ static int bus_kernel_make_message(sd_bus *bus, struct kdbus_msg *k) {
                         break;
 
                 case KDBUS_ITEM_CAPS:
+                        if (d->caps.last_cap != cap_last_cap() ||
+                            d->size - offsetof(struct kdbus_item, caps.caps) < DIV_ROUND_UP(d->caps.last_cap, 32U) * 4 * 4) {
+                                r = -EBADMSG;
+                                goto fail;
+                        }
+
                         m->creds.capability = (uint8_t *) d->caps.caps;
-                        m->creds.capability_size = d->size - offsetof(struct kdbus_item, caps.caps);
                         m->creds.mask |= (SD_BUS_CREDS_EFFECTIVE_CAPS|SD_BUS_CREDS_PERMITTED_CAPS|SD_BUS_CREDS_INHERITABLE_CAPS|SD_BUS_CREDS_BOUNDING_CAPS) & bus->creds_mask;
                         break;