Merge tag 'for-netdev' of https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf

Daniel Borkmann says:

====================
pull-request: bpf 2023-11-08

We've added 16 non-merge commits during the last 6 day(s) which contain
a total of 30 files changed, 341 insertions(+), 130 deletions(-).

The main changes are:

1) Fix a BPF verifier issue in precision tracking for BPF_ALU | BPF_TO_BE |
   BPF_END where the source register was incorrectly marked as precise,
   from Shung-Hsi Yu.

2) Fix a concurrency issue in bpf_timer where the former could still have
   been alive after an application releases or unpins the map, from Hou Tao.

3) Fix a BPF verifier issue where immediates are incorrectly cast to u32
   before being spilled and therefore losing sign information, from Hao Sun.

4) Fix a misplaced BPF_TRACE_ITER in check_css_task_iter_allowlist which
   incorrectly compared bpf_prog_type with bpf_attach_type, from Chuyi Zhou.

5) Add __bpf_hook_{start,end} as well as __bpf_kfunc_{start,end}_defs macros,
   migrate all BPF-related __diag callsites over to it, and add a new
   __diag_ignore_all for -Wmissing-declarations to the macros to address
   recent build warnings, from Dave Marchevsky.

6) Fix broken BPF selftest build of xdp_hw_metadata test on architectures
   where char is not signed, from Björn Töpel.

7) Fix test_maps selftest to properly use LIBBPF_OPTS() macro to initialize
   the bpf_map_create_opts, from Andrii Nakryiko.

8) Fix bpffs selftest to avoid unmounting /sys/kernel/debug as it may have
   been mounted and used by other applications already, from Manu Bretelle.

9) Fix a build issue without CONFIG_CGROUPS wrt css_task open-coded
   iterators, from Matthieu Baerts.

* tag 'for-netdev' of https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf:
  selftests/bpf: get trusted cgrp from bpf_iter__cgroup directly
  bpf: Let verifier consider {task,cgroup} is trusted in bpf_iter_reg
  selftests/bpf: Fix broken build where char is unsigned
  selftests/bpf: precision tracking test for BPF_NEG and BPF_END
  bpf: Fix precision tracking for BPF_ALU | BPF_TO_BE | BPF_END
  selftests/bpf: Add test for using css_task iter in sleepable progs
  selftests/bpf: Add tests for css_task iter combining with cgroup iter
  bpf: Relax allowlist for css_task iter
  selftests/bpf: fix test_maps' use of bpf_map_create_opts
  bpf: Check map->usercnt after timer->timer is assigned
  bpf: Add __bpf_hook_{start,end} macros
  bpf: Add __bpf_kfunc_{start,end}_defs macros
  selftests/bpf: fix test_bpffs
  selftests/bpf: Add test for immediate spilled to stack
  bpf: Fix check_stack_write_fixed_off() to correctly spill imm
  bpf: fix compilation error without CGROUPS
====================

Link: https://lore.kernel.org/r/20231108132448.1970-1-daniel@iogearbox.net
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

1 files changed, 23 insertions, 16 deletions

diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index e46ac288a108..56b0c1f678ee 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -1177,13 +1177,6 @@ BPF_CALL_3(bpf_timer_init, struct bpf_timer_kern *, timer, struct bpf_map *, map
 		ret = -EBUSY;
 		goto out;
 	}
-	if (!atomic64_read(&map->usercnt)) {
-		/* maps with timers must be either held by user space
-		 * or pinned in bpffs.
-		 */
-		ret = -EPERM;
-		goto out;
-	}
 	/* allocate hrtimer via map_kmalloc to use memcg accounting */
 	t = bpf_map_kmalloc_node(map, sizeof(*t), GFP_ATOMIC, map->numa_node);
 	if (!t) {
@@ -1196,7 +1189,21 @@ BPF_CALL_3(bpf_timer_init, struct bpf_timer_kern *, timer, struct bpf_map *, map
 	rcu_assign_pointer(t->callback_fn, NULL);
 	hrtimer_init(&t->timer, clockid, HRTIMER_MODE_REL_SOFT);
 	t->timer.function = bpf_timer_cb;
-	timer->timer = t;
+	WRITE_ONCE(timer->timer, t);
+	/* Guarantee the order between timer->timer and map->usercnt. So
+	 * when there are concurrent uref release and bpf timer init, either
+	 * bpf_timer_cancel_and_free() called by uref release reads a no-NULL
+	 * timer or atomic64_read() below returns a zero usercnt.
+	 */
+	smp_mb();
+	if (!atomic64_read(&map->usercnt)) {
+		/* maps with timers must be either held by user space
+		 * or pinned in bpffs.
+		 */
+		WRITE_ONCE(timer->timer, NULL);
+		kfree(t);
+		ret = -EPERM;
+	}
 out:
 	__bpf_spin_unlock_irqrestore(&timer->lock);
 	return ret;
@@ -1374,7 +1381,7 @@ void bpf_timer_cancel_and_free(void *val)
 	/* The subsequent bpf_timer_start/cancel() helpers won't be able to use
 	 * this timer, since it won't be initialized.
 	 */
-	timer->timer = NULL;
+	WRITE_ONCE(timer->timer, NULL);
 out:
 	__bpf_spin_unlock_irqrestore(&timer->lock);
 	if (!t)
@@ -1886,9 +1893,7 @@ void bpf_rb_root_free(const struct btf_field *field, void *rb_root,
 	}
 }
 
-__diag_push();
-__diag_ignore_all("-Wmissing-prototypes",
-		  "Global functions as their definitions will be in vmlinux BTF");
+__bpf_kfunc_start_defs();
 
 __bpf_kfunc void *bpf_obj_new_impl(u64 local_type_id__k, void *meta__ign)
 {
@@ -2505,7 +2510,7 @@ __bpf_kfunc void bpf_throw(u64 cookie)
 	WARN(1, "A call to BPF exception callback should never return\n");
 }
 
-__diag_pop();
+__bpf_kfunc_end_defs();
 
 BTF_SET8_START(generic_btf_ids)
 #ifdef CONFIG_KEXEC_CORE
@@ -2564,15 +2569,17 @@ BTF_ID_FLAGS(func, bpf_iter_num_destroy, KF_ITER_DESTROY)
 BTF_ID_FLAGS(func, bpf_iter_task_vma_new, KF_ITER_NEW | KF_RCU)
 BTF_ID_FLAGS(func, bpf_iter_task_vma_next, KF_ITER_NEXT | KF_RET_NULL)
 BTF_ID_FLAGS(func, bpf_iter_task_vma_destroy, KF_ITER_DESTROY)
+#ifdef CONFIG_CGROUPS
 BTF_ID_FLAGS(func, bpf_iter_css_task_new, KF_ITER_NEW | KF_TRUSTED_ARGS)
 BTF_ID_FLAGS(func, bpf_iter_css_task_next, KF_ITER_NEXT | KF_RET_NULL)
 BTF_ID_FLAGS(func, bpf_iter_css_task_destroy, KF_ITER_DESTROY)
-BTF_ID_FLAGS(func, bpf_iter_task_new, KF_ITER_NEW | KF_TRUSTED_ARGS | KF_RCU_PROTECTED)
-BTF_ID_FLAGS(func, bpf_iter_task_next, KF_ITER_NEXT | KF_RET_NULL)
-BTF_ID_FLAGS(func, bpf_iter_task_destroy, KF_ITER_DESTROY)
 BTF_ID_FLAGS(func, bpf_iter_css_new, KF_ITER_NEW | KF_TRUSTED_ARGS | KF_RCU_PROTECTED)
 BTF_ID_FLAGS(func, bpf_iter_css_next, KF_ITER_NEXT | KF_RET_NULL)
 BTF_ID_FLAGS(func, bpf_iter_css_destroy, KF_ITER_DESTROY)
+#endif
+BTF_ID_FLAGS(func, bpf_iter_task_new, KF_ITER_NEW | KF_TRUSTED_ARGS | KF_RCU_PROTECTED)
+BTF_ID_FLAGS(func, bpf_iter_task_next, KF_ITER_NEXT | KF_RET_NULL)
+BTF_ID_FLAGS(func, bpf_iter_task_destroy, KF_ITER_DESTROY)
 BTF_ID_FLAGS(func, bpf_dynptr_adjust)
 BTF_ID_FLAGS(func, bpf_dynptr_is_null)
 BTF_ID_FLAGS(func, bpf_dynptr_is_rdonly)