FAILED: patch "[PATCH] bpf: Allow LPM map access from sleepable BPF programs" failed to apply to 6.18-stable tree

FAILED: patch "[PATCH] bpf: Allow LPM map access from sleepable BPF programs" failed to apply to 6.18-stable tree

[gregkh]

The patch below does not apply to the 6.18-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.18.y
git checkout FETCH_HEAD
git cherry-pick -x 2f884d371fafea137afea504d49ee4a7c8d7985b
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2026071429-contort-navy-4802@gregkh' --subject-prefix 'PATCH 6.18.y' 'HEAD^..'

Possible dependencies:



thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 2f884d371fafea137afea504d49ee4a7c8d7985b Mon Sep 17 00:00:00 2001
From: Vlad Poenaru <vlad.wing@gmail.com>
Date: Tue, 9 Jun 2026 06:55:57 -0700
Subject: [PATCH] bpf: Allow LPM map access from sleepable BPF programs

trie_lookup_elem() annotates its rcu_dereference_check() walks with
only rcu_read_lock_bh_held().  Because rcu_dereference_check(p, c)
resolves to "c || rcu_read_lock_held()", this passes for XDP/NAPI and
classic RCU readers but fails for sleepable BPF programs, which enter
via __bpf_prog_enter_sleepable() and hold only rcu_read_lock_trace().

trie_update_elem() and trie_delete_elem() have the same problem in a
different form: they walk the trie with plain rcu_dereference(), which
asserts rcu_read_lock_held() unconditionally.  Both are reachable from
sleepable BPF programs via the bpf_map_update_elem / bpf_map_delete_elem
helpers, and from the syscall path under classic rcu_read_lock().  In
the writer paths the trie is actually protected by trie->lock (an
rqspinlock taken across the walk); we never relied on the RCU read-side
lock to keep nodes alive there.

A sleepable LSM hook that ends up touching an LPM trie therefore
triggers lockdep on debug kernels:

  =============================
  WARNING: suspicious RCU usage
  7.1.0-... Tainted: G            E
  -----------------------------
  kernel/bpf/lpm_trie.c:249 suspicious rcu_dereference_check() usage!
  1 lock held by net_tests/540:
   #0: (rcu_tasks_trace_srcu_struct){....}-{0:0},
       at: __bpf_prog_enter_sleepable+0x26/0x280
  Call Trace:
   dump_stack_lvl
   lockdep_rcu_suspicious
   trie_lookup_elem
   bpf_prog_..._enforce_security_socket_connect
   bpf_trampoline_...
   security_socket_connect
   __sys_connect
   do_syscall_64

This is lockdep-only -- no UAF, since Tasks Trace RCU does serialize
against the trie's reclaim path -- but it spams the console once per
distinct callsite on every debug kernel running a sleepable BPF LSM
that touches an LPM trie, which is increasingly common.

For the lookup path, switch the rcu_dereference_check() annotation
from rcu_read_lock_bh_held() to bpf_rcu_lock_held(), which accepts all
three contexts (classic, BH, Tasks Trace).  Other map types already
follow this convention.

For trie_update_elem() and trie_delete_elem(), annotate the walks as
rcu_dereference_protected(*p, 1) -- matching trie_free() in the same
file -- since trie->lock is held across the walk.  rqspinlock has no
lockdep_map, so the predicate degenerates to '1' rather than
lockdep_is_held(&trie->lock); the protection is real but not
machine-verifiable.  trie_get_next_key() also uses bare
rcu_dereference() but is reachable only from the BPF syscall, which
holds classic rcu_read_lock() before dispatching, so it is left
untouched.

Fixes: 694cea395fde ("bpf: Allow RCU-protected lookups to happen from bh context")
Cc: stable@vger.kernel.org
Signed-off-by: Vlad Poenaru <vlad.wing@gmail.com>
Reviewed-by: Emil Tsalapatis <emil@etsalapatis.com>
Link: https://lore.kernel.org/r/20260609135558.193287-2-vlad.wing@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

diff --git a/kernel/bpf/lpm_trie.c b/kernel/bpf/lpm_trie.c
index 0f57608b385d..4d6f25db9ba1 100644
--- a/kernel/bpf/lpm_trie.c
+++ b/kernel/bpf/lpm_trie.c
@@ -246,7 +246,7 @@ static void *trie_lookup_elem(struct bpf_map *map, void *_key)
 
 	/* Start walking the trie from the root node ... */
 
-	for (node = rcu_dereference_check(trie->root, rcu_read_lock_bh_held());
+	for (node = rcu_dereference_check(trie->root, bpf_rcu_lock_held());
 	     node;) {
 		unsigned int next_bit;
 		size_t matchlen;
@@ -280,7 +280,7 @@ static void *trie_lookup_elem(struct bpf_map *map, void *_key)
 		 */
 		next_bit = extract_bit(key->data, node->prefixlen);
 		node = rcu_dereference_check(node->child[next_bit],
-					     rcu_read_lock_bh_held());
+					     bpf_rcu_lock_held());
 	}
 
 	if (!found)
@@ -359,7 +359,7 @@ static long trie_update_elem(struct bpf_map *map,
 	 */
 	slot = &trie->root;
 
-	while ((node = rcu_dereference(*slot))) {
+	while ((node = rcu_dereference_protected(*slot, 1))) {
 		matchlen = longest_prefix_match(trie, node, key);
 
 		if (node->prefixlen != matchlen ||
@@ -482,7 +482,7 @@ static long trie_delete_elem(struct bpf_map *map, void *_key)
 	trim = &trie->root;
 	trim2 = trim;
 	parent = NULL;
-	while ((node = rcu_dereference(*trim))) {
+	while ((node = rcu_dereference_protected(*trim, 1))) {
 		matchlen = longest_prefix_match(trie, node, key);
 
 		if (node->prefixlen != matchlen ||

[PATCH 6.18.y 1/2] bpf: Consistently use bpf_rcu_lock_held() everywhere

[Sasha Levin]

From: Andrii Nakryiko <andrii@kernel.org>

[ Upstream commit 48a97ffc6c826640907d13b199e29008f4fe2c15 ]

We have many places which open-code what's now is bpf_rcu_lock_held()
macro, so replace all those places with a clean and short macro invocation.
For that, move bpf_rcu_lock_held() macro into include/linux/bpf.h.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Link: https://lore.kernel.org/bpf/20251014201403.4104511-1-andrii@kernel.org
Stable-dep-of: 2f884d371faf ("bpf: Allow LPM map access from sleepable BPF programs")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 include/linux/bpf.h               |  3 +++
 include/linux/bpf_local_storage.h |  3 ---
 kernel/bpf/hashtab.c              | 21 +++++++--------------
 kernel/bpf/helpers.c              | 12 ++++--------
 4 files changed, 14 insertions(+), 25 deletions(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index e2dd3a6d495afd..7ddc81cf77776a 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -2374,6 +2374,9 @@ bpf_prog_run_array_uprobe(const struct bpf_prog_array *array,
 bool bpf_jit_bypass_spec_v1(void);
 bool bpf_jit_bypass_spec_v4(void);
 
+#define bpf_rcu_lock_held() \
+	(rcu_read_lock_held() || rcu_read_lock_trace_held() || rcu_read_lock_bh_held())
+
 #ifdef CONFIG_BPF_SYSCALL
 DECLARE_PER_CPU(int, bpf_prog_active);
 extern struct mutex bpf_stats_enabled_mutex;
diff --git a/include/linux/bpf_local_storage.h b/include/linux/bpf_local_storage.h
index ab7244d8108f60..782f58feea3565 100644
--- a/include/linux/bpf_local_storage.h
+++ b/include/linux/bpf_local_storage.h
@@ -18,9 +18,6 @@
 
 #define BPF_LOCAL_STORAGE_CACHE_SIZE	16
 
-#define bpf_rcu_lock_held()                                                    \
-	(rcu_read_lock_held() || rcu_read_lock_trace_held() ||                 \
-	 rcu_read_lock_bh_held())
 struct bpf_local_storage_map_bucket {
 	struct hlist_head list;
 	raw_spinlock_t lock;
diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c
index 469bc48b25127b..7f8e029a6af8d7 100644
--- a/kernel/bpf/hashtab.c
+++ b/kernel/bpf/hashtab.c
@@ -669,8 +669,7 @@ static void *__htab_map_lookup_elem(struct bpf_map *map, void *key)
 	struct htab_elem *l;
 	u32 hash, key_size;
 
-	WARN_ON_ONCE(!rcu_read_lock_held() && !rcu_read_lock_trace_held() &&
-		     !rcu_read_lock_bh_held());
+	WARN_ON_ONCE(!bpf_rcu_lock_held());
 
 	key_size = map->key_size;
 
@@ -1104,8 +1103,7 @@ static long htab_map_update_elem(struct bpf_map *map, void *key, void *value,
 		/* unknown flags */
 		return -EINVAL;
 
-	WARN_ON_ONCE(!rcu_read_lock_held() && !rcu_read_lock_trace_held() &&
-		     !rcu_read_lock_bh_held());
+	WARN_ON_ONCE(!bpf_rcu_lock_held());
 
 	key_size = map->key_size;
 
@@ -1212,8 +1210,7 @@ static long htab_lru_map_update_elem(struct bpf_map *map, void *key, void *value
 		/* unknown flags */
 		return -EINVAL;
 
-	WARN_ON_ONCE(!rcu_read_lock_held() && !rcu_read_lock_trace_held() &&
-		     !rcu_read_lock_bh_held());
+	WARN_ON_ONCE(!bpf_rcu_lock_held());
 
 	key_size = map->key_size;
 
@@ -1281,8 +1278,7 @@ static long htab_map_update_elem_in_place(struct bpf_map *map, void *key,
 		/* unknown flags */
 		return -EINVAL;
 
-	WARN_ON_ONCE(!rcu_read_lock_held() && !rcu_read_lock_trace_held() &&
-		     !rcu_read_lock_bh_held());
+	WARN_ON_ONCE(!bpf_rcu_lock_held());
 
 	key_size = map->key_size;
 
@@ -1344,8 +1340,7 @@ static long __htab_lru_percpu_map_update_elem(struct bpf_map *map, void *key,
 		/* unknown flags */
 		return -EINVAL;
 
-	WARN_ON_ONCE(!rcu_read_lock_held() && !rcu_read_lock_trace_held() &&
-		     !rcu_read_lock_bh_held());
+	WARN_ON_ONCE(!bpf_rcu_lock_held());
 
 	key_size = map->key_size;
 
@@ -1422,8 +1417,7 @@ static long htab_map_delete_elem(struct bpf_map *map, void *key)
 	u32 hash, key_size;
 	int ret;
 
-	WARN_ON_ONCE(!rcu_read_lock_held() && !rcu_read_lock_trace_held() &&
-		     !rcu_read_lock_bh_held());
+	WARN_ON_ONCE(!bpf_rcu_lock_held());
 
 	key_size = map->key_size;
 
@@ -1458,8 +1452,7 @@ static long htab_lru_map_delete_elem(struct bpf_map *map, void *key)
 	u32 hash, key_size;
 	int ret;
 
-	WARN_ON_ONCE(!rcu_read_lock_held() && !rcu_read_lock_trace_held() &&
-		     !rcu_read_lock_bh_held());
+	WARN_ON_ONCE(!bpf_rcu_lock_held());
 
 	key_size = map->key_size;
 
diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index b5964524244814..3ce07b250ae085 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -42,8 +42,7 @@
  */
 BPF_CALL_2(bpf_map_lookup_elem, struct bpf_map *, map, void *, key)
 {
-	WARN_ON_ONCE(!rcu_read_lock_held() && !rcu_read_lock_trace_held() &&
-		     !rcu_read_lock_bh_held());
+	WARN_ON_ONCE(!bpf_rcu_lock_held());
 	return (unsigned long) map->ops->map_lookup_elem(map, key);
 }
 
@@ -59,8 +58,7 @@ const struct bpf_func_proto bpf_map_lookup_elem_proto = {
 BPF_CALL_4(bpf_map_update_elem, struct bpf_map *, map, void *, key,
 	   void *, value, u64, flags)
 {
-	WARN_ON_ONCE(!rcu_read_lock_held() && !rcu_read_lock_trace_held() &&
-		     !rcu_read_lock_bh_held());
+	WARN_ON_ONCE(!bpf_rcu_lock_held());
 	return map->ops->map_update_elem(map, key, value, flags);
 }
 
@@ -77,8 +75,7 @@ const struct bpf_func_proto bpf_map_update_elem_proto = {
 
 BPF_CALL_2(bpf_map_delete_elem, struct bpf_map *, map, void *, key)
 {
-	WARN_ON_ONCE(!rcu_read_lock_held() && !rcu_read_lock_trace_held() &&
-		     !rcu_read_lock_bh_held());
+	WARN_ON_ONCE(!bpf_rcu_lock_held());
 	return map->ops->map_delete_elem(map, key);
 }
 
@@ -134,8 +131,7 @@ const struct bpf_func_proto bpf_map_peek_elem_proto = {
 
 BPF_CALL_3(bpf_map_lookup_percpu_elem, struct bpf_map *, map, void *, key, u32, cpu)
 {
-	WARN_ON_ONCE(!rcu_read_lock_held() && !rcu_read_lock_trace_held() &&
-		     !rcu_read_lock_bh_held());
+	WARN_ON_ONCE(!bpf_rcu_lock_held());
 	return (unsigned long) map->ops->map_lookup_percpu_elem(map, key, cpu);
 }
 
-- 
2.53.0

[PATCH 6.18.y 2/2] bpf: Allow LPM map access from sleepable BPF programs

[Sasha Levin]

From: Vlad Poenaru <vlad.wing@gmail.com>

[ Upstream commit 2f884d371fafea137afea504d49ee4a7c8d7985b ]

trie_lookup_elem() annotates its rcu_dereference_check() walks with
only rcu_read_lock_bh_held().  Because rcu_dereference_check(p, c)
resolves to "c || rcu_read_lock_held()", this passes for XDP/NAPI and
classic RCU readers but fails for sleepable BPF programs, which enter
via __bpf_prog_enter_sleepable() and hold only rcu_read_lock_trace().

trie_update_elem() and trie_delete_elem() have the same problem in a
different form: they walk the trie with plain rcu_dereference(), which
asserts rcu_read_lock_held() unconditionally.  Both are reachable from
sleepable BPF programs via the bpf_map_update_elem / bpf_map_delete_elem
helpers, and from the syscall path under classic rcu_read_lock().  In
the writer paths the trie is actually protected by trie->lock (an
rqspinlock taken across the walk); we never relied on the RCU read-side
lock to keep nodes alive there.

A sleepable LSM hook that ends up touching an LPM trie therefore
triggers lockdep on debug kernels:

  =============================
  WARNING: suspicious RCU usage
  7.1.0-... Tainted: G            E
  -----------------------------
  kernel/bpf/lpm_trie.c:249 suspicious rcu_dereference_check() usage!
  1 lock held by net_tests/540:
   #0: (rcu_tasks_trace_srcu_struct){....}-{0:0},
       at: __bpf_prog_enter_sleepable+0x26/0x280
  Call Trace:
   dump_stack_lvl
   lockdep_rcu_suspicious
   trie_lookup_elem
   bpf_prog_..._enforce_security_socket_connect
   bpf_trampoline_...
   security_socket_connect
   __sys_connect
   do_syscall_64

This is lockdep-only -- no UAF, since Tasks Trace RCU does serialize
against the trie's reclaim path -- but it spams the console once per
distinct callsite on every debug kernel running a sleepable BPF LSM
that touches an LPM trie, which is increasingly common.

For the lookup path, switch the rcu_dereference_check() annotation
from rcu_read_lock_bh_held() to bpf_rcu_lock_held(), which accepts all
three contexts (classic, BH, Tasks Trace).  Other map types already
follow this convention.

For trie_update_elem() and trie_delete_elem(), annotate the walks as
rcu_dereference_protected(*p, 1) -- matching trie_free() in the same
file -- since trie->lock is held across the walk.  rqspinlock has no
lockdep_map, so the predicate degenerates to '1' rather than
lockdep_is_held(&trie->lock); the protection is real but not
machine-verifiable.  trie_get_next_key() also uses bare
rcu_dereference() but is reachable only from the BPF syscall, which
holds classic rcu_read_lock() before dispatching, so it is left
untouched.

Fixes: 694cea395fde ("bpf: Allow RCU-protected lookups to happen from bh context")
Cc: stable@vger.kernel.org
Signed-off-by: Vlad Poenaru <vlad.wing@gmail.com>
Reviewed-by: Emil Tsalapatis <emil@etsalapatis.com>
Link: https://lore.kernel.org/r/20260609135558.193287-2-vlad.wing@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 kernel/bpf/lpm_trie.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/kernel/bpf/lpm_trie.c b/kernel/bpf/lpm_trie.c
index be66d7e520e0d3..b05180661b736c 100644
--- a/kernel/bpf/lpm_trie.c
+++ b/kernel/bpf/lpm_trie.c
@@ -246,7 +246,7 @@ static void *trie_lookup_elem(struct bpf_map *map, void *_key)
 
 	/* Start walking the trie from the root node ... */
 
-	for (node = rcu_dereference_check(trie->root, rcu_read_lock_bh_held());
+	for (node = rcu_dereference_check(trie->root, bpf_rcu_lock_held());
 	     node;) {
 		unsigned int next_bit;
 		size_t matchlen;
@@ -280,7 +280,7 @@ static void *trie_lookup_elem(struct bpf_map *map, void *_key)
 		 */
 		next_bit = extract_bit(key->data, node->prefixlen);
 		node = rcu_dereference_check(node->child[next_bit],
-					     rcu_read_lock_bh_held());
+					     bpf_rcu_lock_held());
 	}
 
 	if (!found)
@@ -359,7 +359,7 @@ static long trie_update_elem(struct bpf_map *map,
 	 */
 	slot = &trie->root;
 
-	while ((node = rcu_dereference(*slot))) {
+	while ((node = rcu_dereference_protected(*slot, 1))) {
 		matchlen = longest_prefix_match(trie, node, key);
 
 		if (node->prefixlen != matchlen ||
@@ -482,7 +482,7 @@ static long trie_delete_elem(struct bpf_map *map, void *_key)
 	trim = &trie->root;
 	trim2 = trim;
 	parent = NULL;
-	while ((node = rcu_dereference(*trim))) {
+	while ((node = rcu_dereference_protected(*trim, 1))) {
 		matchlen = longest_prefix_match(trie, node, key);
 
 		if (node->prefixlen != matchlen ||
-- 
2.53.0