[for-linus][PATCH 4/5] tracing/remotes: Catch nr_page_va overflow in ring_buffer_desc sizing

[Steven Rostedt <rostedt@kernel.org>]

From: Vincent Donnefort <vdonnefort@google.com>

The number of pages per remote ring buffer is capped by
ring_buffer_desc::nr_page_va (32 bits). A buffer_size large enough to
overflow that field would silently allocate a descriptor smaller than
what was asked for.

Return SIZE_MAX from trace_buffer_desc_size() on nr_page_va overflow.

Link: https://patch.msgid.link/20260911193937.602202-3-vdonnefort@google.com
Fixes: 2e67fabd8b77 ("ring-buffer: Introduce ring-buffer remotes")
Signed-off-by: Vincent Donnefort <vdonnefort@google.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
 include/linux/ring_buffer.h | 4 ++++
 kernel/trace/trace_remote.c | 6 +++++-
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/include/linux/ring_buffer.h b/include/linux/ring_buffer.h
index 11bffb6a142d..eac3e9080c3c 100644
--- a/include/linux/ring_buffer.h
+++ b/include/linux/ring_buffer.h
@@ -295,6 +295,10 @@ static inline size_t trace_buffer_desc_size(size_t buffer_size, unsigned int nr_
 	unsigned long nr_pages = __calc_nr_pages_ring_buffer_desc(buffer_size);
 	struct ring_buffer_desc *rbdesc;
 
+	/* Capped by ring_buffer_desc::nr_page_va */
+	if (nr_pages > UINT_MAX)
+		return SIZE_MAX;
+
 	return size_add(offsetof(struct trace_buffer_desc, __data),
 			size_mul(nr_cpus, struct_size(rbdesc, page_va, nr_pages)));
 }
diff --git a/kernel/trace/trace_remote.c b/kernel/trace/trace_remote.c
index c17902e42ef1..2d5bc423efca 100644
--- a/kernel/trace/trace_remote.c
+++ b/kernel/trace/trace_remote.c
@@ -980,9 +980,12 @@ int trace_remote_alloc_buffer(struct trace_buffer_desc *desc, size_t desc_size,
 			      const struct cpumask *cpumask)
 {
 	size_t min_desc_size = trace_buffer_desc_size(buffer_size, cpumask_weight(cpumask));
-	unsigned int nr_pages = __calc_nr_pages_ring_buffer_desc(buffer_size);
 	struct ring_buffer_desc *rb_desc;
 	int cpu, ret = -ENOMEM;
+	unsigned int nr_pages;
+
+	if (min_desc_size == SIZE_MAX)
+		return -E2BIG;
 
 	if (desc_size < min_desc_size)
 		return -EINVAL;
@@ -991,6 +994,7 @@ int trace_remote_alloc_buffer(struct trace_buffer_desc *desc, size_t desc_size,
 	desc->struct_len = min_desc_size;
 
 	rb_desc = __first_ring_buffer_desc(desc);
+	nr_pages = __calc_nr_pages_ring_buffer_desc(buffer_size);
 
 	for_each_cpu(cpu, cpumask) {
 		unsigned int id;
-- 
2.53.0