[PATCH v2 2/3] tracing/remotes: Catch nr_page_va overflow in ring_buffer_desc sizing

[Vincent Donnefort]

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.

Fixes: 2e67fabd8b77 ("ring-buffer: Introduce ring-buffer remotes")
Signed-off-by: Vincent Donnefort <vdonnef...@google.com>
---
 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;
-- 
2.55.0.1007.g17ff1f9808-goog