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Subject[PATCH][next] xen/xenbus: Add __counted_by for struct read_buffer and use struct_size()
Prepare for the coming implementation by GCC and Clang of the __counted_by
attribute. Flexible array members annotated with __counted_by can have
their accesses bounds-checked at run-time via CONFIG_UBSAN_BOUNDS (for
array indexing) and CONFIG_FORTIFY_SOURCE (for strcpy/memcpy-family
functions).

While there, use struct_size() helper, instead of the open-coded
version, to calculate the size for the allocation of the whole
flexible structure, including of course, the flexible-array member.

This code was found with the help of Coccinelle, and audited and
fixed manually.

Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
---
drivers/xen/xenbus/xenbus_dev_frontend.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/xen/xenbus/xenbus_dev_frontend.c b/drivers/xen/xenbus/xenbus_dev_frontend.c
index 0792fda49a15..6f56640092a9 100644
--- a/drivers/xen/xenbus/xenbus_dev_frontend.c
+++ b/drivers/xen/xenbus/xenbus_dev_frontend.c
@@ -82,7 +82,7 @@ struct read_buffer {
struct list_head list;
unsigned int cons;
unsigned int len;
- char msg[];
+ char msg[] __counted_by(len);
};

struct xenbus_file_priv {
@@ -195,7 +195,7 @@ static int queue_reply(struct list_head *queue, const void *data, size_t len)
if (len > XENSTORE_PAYLOAD_MAX)
return -EINVAL;

- rb = kmalloc(sizeof(*rb) + len, GFP_KERNEL);
+ rb = kmalloc(struct_size(rb, msg, len), GFP_KERNEL);
if (rb == NULL)
return -ENOMEM;

--
2.34.1
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