[PATCH] io_uring/query: cap user size passed to copy_struct_to_user

From: Laxman Acharya Padhya <[email protected]>

io_handle_query_entry() clamps hdr.size for the inbound copy_from_user()
but keeps the original user value as usize. copy_struct_to_user() uses
that usize and, when it is larger than the kernel result, clear_user()s
the trailing bytes.

As hdr.size is a __u32, a query can request nearly 4 GiB of zeroing,
including on the error path where res_size stays 0. The interface is
reachable without a ring via IORING_REGISTER_QUERY.

Reject sizes larger than PAGE_SIZE, as recommended for copy_struct_*
interfaces.

Fixes: c265ae75f900 ("io_uring: introduce io_uring querying")
Cc: [email protected] # 6.18+
Signed-off-by: Laxman Acharya Padhya <[email protected]>
---
 io_uring/query.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/io_uring/query.c b/io_uring/query.c
index 88a325736992..f2b5e19e5af6 100644
--- a/io_uring/query.c
+++ b/io_uring/query.c
@@ -76,6 +76,9 @@ static int io_handle_query_entry(union io_query_data *data, void __user *uhdr,
 
 	if (copy_from_user(&hdr, uhdr, sizeof(hdr)))
 		return -EFAULT;
+	/* copy_struct_to_user() zeros up to usize bytes */
+	if (hdr.size > PAGE_SIZE)
+		return -E2BIG;
 	usize = hdr.size;
 	hdr.size = min(hdr.size, IO_MAX_QUERY_SIZE);
 	udata = u64_to_user_ptr(hdr.query_data);
-- 
2.51.2