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Date: Fri, 1 Mar 2024 18:29:39 +0300
From: Dan Carpenter <dan.carpenter@linaro.org>
To: Dylan Yudaken <dylany@fb.com>
Cc: Jens Axboe <axboe@kernel.dk>, Pavel Begunkov <asml.silence@gmail.com>,
	io-uring@vger.kernel.org, linux-kernel@vger.kernel.org,
	kernel-janitors@vger.kernel.org
Subject: [PATCH 1/2] io_uring/net: fix overflow check in
 io_recvmsg_mshot_prep()
Message-ID: <138bd2e2-ede8-4bcc-aa7b-f3d9de167a37@moroto.mountain>
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In-Reply-To: <7f5d7887-f76e-4e68-98c2-894bfedbf292@moroto.mountain>

The "controllen" variable is type size_t (unsigned long).  Casting it
to int could lead to an integer underflow.

The check_add_overflow() function considers the type of the destination
which is type int.  If we add two positive values and the result cannot
fit in an integer then that's counted as an overflow.

However, if we cast "controllen" to an int and it turns negative, then
negative values *can* fit into an int type so there is no overflow.

Good: 100 + (unsigned long)-4 = 96  <-- overflow
 Bad: 100 + (int)-4 = 96 <-- no overflow

I deleted the cast of the sizeof() as well.  That's not a bug but the
cast is unnecessary.

Fixes: 9b0fc3c054ff ("io_uring: fix types in io_recvmsg_multishot_overflow")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
---
 io_uring/net.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/io_uring/net.c b/io_uring/net.c
index 926d1fb0335d..da257bf429d5 100644
--- a/io_uring/net.c
+++ b/io_uring/net.c
@@ -559,10 +559,10 @@ static int io_recvmsg_mshot_prep(struct io_kiocb *req,
 
 		if (unlikely(namelen < 0))
 			return -EOVERFLOW;
-		if (check_add_overflow((int)sizeof(struct io_uring_recvmsg_out),
+		if (check_add_overflow(sizeof(struct io_uring_recvmsg_out),
 					namelen, &hdr))
 			return -EOVERFLOW;
-		if (check_add_overflow(hdr, (int)controllen, &hdr))
+		if (check_add_overflow(hdr, controllen, &hdr))
 			return -EOVERFLOW;
 
 		iomsg->namelen = namelen;
-- 
2.43.0