linux-kernel - [PATCH] io_uring/rw: Free iovec before cleaning async data

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Date: Thu, 30 May 2024 07:23:39 -0700
From: Breno Leitao <leitao@...ian.org>
To: Jens Axboe <axboe@...nel.dk>,
	Pavel Begunkov <asml.silence@...il.com>
Cc: leit@...a.com,
	io-uring@...r.kernel.org (open list:IO_URING),
	linux-kernel@...r.kernel.org (open list)
Subject: [PATCH] io_uring/rw: Free iovec before cleaning async data

kmemleak shows that there is a memory leak in io_uring read operation,
where a buffer is allocated at iovec import, but never de-allocated.

The memory is allocated at io_async_rw->free_iovec, but, then
io_async_rw is kfreed, taking the allocated memory with it. I saw this
happening when the read operation fails with -11 (EAGAIN).

This is the kmemleak splat.

    unreferenced object 0xffff8881da591c00 (size 256):
..
      backtrace (crc 7a15bdee):
	[<00000000256f2de4>] __kmalloc+0x2d6/0x410
	[<000000007a9f5fc7>] iovec_from_user.part.0+0xc6/0x160
	[<00000000cecdf83a>] __import_iovec+0x50/0x220
	[<00000000d1d586a2>] __io_import_iovec+0x13d/0x220
	[<0000000054ee9bd2>] io_prep_rw+0x186/0x340
	[<00000000a9c0372d>] io_prep_rwv+0x31/0x120
	[<000000001d1170b9>] io_prep_readv+0xe/0x30
	[<0000000070b8eb67>] io_submit_sqes+0x1bd/0x780
	[<00000000812496d4>] __do_sys_io_uring_enter+0x3ed/0x5b0
	[<0000000081499602>] do_syscall_64+0x5d/0x170
	[<00000000de1c5a4d>] entry_SYSCALL_64_after_hwframe+0x76/0x7e

This occurs because the async data cleanup functions are not set for
read/write operations. As a result, the potentially allocated iovec in
the rw async data is not freed before the async data is released,
leading to a memory leak.

With this following patch, kmemleak does not show the leaked memory
anymore, and all liburing tests pass.

Fixes: a9165b83c193 ("io_uring/rw: always setup io_async_rw for read/write requests")
Signed-off-by: Breno Leitao <leitao@...ian.org>
---
 io_uring/opdef.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/io_uring/opdef.c b/io_uring/opdef.c
index 2de5cca9504e..2e3b7b16effb 100644
--- a/io_uring/opdef.c
+++ b/io_uring/opdef.c
@@ -516,10 +516,12 @@ const struct io_cold_def io_cold_defs[] = {
 	},
 	[IORING_OP_READ_FIXED] = {
 		.name			= "READ_FIXED",
+		.cleanup		= io_readv_writev_cleanup,
 		.fail			= io_rw_fail,
 	},
 	[IORING_OP_WRITE_FIXED] = {
 		.name			= "WRITE_FIXED",
+		.cleanup		= io_readv_writev_cleanup,
 		.fail			= io_rw_fail,
 	},
 	[IORING_OP_POLL_ADD] = {
@@ -582,10 +584,12 @@ const struct io_cold_def io_cold_defs[] = {
 	},
 	[IORING_OP_READ] = {
 		.name			= "READ",
+		.cleanup		= io_readv_writev_cleanup,
 		.fail			= io_rw_fail,
 	},
 	[IORING_OP_WRITE] = {
 		.name			= "WRITE",
+		.cleanup		= io_readv_writev_cleanup,
 		.fail			= io_rw_fail,
 	},
 	[IORING_OP_FADVISE] = {
@@ -692,6 +696,7 @@ const struct io_cold_def io_cold_defs[] = {
 	},
 	[IORING_OP_READ_MULTISHOT] = {
 		.name			= "READ_MULTISHOT",
+		.cleanup		= io_readv_writev_cleanup,
 	},
 	[IORING_OP_WAITID] = {
 		.name			= "WAITID",
-- 
2.43.0