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From:   Max Kellermann <mk@cm4all.com>
To:     axboe@kernel.dk, linux-fsdevel@vger.kernel.org
Cc:     linux-kernel@vger.kernel.org, Max Kellermann <mk@cm4all.com>,
        stable@vger.kernel.org
Subject: [PATCH v2 1/2] fs/io_uring: fix O_PATH fds in openat, openat2, statx
Date:   Fri,  8 May 2020 08:38:45 +0200
Message-Id: <20200508063846.21067-1-mk@cm4all.com>
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Sender: linux-kernel-owner@vger.kernel.org
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If an operation's flag `needs_file` is set, the function
io_req_set_file() calls io_file_get() to obtain a `struct file*`.

This fails for `O_PATH` file descriptors, because io_file_get() calls
fget(), which rejects `O_PATH` file descriptors.  To support `O_PATH`,
fdget_raw() must be used (like path_init() in `fs/namei.c` does).
This rejection causes io_req_set_file() to throw `-EBADF`.  This
breaks the operations `openat`, `openat2` and `statx`, where `O_PATH`
file descriptors are commonly used.

This could be solved by adding support for `O_PATH` file descriptors
with another `io_op_def` flag, but since those three operations don't
need the `struct file*` but operate directly on the numeric file
descriptors, the best solution here is to simply remove `needs_file`
(and the accompanying flag `fd_non_reg`).

Signed-off-by: Max Kellermann <mk@cm4all.com>
Cc: stable@vger.kernel.org
---
 fs/io_uring.c | 6 ------
 1 file changed, 6 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index a46de2cfc28e..d24f8e33323c 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -693,8 +693,6 @@ static const struct io_op_def io_op_defs[] = {
 		.needs_file		= 1,
 	},
 	[IORING_OP_OPENAT] = {
-		.needs_file		= 1,
-		.fd_non_neg		= 1,
 		.file_table		= 1,
 		.needs_fs		= 1,
 	},
@@ -708,8 +706,6 @@ static const struct io_op_def io_op_defs[] = {
 	},
 	[IORING_OP_STATX] = {
 		.needs_mm		= 1,
-		.needs_file		= 1,
-		.fd_non_neg		= 1,
 		.needs_fs		= 1,
 	},
 	[IORING_OP_READ] = {
@@ -739,8 +735,6 @@ static const struct io_op_def io_op_defs[] = {
 		.unbound_nonreg_file	= 1,
 	},
 	[IORING_OP_OPENAT2] = {
-		.needs_file		= 1,
-		.fd_non_neg		= 1,
 		.file_table		= 1,
 		.needs_fs		= 1,
 	},
-- 
2.20.1