linux-kernel - [PATCH 5.10 02/97] io_uring: always grab file table for deferred statx

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Date:   Mon, 23 May 2022 19:05:06 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Lee Jones <lee.jones@...aro.org>,
        Jens Axboe <axboe@...nel.dk>
Subject: [PATCH 5.10 02/97] io_uring: always grab file table for deferred statx

From: Jens Axboe <axboe@...nel.dk>

Lee reports that there's a use-after-free of the process file table.
There's an assumption that we don't need the file table for some
variants of statx invocation, but that turns out to be false and we
end up with not grabbing a reference for the request even if the
deferred execution uses it.

Get rid of the REQ_F_NO_FILE_TABLE optimization for statx, and always
grab that reference.

This issues doesn't exist upstream since the native workers got
introduced with 5.12.

Link: https://lore.kernel.org/io-uring/YoOJ%2FT4QRKC+fAZE@google.com/
Reported-by: Lee Jones <lee.jones@...aro.org>
Signed-off-by: Jens Axboe <axboe@...nel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 fs/io_uring.c |    6 +-----
 1 file changed, 1 insertion(+), 5 deletions(-)

--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -4252,12 +4252,8 @@ static int io_statx(struct io_kiocb *req
 	struct io_statx *ctx = &req->statx;
 	int ret;
 
-	if (force_nonblock) {
-		/* only need file table for an actual valid fd */
-		if (ctx->dfd == -1 || ctx->dfd == AT_FDCWD)
-			req->flags |= REQ_F_NO_FILE_TABLE;
+	if (force_nonblock)
 		return -EAGAIN;
-	}
 
 	ret = do_statx(ctx->dfd, ctx->filename, ctx->flags, ctx->mask,
 		       ctx->buffer);