linux-kernel - [PATCH 5.17 1055/1126] io_uring: bump poll refs to full 31-bits

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Message-Id: <20220405070438.432743258@linuxfoundation.org>
Date:   Tue,  5 Apr 2022 09:30:02 +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, Jens Axboe <axboe@...nel.dk>
Subject: [PATCH 5.17 1055/1126] io_uring: bump poll refs to full 31-bits

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

commit e2c0cb7c0cc72939b61a7efee376206725796625 upstream.

The previous commit:

1bc84c40088 ("io_uring: remove poll entry from list when canceling all")

removed a potential overflow condition for the poll references. They
are currently limited to 20-bits, even if we have 31-bits available. The
upper bit is used to mark for cancelation.

Bump the poll ref space to 31-bits, making that kind of situation much
harder to trigger in general. We'll separately add overflow checking
and handling.

Fixes: aa43477b0402 ("io_uring: poll rework")
Signed-off-by: Jens Axboe <axboe@...nel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 fs/io_uring.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -5414,7 +5414,7 @@ struct io_poll_table {
 };

 #define IO_POLL_CANCEL_FLAG	BIT(31)
-#define IO_POLL_REF_MASK	((1u << 20)-1)
+#define IO_POLL_REF_MASK	GENMASK(30, 0)

 /*
  * If refs part of ->poll_refs (see IO_POLL_REF_MASK) is 0, it's free. We can