linux-kernel - Re: [PATCH] cifs: Fix handling of a beyond-EOF DIO/unbuffered read over SMB2

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Message-ID: <d519f5eb5d5072dca8a06c4e127b1a0c@manguebit.org>
Date: Wed, 03 Dec 2025 19:46:07 -0300
From: Paulo Alcantara <pc@...guebit.org>
To: David Howells <dhowells@...hat.com>, Steve French <sfrench@...ba.org>
Cc: dhowells@...hat.com, Shyam Prasad N <sprasad@...rosoft.com>,
 linux-cifs@...r.kernel.org, netfs@...ts.linux.dev,
 linux-fsdevel@...r.kernel.org, stable@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH] cifs: Fix handling of a beyond-EOF DIO/unbuffered read
 over SMB2

David Howells <dhowells@...hat.com> writes:

> If a DIO read or an unbuffered read request extends beyond the EOF, the
> server will return a short read and a status code indicating that EOF was
> hit, which gets translated to -ENODATA.  Note that the client does not cap
> the request at i_size, but asks for the amount requested in case there's a
> race on the server with a third party.
>
> Now, on the client side, the request will get split into multiple
> subrequests if rsize is smaller than the full request size.  A subrequest
> that starts before or at the EOF and returns short data up to the EOF will
> be correctly handled, with the NETFS_SREQ_HIT_EOF flag being set,
> indicating to netfslib that we can't read more.
>
> If a subrequest, however, starts after the EOF and not at it, HIT_EOF will
> not be flagged, its error will be set to -ENODATA and it will be abandoned.
> This will cause the request as a whole to fail with -ENODATA.
>
> Fix this by setting NETFS_SREQ_HIT_EOF on any subrequest that lies beyond
> the EOF marker.
>
> Fixes: 1da29f2c39b6 ("netfs, cifs: Fix handling of short DIO read")
> Signed-off-by: David Howells <dhowells@...hat.com>
> cc: Steve French <sfrench@...ba.org>
> cc: Paulo Alcantara <pc@...guebit.org>
> cc: Shyam Prasad N <sprasad@...rosoft.com>
> cc: linux-cifs@...r.kernel.org
> cc: netfs@...ts.linux.dev
> cc: linux-fsdevel@...r.kernel.org

Reviewed-by: Paulo Alcantara (Red Hat) <pc@...guebit.org>