linux-kernel - [PATCH] cifs: Fix handling of a beyond-EOF DIO/unbuffered read over SMB1

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Message-ID: <1597479.1764697506@warthog.procyon.org.uk>
Date: Tue, 02 Dec 2025 17:45:06 +0000
From: David Howells <dhowells@...hat.com>
To: Steve French <sfrench@...ba.org>
cc: dhowells@...hat.com, Paulo Alcantara <pc@...guebit.org>,
    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: [PATCH] cifs: Fix handling of a beyond-EOF DIO/unbuffered read over SMB1

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.

This can be reproduced by mounting with "cache=none,sign,vers=1.0" and
doing a read of a file that's significantly bigger than the size of the
file (e.g. attempting to read 64KiB from a 16KiB file).

Fixes: a68c74865f51 ("cifs: Fix SMB1 readv/writev callback in the same way as SMB2/3")
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
---
 fs/smb/client/cifssmb.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/smb/client/cifssmb.c b/fs/smb/client/cifssmb.c
index 645831708e1b..1871d2c1a8e0 100644
--- a/fs/smb/client/cifssmb.c
+++ b/fs/smb/client/cifssmb.c
@@ -1395,7 +1395,7 @@ cifs_readv_callback(struct mid_q_entry *mid)
 	} else {
 		size_t trans = rdata->subreq.transferred + rdata->got_bytes;
 		if (trans < rdata->subreq.len &&
-		    rdata->subreq.start + trans == ictx->remote_i_size) {
+		    rdata->subreq.start + trans >= ictx->remote_i_size) {
 			rdata->result = 0;
 			__set_bit(NETFS_SREQ_HIT_EOF, &rdata->subreq.flags);
 		} else if (rdata->got_bytes > 0) {