[lvc-project] [PATCH 6.12.y v2] cifs: Fix handling of a beyond-EOF DIO/unbuffered read over SMB1

[Mikhail Mirkin]

From: David Howells <dhowells at redhat.com>

commit 9d85ac939d52e93d80efb01a299c6f0bedb30487 upstream.

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 at redhat.com>
Reviewed-by: Paulo Alcantara (Red Hat) <pc at manguebit.org>
cc: Shyam Prasad N <sprasad at microsoft.com>
cc: linux-cifs at vger.kernel.org
cc: netfs at lists.linux.dev
cc: linux-fsdevel at vger.kernel.org
cc: lvc-project at linuxtesting.org
Signed-off-by: Steve French <stfrench at microsoft.com>
[Mikhail Mirkin: Adopted for 6.12]
Signed-off-by: Mikhail Mirkin <mmirkin at nppct.ru>
---
 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 01c78d9e7..11d408d1a 100644
--- a/fs/smb/client/cifssmb.c
+++ b/fs/smb/client/cifssmb.c
@@ -1321,7 +1321,7 @@ 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) {
 			__set_bit(NETFS_SREQ_HIT_EOF, &rdata->subreq.flags);
 			rdata->result = 0;
 		}
-- 
2.50.1