Re: [REGRESSION 6.1.70] system calls with CIFS mounts failing with "Resource temporarily unavailable"

[Paulo Alcantara <pc@xxxxxxxxxxxxx>]

Hi Jan,

Thanks for the report.

So this bug is related to an off-by-one in smb2_set_next_command() when
the client attempts to pad SMB2_QUERY_INFO request -- since it isn't 8 byte
aligned -- even though smb2_query_info_compound() doesn't provide an extra
iov for such padding.

v6.1.y doesn't have

        eb3e28c1e89b ("smb3: Replace smb2pdu 1-element arrays with flex-arrays")

and the commit does

	+	if (unlikely(check_add_overflow(input_len, sizeof(*req), &len) ||
	+		     len > CIFSMaxBufSize))
	+		return -EINVAL;
	+

so sizeof(*req) will wrongly include the extra byte from
smb2_query_info_req::Buffer making @len unaligned and therefore causing
OOB in smb2_set_next_command().

A simple fix for that would be

	diff --git a/fs/smb/client/smb2pdu.c b/fs/smb/client/smb2pdu.c
	index 05ff8a457a3d..aed5067661de 100644
	--- a/fs/smb/client/smb2pdu.c
	+++ b/fs/smb/client/smb2pdu.c
	@@ -3556,7 +3556,7 @@ SMB2_query_info_init(struct cifs_tcon *tcon, struct TCP_Server_Info *server,
	 
	 	iov[0].iov_base = (char *)req;
	 	/* 1 for Buffer */
	-	iov[0].iov_len = len;
	+	iov[0].iov_len = len - 1;
	 	return 0;
	 }