[PATCH v3 1/2] smb: client: reject short READ responses in CIFSSMBRead()

[Diego Oliva]

CIFSSMBRead() reads DataLengthHigh, DataLength and DataOffset out of
the READ_RSP returned by the server without first checking that a
whole READ_RSP was actually received. The length of the response is
recorded in rsp_iov.iov_len, but nothing constrains it to be at least
read_rsp_size before those fields are dereferenced.

A malicious or compromised SMB1 server can return a response shorter
than the READ_RSP header, so that parsing the header itself reads past
the end of the receive buffer. SMB1 is not negotiated by default;
reaching this code requires an explicit vers=1.0 mount.

Reject the response unless it is at least read_rsp_size bytes long.

smb_EIO2() was introduced in v6.19, so this does not apply to older
stable trees without returning plain -EIO instead.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Suggested-by: Paulo Alcantara <pc@xxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> # 6.19.x
Assisted-by: Bynario AI
Signed-off-by: Diego Oliva <diego@xxxxxxxx>
---
 fs/smb/client/cifssmb.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/fs/smb/client/cifssmb.c b/fs/smb/client/cifssmb.c
index f5aad5f61dce..aa6b904ad866 100644
--- a/fs/smb/client/cifssmb.c
+++ b/fs/smb/client/cifssmb.c
@@ -1719,6 +1719,14 @@ CIFSSMBRead(const unsigned int xid, struct cifs_io_parms *io_parms,
 	pSMBr = (READ_RSP *)rsp_iov.iov_base;
 	if (rc) {
 		cifs_dbg(VFS, "Send error in read = %d\n", rc);
+	} else if (rsp_iov.iov_len < tcon->ses->server->vals->read_rsp_size) {
+		/* check that the received response can hold a whole READ_RSP */
+		cifs_dbg(FYI, "%s: server returned short header. got=%zu expected=%zu\n",
+			 __func__, rsp_iov.iov_len,
+			 tcon->ses->server->vals->read_rsp_size);
+		rc = smb_EIO2(smb_eio_trace_read_rsp_short,
+			      rsp_iov.iov_len, tcon->ses->server->vals->read_rsp_size);
+		*nbytes = 0;
 	} else {
 		int data_length = le16_to_cpu(pSMBr->DataLengthHigh);
 		data_length = data_length << 16;
-- 
2.39.5