ksmbd: fix out-of-bound read in smb2_write

ksmbd_smb2_check_message doesn't validate hdr->NextCommand. If
->NextCommand is bigger than Offset + Length of smb2 write, It will
allow oversized smb2 write length. It will cause OOB read in smb2_write.

Cc: stable@vger.kernel.org
Reported-by: zdi-disclosures@trendmicro.com # ZDI-CAN-21164
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>

diff --git a/fs/smb/server/smb2misc.c b/fs/smb/server/smb2misc.c
index 57749f4..33b7e6c 100644 (file)
--- a/fs/smb/server/smb2misc.c
+++ b/fs/smb/server/smb2misc.c
@@ -351,10 +351,16 @@ int ksmbd_smb2_check_message(struct ksmbd_work *work)
        int command;
        __u32 clc_len;  /* calculated length */
        __u32 len = get_rfc1002_len(work->request_buf);
-       __u32 req_struct_size;
+       __u32 req_struct_size, next_cmd = le32_to_cpu(hdr->NextCommand);
 
-       if (le32_to_cpu(hdr->NextCommand) > 0)
-               len = le32_to_cpu(hdr->NextCommand);
+       if ((u64)work->next_smb2_rcv_hdr_off + next_cmd > len) {
+               pr_err("next command(%u) offset exceeds smb msg size\n",
+                               next_cmd);
+               return 1;
+       }
+
+       if (next_cmd > 0)
+               len = next_cmd;
        else if (work->next_smb2_rcv_hdr_off)
                len -= work->next_smb2_rcv_hdr_off;