cifs: make sure we do not overflow the max EA buffer size

RHBZ: 1752437

Before we add a new EA we should check that this will not overflow
the maximum buffer we have available to read the EAs back.
Otherwise we can get into a situation where the EAs are so big that
we can not read them back to the client and thus we can not list EAs
anymore or delete them.

Signed-off-by: Ronnie Sahlberg <lsahlber@redhat.com>
Signed-off-by: Steve French <stfrench@microsoft.com>
CC: Stable <stable@vger.kernel.org>

diff --git a/fs/cifs/smb2ops.c b/fs/cifs/smb2ops.c
index aef3363..e47190c 100644 (file)
--- a/fs/cifs/smb2ops.c
+++ b/fs/cifs/smb2ops.c
@@ -1116,7 +1116,8 @@ smb2_set_ea(const unsigned int xid, struct cifs_tcon *tcon,
        void *data[1];
        struct smb2_file_full_ea_info *ea = NULL;
        struct kvec close_iov[1];
-       int rc;
+       struct smb2_query_info_rsp *rsp;
+       int rc, used_len = 0;
 
        if (smb3_encryption_required(tcon))
                flags |= CIFS_TRANSFORM_REQ;
@@ -1139,6 +1140,38 @@ smb2_set_ea(const unsigned int xid, struct cifs_tcon *tcon,
                                                             cifs_sb);
                        if (rc == -ENODATA)
                                goto sea_exit;
+               } else {
+                       /* If we are adding a attribute we should first check
+                        * if there will be enough space available to store
+                        * the new EA. If not we should not add it since we
+                        * would not be able to even read the EAs back.
+                        */
+                       rc = smb2_query_info_compound(xid, tcon, utf16_path,
+                                     FILE_READ_EA,
+                                     FILE_FULL_EA_INFORMATION,
+                                     SMB2_O_INFO_FILE,
+                                     CIFSMaxBufSize -
+                                     MAX_SMB2_CREATE_RESPONSE_SIZE -
+                                     MAX_SMB2_CLOSE_RESPONSE_SIZE,
+                                     &rsp_iov[1], &resp_buftype[1], cifs_sb);
+                       if (rc == 0) {
+                               rsp = (struct smb2_query_info_rsp *)rsp_iov[1].iov_base;
+                               used_len = le32_to_cpu(rsp->OutputBufferLength);
+                       }
+                       free_rsp_buf(resp_buftype[1], rsp_iov[1].iov_base);
+                       resp_buftype[1] = CIFS_NO_BUFFER;
+                       memset(&rsp_iov[1], 0, sizeof(rsp_iov[1]));
+                       rc = 0;
+
+                       /* Use a fudge factor of 256 bytes in case we collide
+                        * with a different set_EAs command.
+                        */
+                       if(CIFSMaxBufSize - MAX_SMB2_CREATE_RESPONSE_SIZE -
+                          MAX_SMB2_CLOSE_RESPONSE_SIZE - 256 <
+                          used_len + ea_name_len + ea_value_len + 1) {
+                               rc = -ENOSPC;
+                               goto sea_exit;
+                       }
                }
        }