cifs: do not allow creating sockets except with SMB1 posix exensions

[ Upstream commit 1d0cffa674cfa7d185a302c8c6850fc50b893bed ]

RHBZ: 1453123

Since at least the 3.10 kernel and likely a lot earlier we have
not been able to create unix domain sockets in a cifs share
when mounted using the SFU mount option (except when mounted
with the cifs unix extensions to Samba e.g.)
Trying to create a socket, for example using the af_unix command from
xfstests will cause :
BUG: unable to handle kernel NULL pointer dereference at 00000000
00000040

Since no one uses or depends on being able to create unix domains sockets
on a cifs share the easiest fix to stop this vulnerability is to simply
not allow creation of any other special files than char or block devices
when sfu is used.

Added update to Ronnie's patch to handle a tcon link leak, and
to address a buf leak noticed by Gustavo and Colin.

Acked-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
CC:  Colin Ian King <colin.king@canonical.com>
Reviewed-by: Pavel Shilovsky <pshilov@microsoft.com>
Reported-by: Eryu Guan <eguan@redhat.com>
Signed-off-by: Ronnie Sahlberg <lsahlber@redhat.com>
Signed-off-by: Steve French <smfrench@gmail.com>
Cc: stable@vger.kernel.org
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>

diff --git a/fs/cifs/dir.c b/fs/cifs/dir.c
index 49a0d6b027c19d0a3cf8967d7aa40a3b023109b0..76dacd5307b9a93ad43afb61e09a5d9a43cb4cb2 100644 (file)
--- a/fs/cifs/dir.c
+++ b/fs/cifs/dir.c
@@ -673,6 +673,9 @@ int cifs_mknod(struct inode *inode, struct dentry *direntry, umode_t mode,
                goto mknod_out;
        }
 
+       if (!S_ISCHR(mode) && !S_ISBLK(mode))
+               goto mknod_out;
+
        if (!(cifs_sb->mnt_cifs_flags & CIFS_MOUNT_UNX_EMUL))
                goto mknod_out;
 
@@ -681,10 +684,8 @@ int cifs_mknod(struct inode *inode, struct dentry *direntry, umode_t mode,
 
        buf = kmalloc(sizeof(FILE_ALL_INFO), GFP_KERNEL);
        if (buf == NULL) {
-               kfree(full_path);
                rc = -ENOMEM;
-               free_xid(xid);
-               return rc;
+               goto mknod_out;
        }
 
        if (backup_cred(cifs_sb))
@@ -731,7 +732,7 @@ int cifs_mknod(struct inode *inode, struct dentry *direntry, umode_t mode,
                pdev->minor = cpu_to_le64(MINOR(device_number));
                rc = tcon->ses->server->ops->sync_write(xid, &fid, &io_parms,
                                                        &bytes_written, iov, 1);
-       } /* else if (S_ISFIFO) */
+       }
        tcon->ses->server->ops->close(xid, tcon, &fid);
        d_drop(direntry);