cifs: fix rename() by ensuring source handle opened with DELETE bit

To rename a file in SMB2 we open it with the DELETE access and do a
special SetInfo on it. If the handle is missing the DELETE bit the
server will fail the SetInfo with STATUS_ACCESS_DENIED.

We currently try to reuse any existing opened handle we have with
cifs_get_writable_path(). That function looks for handles with WRITE
access but doesn't check for DELETE, making rename() fail if it finds
a handle to reuse. Simple reproducer below.

To select handles with the DELETE bit, this patch adds a flag argument
to cifs_get_writable_path() and find_writable_file() and the existing
'bool fsuid_only' argument is converted to a flag.

The cifsFileInfo struct only stores the UNIX open mode but not the
original SMB access flags. Since the DELETE bit is not mapped in that
mode, this patch stores the access mask in cifs_fid on file open,
which is accessible from cifsFileInfo.

Simple reproducer:

	#include <stdio.h>
	#include <stdlib.h>
	#include <sys/types.h>
	#include <sys/stat.h>
	#include <fcntl.h>
	#include <unistd.h>
	#define E(s) perror(s), exit(1)

	int main(int argc, char *argv[])
	{
		int fd, ret;
		if (argc != 3) {
			fprintf(stderr, "Usage: %s A B\n"
			"create&open A in write mode, "
			"rename A to B, close A\n", argv[0]);
			return 0;
		}

		fd = openat(AT_FDCWD, argv[1], O_WRONLY|O_CREAT|O_SYNC, 0666);
		if (fd == -1) E("openat()");

		ret = rename(argv[1], argv[2]);
		if (ret) E("rename()");

		ret = close(fd);
		if (ret) E("close()");

		return ret;
	}

$ gcc -o bugrename bugrename.c
$ ./bugrename /mnt/a /mnt/b
rename(): Permission denied

Fixes: 8de9e86c67ba ("cifs: create a helper to find a writeable handle by path name")
CC: Stable <stable@vger.kernel.org>
Signed-off-by: Aurelien Aptel <aaptel@suse.com>
Signed-off-by: Steve French <stfrench@microsoft.com>
Reviewed-by: Pavel Shilovsky <pshilov@microsoft.com>
Reviewed-by: Paulo Alcantara (SUSE) <pc@cjr.nz>

1 files changed, 1 insertions, 0 deletions

diff --git a/fs/cifs/smb2pdu.c b/fs/cifs/smb2pdu.c
index 1234f9ccab03..28c0be5e69b7 100644
--- a/fs/cifs/smb2pdu.c
+++ b/fs/cifs/smb2pdu.c
@@ -2771,6 +2771,7 @@ SMB2_open(const unsigned int xid, struct cifs_open_parms *oparms, __le16 *path,
 	atomic_inc(&tcon->num_remote_opens);
 	oparms->fid->persistent_fid = rsp->PersistentFileId;
 	oparms->fid->volatile_fid = rsp->VolatileFileId;
+	oparms->fid->access = oparms->desired_access;
 #ifdef CONFIG_CIFS_DEBUG2
 	oparms->fid->mid = le64_to_cpu(rsp->sync_hdr.MessageId);
 #endif /* CIFS_DEBUG2 */