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, 2 insertions, 1 deletions

diff --git a/fs/cifs/smb2ops.c b/fs/cifs/smb2ops.c
index e47190cae163..c31e84ee3c39 100644
--- a/fs/cifs/smb2ops.c
+++ b/fs/cifs/smb2ops.c
@@ -1364,6 +1364,7 @@ smb2_set_fid(struct cifsFileInfo *cfile, struct cifs_fid *fid, __u32 oplock)
 
 	cfile->fid.persistent_fid = fid->persistent_fid;
 	cfile->fid.volatile_fid = fid->volatile_fid;
+	cfile->fid.access = fid->access;
 #ifdef CONFIG_CIFS_DEBUG2
 	cfile->fid.mid = fid->mid;
 #endif /* CIFS_DEBUG2 */
@@ -3327,7 +3328,7 @@ static loff_t smb3_llseek(struct file *file, struct cifs_tcon *tcon, loff_t offs
 	 * some servers (Windows2016) will not reflect recent writes in
 	 * QUERY_ALLOCATED_RANGES until SMB2_flush is called.
 	 */
-	wrcfile = find_writable_file(cifsi, false);
+	wrcfile = find_writable_file(cifsi, FIND_WR_ANY);
 	if (wrcfile) {
 		filemap_write_and_wait(inode->i_mapping);
 		smb2_flush_file(xid, tcon, &wrcfile->fid);