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, 12 insertions, 7 deletions

diff --git a/fs/cifs/file.c b/fs/cifs/file.c
index bc9516ab4b34..3b942ecdd4be 100644
--- a/fs/cifs/file.c
+++ b/fs/cifs/file.c
@@ -1958,7 +1958,7 @@ struct cifsFileInfo *find_readable_file(struct cifsInodeInfo *cifs_inode,
 
 /* Return -EBADF if no handle is found and general rc otherwise */
 int
-cifs_get_writable_file(struct cifsInodeInfo *cifs_inode, bool fsuid_only,
+cifs_get_writable_file(struct cifsInodeInfo *cifs_inode, int flags,
 		       struct cifsFileInfo **ret_file)
 {
 	struct cifsFileInfo *open_file, *inv_file = NULL;
@@ -1966,7 +1966,8 @@ cifs_get_writable_file(struct cifsInodeInfo *cifs_inode, bool fsuid_only,
 	bool any_available = false;
 	int rc = -EBADF;
 	unsigned int refind = 0;
-
+	bool fsuid_only = flags & FIND_WR_FSUID_ONLY;
+	bool with_delete = flags & FIND_WR_WITH_DELETE;
 	*ret_file = NULL;
 
 	/*
@@ -1998,6 +1999,8 @@ refind_writable:
 			continue;
 		if (fsuid_only && !uid_eq(open_file->uid, current_fsuid()))
 			continue;
+		if (with_delete && !(open_file->fid.access & DELETE))
+			continue;
 		if (OPEN_FMODE(open_file->f_flags) & FMODE_WRITE) {
 			if (!open_file->invalidHandle) {
 				/* found a good writable file */
@@ -2045,12 +2048,12 @@ refind_writable:
 }
 
 struct cifsFileInfo *
-find_writable_file(struct cifsInodeInfo *cifs_inode, bool fsuid_only)
+find_writable_file(struct cifsInodeInfo *cifs_inode, int flags)
 {
 	struct cifsFileInfo *cfile;
 	int rc;
 
-	rc = cifs_get_writable_file(cifs_inode, fsuid_only, &cfile);
+	rc = cifs_get_writable_file(cifs_inode, flags, &cfile);
 	if (rc)
 		cifs_dbg(FYI, "couldn't find writable handle rc=%d", rc);
 
@@ -2059,6 +2062,7 @@ find_writable_file(struct cifsInodeInfo *cifs_inode, bool fsuid_only)
 
 int
 cifs_get_writable_path(struct cifs_tcon *tcon, const char *name,
+		       int flags,
 		       struct cifsFileInfo **ret_file)
 {
 	struct list_head *tmp;
@@ -2085,7 +2089,7 @@ cifs_get_writable_path(struct cifs_tcon *tcon, const char *name,
 		kfree(full_path);
 		cinode = CIFS_I(d_inode(cfile->dentry));
 		spin_unlock(&tcon->open_file_lock);
-		return cifs_get_writable_file(cinode, 0, ret_file);
+		return cifs_get_writable_file(cinode, flags, ret_file);
 	}
 
 	spin_unlock(&tcon->open_file_lock);
@@ -2162,7 +2166,8 @@ static int cifs_partialpagewrite(struct page *page, unsigned from, unsigned to)
 	if (mapping->host->i_size - offset < (loff_t)to)
 		to = (unsigned)(mapping->host->i_size - offset);
 
-	rc = cifs_get_writable_file(CIFS_I(mapping->host), false, &open_file);
+	rc = cifs_get_writable_file(CIFS_I(mapping->host), FIND_WR_ANY,
+				    &open_file);
 	if (!rc) {
 		bytes_written = cifs_write(open_file, open_file->pid,
 					   write_data, to - from, &offset);
@@ -2355,7 +2360,7 @@ retry:
 		if (cfile)
 			cifsFileInfo_put(cfile);
 
-		rc = cifs_get_writable_file(CIFS_I(inode), false, &cfile);
+		rc = cifs_get_writable_file(CIFS_I(inode), FIND_WR_ANY, &cfile);
 
 		/* in case of an error store it to return later */
 		if (rc)