shmem: fix nlink for rename overwrite directory

If overwriting an empty directory with rename, then need to drop the extra
nlink.

Test prog:

#include <stdio.h>
#include <fcntl.h>
#include <err.h>
#include <sys/stat.h>

int main(void)
{
	const char *test_dir1 = "test-dir1";
	const char *test_dir2 = "test-dir2";
	int res;
	int fd;
	struct stat statbuf;

	res = mkdir(test_dir1, 0777);
	if (res == -1)
		err(1, "mkdir(\"%s\")", test_dir1);

	res = mkdir(test_dir2, 0777);
	if (res == -1)
		err(1, "mkdir(\"%s\")", test_dir2);

	fd = open(test_dir2, O_RDONLY);
	if (fd == -1)
		err(1, "open(\"%s\")", test_dir2);

	res = rename(test_dir1, test_dir2);
	if (res == -1)
		err(1, "rename(\"%s\", \"%s\")", test_dir1, test_dir2);

	res = fstat(fd, &statbuf);
	if (res == -1)
		err(1, "fstat(%i)", fd);

	if (statbuf.st_nlink != 0) {
		fprintf(stderr, "nlink is %lu, should be 0\n", statbuf.st_nlink);
		return 1;
	}

	return 0;
}

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Cc: stable@vger.kernel.org
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 3 insertions, 1 deletions

diff --git a/mm/shmem.c b/mm/shmem.c
index 0e5fb225007c..469f90d56051 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -2367,8 +2367,10 @@ static int shmem_rename2(struct inode *old_dir, struct dentry *old_dentry, struc
 
         if (new_dentry->d_inode) {
                 (void) shmem_unlink(new_dir, new_dentry);
-                if (they_are_dirs)
+                if (they_are_dirs) {
+                        drop_nlink(new_dentry->d_inode);
                         drop_nlink(old_dir);
+                }
         } else if (they_are_dirs) {
                 drop_nlink(old_dir);
                 inc_nlink(new_dir);