Commit 406c706c authored by Peter Griffin's avatar Peter Griffin Committed by Al Viro
Browse files

vfs: vfs_tmpfile: ensure O_EXCL flag is enforced 

If O_EXCL is *not* specified, then linkat() can be
used to link the temporary file into the filesystem.
If O_EXCL is specified then linkat() should fail (-1).

After commit 863f144f ("vfs: open inside ->tmpfile()")
the O_EXCL flag is no longer honored by the vfs layer for
tmpfile, which means the file can be linked even if O_EXCL
flag is specified, which is a change in behaviour for
userspace!

The open flags was previously passed as a parameter, so it
was uneffected by the changes to file->f_flags caused by
finish_open(). This patch fixes the issue by storing
file->f_flags in a local variable so the O_EXCL test
logic is restored.

This regression was detected by Android CTS Bionic fcntl()
tests running on android-mainline [1].

[1] https://android.googlesource.com/platform/bionic/+/


    refs/heads/master/tests/fcntl_test.cpp#352

Fixes: 863f144f ("vfs: open inside ->tmpfile()")
Acked-by: default avatarMiklos Szeredi <mszeredi@redhat.com>
Tested-by: default avatarWill McVicker <willmcvicker@google.com>
Signed-off-by: default avatarPeter Griffin <peter.griffin@linaro.org>
Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent 7ee47dcf

fs/namei.c

+2 −1
Original line number Diff line number Diff line
@@ -3591,6 +3591,7 @@ static int vfs_tmpfile(struct user_namespace *mnt_userns, 
	struct inode *dir = d_inode(parentpath->dentry);

	struct inode *inode;

	int error;

	int open_flag = file->f_flags;



	/* we want directory to be writable */

	error = inode_permission(mnt_userns, dir, MAY_WRITE | MAY_EXEC);
@@ -3613,7 +3614,7 @@ static int vfs_tmpfile(struct user_namespace *mnt_userns, 
	if (error)

		return error;

	inode = file_inode(file);

	if (!(file->f_flags & O_EXCL)) {

	if (!(open_flag & O_EXCL)) {

		spin_lock(&inode->i_lock);

		inode->i_state |= I_LINKABLE;

		spin_unlock(&inode->i_lock);