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Commit 6a45b362 authored by Richard Weinberger's avatar Richard Weinberger Committed by Miklos Szeredi
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ovl: Fix info leak in ovl_lookup_temp() 



The function uses the memory address of a struct dentry as unique id.
While the address-based directory entry is only visible to root it is IMHO
still worth fixing since the temporary name does not have to be a kernel
address.  It can be any unique number.  Replace it by an atomic integer
which is allowed to wrap around.

Signed-off-by: default avatarRichard Weinberger <richard@nod.at>
Reviewed-by: default avatarKees Cook <keescook@chromium.org>
Signed-off-by: default avatarMiklos Szeredi <mszeredi@redhat.com>
Cc: <stable@vger.kernel.org> # v3.18+
Fixes: e9be9d5e ("overlay filesystem")
parent 8eac98b8

fs/overlayfs/dir.c

+4 −1
Original line number Diff line number Diff line
@@ -14,6 +14,7 @@ 
#include <linux/cred.h>

#include <linux/posix_acl.h>

#include <linux/posix_acl_xattr.h>

#include <linux/atomic.h>

#include "overlayfs.h"



void ovl_cleanup(struct inode *wdir, struct dentry *wdentry)
@@ -37,8 +38,10 @@ struct dentry *ovl_lookup_temp(struct dentry *workdir, struct dentry *dentry) 
{

	struct dentry *temp;

	char name[20];

	static atomic_t temp_id = ATOMIC_INIT(0);



	snprintf(name, sizeof(name), "#%lx", (unsigned long) dentry);

	/* counter is allowed to wrap, since temp dentries are ephemeral */

	snprintf(name, sizeof(name), "#%x", atomic_inc_return(&temp_id));



	temp = lookup_one_len(name, workdir, strlen(name));

	if (!IS_ERR(temp) && temp->d_inode) {