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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: Richard Weinberger <richard@nod.at>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Cc: <stable@vger.kernel.org> # v3.18+
Fixes: e9be9d5e76 ("overlay filesystem")
This commit is contained in:
Richard Weinberger 2016-09-16 11:45:24 +02:00 committed by Miklos Szeredi
parent 8eac98b8be
commit 6a45b3628c
1 changed files with 4 additions and 1 deletions
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5
fs/overlayfs/dir.c
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@ -14,6 +14,7 @@
#include <linux/cred.h> #include <linux/cred.h>
#include <linux/posix_acl.h> #include <linux/posix_acl.h>
#include <linux/posix_acl_xattr.h> #include <linux/posix_acl_xattr.h>
#include <linux/atomic.h>
#include "overlayfs.h" #include "overlayfs.h"
void ovl_cleanup(struct inode *wdir, struct dentry *wdentry) 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; struct dentry *temp;
char name[20]; 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)); temp = lookup_one_len(name, workdir, strlen(name));
if (!IS_ERR(temp) && temp->d_inode) { if (!IS_ERR(temp) && temp->d_inode) {