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Message-Id: <3386f680206b9ce91974dd49bbeea1e24bf4ffcc.1460380917.git.jslaby@suse.cz>
Date: Mon, 11 Apr 2016 15:23:24 +0200
From: Jiri Slaby <jslaby@...e.cz>
To: stable@...r.kernel.org
Cc: linux-kernel@...r.kernel.org, Jann Horn <jann@...jh.net>,
Al Viro <viro@...iv.linux.org.uk>,
"Eric W. Biederman" <ebiederm@...ssion.com>,
Andy Lutomirski <luto@...nel.org>,
Oleg Nesterov <oleg@...hat.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Jiri Slaby <jslaby@...e.cz>
Subject: [PATCH 3.12 82/98] fs/coredump: prevent fsuid=0 dumps into user-controlled directories
From: Jann Horn <jann@...jh.net>
3.12-stable review patch. If anyone has any objections, please let me know.
===============
commit 378c6520e7d29280f400ef2ceaf155c86f05a71a upstream.
This commit fixes the following security hole affecting systems where
all of the following conditions are fulfilled:
- The fs.suid_dumpable sysctl is set to 2.
- The kernel.core_pattern sysctl's value starts with "/". (Systems
where kernel.core_pattern starts with "|/" are not affected.)
- Unprivileged user namespace creation is permitted. (This is
true on Linux >=3.8, but some distributions disallow it by
default using a distro patch.)
Under these conditions, if a program executes under secure exec rules,
causing it to run with the SUID_DUMP_ROOT flag, then unshares its user
namespace, changes its root directory and crashes, the coredump will be
written using fsuid=0 and a path derived from kernel.core_pattern - but
this path is interpreted relative to the root directory of the process,
allowing the attacker to control where a coredump will be written with
root privileges.
To fix the security issue, always interpret core_pattern for dumps that
are written under SUID_DUMP_ROOT relative to the root directory of init.
Signed-off-by: Jann Horn <jann@...jh.net>
Acked-by: Kees Cook <keescook@...omium.org>
Cc: Al Viro <viro@...iv.linux.org.uk>
Cc: "Eric W. Biederman" <ebiederm@...ssion.com>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Oleg Nesterov <oleg@...hat.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Jiri Slaby <jslaby@...e.cz>
---
arch/um/drivers/mconsole_kern.c | 2 +-
fs/coredump.c | 30 ++++++++++++++++++++++++++----
fs/fhandle.c | 2 +-
fs/open.c | 6 ++----
include/linux/fs.h | 2 +-
kernel/sysctl_binary.c | 2 +-
6 files changed, 32 insertions(+), 12 deletions(-)
diff --git a/arch/um/drivers/mconsole_kern.c b/arch/um/drivers/mconsole_kern.c
index 3df3bd544492..1768d4083f74 100644
--- a/arch/um/drivers/mconsole_kern.c
+++ b/arch/um/drivers/mconsole_kern.c
@@ -133,7 +133,7 @@ void mconsole_proc(struct mc_request *req)
ptr += strlen("proc");
ptr = skip_spaces(ptr);
- file = file_open_root(mnt->mnt_root, mnt, ptr, O_RDONLY);
+ file = file_open_root(mnt->mnt_root, mnt, ptr, O_RDONLY, 0);
if (IS_ERR(file)) {
mconsole_reply(req, "Failed to open file", 1, 0);
printk(KERN_ERR "open /proc/%s: %ld\n", ptr, PTR_ERR(file));
diff --git a/fs/coredump.c b/fs/coredump.c
index ff78d9075316..86753db01f2d 100644
--- a/fs/coredump.c
+++ b/fs/coredump.c
@@ -32,6 +32,9 @@
#include <linux/pipe_fs_i.h>
#include <linux/oom.h>
#include <linux/compat.h>
+#include <linux/sched.h>
+#include <linux/fs.h>
+#include <linux/path.h>
#include <asm/uaccess.h>
#include <asm/mmu_context.h>
@@ -614,6 +617,8 @@ void do_coredump(siginfo_t *siginfo)
}
} else {
struct inode *inode;
+ int open_flags = O_CREAT | O_RDWR | O_NOFOLLOW |
+ O_LARGEFILE | O_EXCL;
if (cprm.limit < binfmt->min_coredump)
goto fail_unlock;
@@ -652,10 +657,27 @@ void do_coredump(siginfo_t *siginfo)
* what matters is that at least one of the two processes
* writes its coredump successfully, not which one.
*/
- cprm.file = filp_open(cn.corename,
- O_CREAT | 2 | O_NOFOLLOW |
- O_LARGEFILE | O_EXCL,
- 0600);
+ if (need_suid_safe) {
+ /*
+ * Using user namespaces, normal user tasks can change
+ * their current->fs->root to point to arbitrary
+ * directories. Since the intention of the "only dump
+ * with a fully qualified path" rule is to control where
+ * coredumps may be placed using root privileges,
+ * current->fs->root must not be used. Instead, use the
+ * root directory of init_task.
+ */
+ struct path root;
+
+ task_lock(&init_task);
+ get_fs_root(init_task.fs, &root);
+ task_unlock(&init_task);
+ cprm.file = file_open_root(root.dentry, root.mnt,
+ cn.corename, open_flags, 0600);
+ path_put(&root);
+ } else {
+ cprm.file = filp_open(cn.corename, open_flags, 0600);
+ }
if (IS_ERR(cprm.file))
goto fail_unlock;
diff --git a/fs/fhandle.c b/fs/fhandle.c
index d59712dfa3e7..ca3c3dd01789 100644
--- a/fs/fhandle.c
+++ b/fs/fhandle.c
@@ -228,7 +228,7 @@ long do_handle_open(int mountdirfd,
path_put(&path);
return fd;
}
- file = file_open_root(path.dentry, path.mnt, "", open_flag);
+ file = file_open_root(path.dentry, path.mnt, "", open_flag, 0);
if (IS_ERR(file)) {
put_unused_fd(fd);
retval = PTR_ERR(file);
diff --git a/fs/open.c b/fs/open.c
index fc9c0ceed464..3827b632d713 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -923,14 +923,12 @@ struct file *filp_open(const char *filename, int flags, umode_t mode)
EXPORT_SYMBOL(filp_open);
struct file *file_open_root(struct dentry *dentry, struct vfsmount *mnt,
- const char *filename, int flags)
+ const char *filename, int flags, umode_t mode)
{
struct open_flags op;
- int err = build_open_flags(flags, 0, &op);
+ int err = build_open_flags(flags, mode, &op);
if (err)
return ERR_PTR(err);
- if (flags & O_CREAT)
- return ERR_PTR(-EINVAL);
if (!filename && (flags & O_DIRECTORY))
if (!dentry->d_inode->i_op->lookup)
return ERR_PTR(-ENOTDIR);
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 042b61b7a2ad..1d106873e7ba 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2005,7 +2005,7 @@ extern long do_sys_open(int dfd, const char __user *filename, int flags,
extern struct file *file_open_name(struct filename *, int, umode_t);
extern struct file *filp_open(const char *, int, umode_t);
extern struct file *file_open_root(struct dentry *, struct vfsmount *,
- const char *, int);
+ const char *, int, umode_t);
extern struct file * dentry_open(const struct path *, int, const struct cred *);
extern int filp_close(struct file *, fl_owner_t id);
diff --git a/kernel/sysctl_binary.c b/kernel/sysctl_binary.c
index b609213ca9a2..7f95a544abab 100644
--- a/kernel/sysctl_binary.c
+++ b/kernel/sysctl_binary.c
@@ -1320,7 +1320,7 @@ static ssize_t binary_sysctl(const int *name, int nlen,
}
mnt = task_active_pid_ns(current)->proc_mnt;
- file = file_open_root(mnt->mnt_root, mnt, pathname, flags);
+ file = file_open_root(mnt->mnt_root, mnt, pathname, flags, 0);
result = PTR_ERR(file);
if (IS_ERR(file))
goto out_putname;
--
2.8.1
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