[4.2.y-ckt stable] Patch "fs/coredump: prevent fsuid=0 dumps into user-controlled directories" has been added to the 4.2.y-ckt tree
Kamal Mostafa
kamal at canonical.com
Wed Mar 30 23:53:27 UTC 2016
This is a note to let you know that I have just added a patch titled
fs/coredump: prevent fsuid=0 dumps into user-controlled directories
to the linux-4.2.y-queue branch of the 4.2.y-ckt extended stable tree
which can be found at:
http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-4.2.y-queue
This patch is scheduled to be released in version 4.2.8-ckt7.
If you, or anyone else, feels it should not be added to this tree, please
reply to this email.
For more information about the 4.2.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable
Thanks.
-Kamal
---8<------------------------------------------------------------
>From 261b0a8066a222c9e65ff8341fbe2d8510361e92 Mon Sep 17 00:00:00 2001
From: Jann Horn <jann at thejh.net>
Date: Tue, 22 Mar 2016 14:25:36 -0700
Subject: fs/coredump: prevent fsuid=0 dumps into user-controlled directories
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 at thejh.net>
Acked-by: Kees Cook <keescook at chromium.org>
Cc: Al Viro <viro at zeniv.linux.org.uk>
Cc: "Eric W. Biederman" <ebiederm at xmission.com>
Cc: Andy Lutomirski <luto at kernel.org>
Cc: Oleg Nesterov <oleg at redhat.com>
Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
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 29880c9..e22e572 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 a8f7564..df6a1af 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>
@@ -628,6 +631,8 @@ void do_coredump(const 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;
@@ -666,10 +671,27 @@ void do_coredump(const 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 d59712d..ca3c3dd 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 e33dab2..50958c2 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -995,14 +995,12 @@ 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);
return do_file_open_root(dentry, mnt, filename, &op);
}
EXPORT_SYMBOL(file_open_root);
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 84b783f..5f59f86 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2222,7 +2222,7 @@ 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 7e7746a..10a1d7d 100644
--- a/kernel/sysctl_binary.c
+++ b/kernel/sysctl_binary.c
@@ -1321,7 +1321,7 @@ 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;
--
2.7.4
More information about the kernel-team
mailing list