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authorKees Cook <keescook@chromium.org>2012-03-19 16:12:53 -0700
committerThomas Gleixner <tglx@linutronix.de>2012-03-29 11:37:17 +0200
commitbdbb776f882f5ad431aa1e694c69c1c3d6a4a5b8 (patch)
tree854b6b5869857d40a02d21bb51b375812bdb2ed0 /kernel/futex_compat.c
parentb5174fa3a7f4f8f150bfa3b917c92608953dfa0f (diff)
downloadlinaro-lsk-bdbb776f882f5ad431aa1e694c69c1c3d6a4a5b8.tar.gz
futex: Do not leak robust list to unprivileged process
It was possible to extract the robust list head address from a setuid process if it had used set_robust_list(), allowing an ASLR info leak. This changes the permission checks to be the same as those used for similar info that comes out of /proc. Running a setuid program that uses robust futexes would have had: cred->euid != pcred->euid cred->euid == pcred->uid so the old permissions check would allow it. I'm not aware of any setuid programs that use robust futexes, so this is just a preventative measure. (This patch is based on changes from grsecurity.) Signed-off-by: Kees Cook <keescook@chromium.org> Cc: Darren Hart <dvhart@linux.intel.com> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Jiri Kosina <jkosina@suse.cz> Cc: Eric W. Biederman <ebiederm@xmission.com> Cc: David Howells <dhowells@redhat.com> Cc: Serge E. Hallyn <serge.hallyn@canonical.com> Cc: kernel-hardening@lists.openwall.com Cc: spender@grsecurity.net Link: http://lkml.kernel.org/r/20120319231253.GA20893@www.outflux.net Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Diffstat (limited to 'kernel/futex_compat.c')
-rw-r--r--kernel/futex_compat.c36
1 files changed, 13 insertions, 23 deletions
diff --git a/kernel/futex_compat.c b/kernel/futex_compat.c
index 5f9e689dc8f..a9642d52863 100644
--- a/kernel/futex_compat.c
+++ b/kernel/futex_compat.c
@@ -10,6 +10,7 @@
#include <linux/compat.h>
#include <linux/nsproxy.h>
#include <linux/futex.h>
+#include <linux/ptrace.h>
#include <asm/uaccess.h>
@@ -136,40 +137,29 @@ compat_sys_get_robust_list(int pid, compat_uptr_t __user *head_ptr,
{
struct compat_robust_list_head __user *head;
unsigned long ret;
- const struct cred *cred = current_cred(), *pcred;
+ struct task_struct *p;
if (!futex_cmpxchg_enabled)
return -ENOSYS;
+ rcu_read_lock();
+
+ ret = -ESRCH;
if (!pid)
- head = current->compat_robust_list;
+ p = current;
else {
- struct task_struct *p;
-
- ret = -ESRCH;
- rcu_read_lock();
p = find_task_by_vpid(pid);
if (!p)
goto err_unlock;
- ret = -EPERM;
- pcred = __task_cred(p);
- /* If victim is in different user_ns, then uids are not
- comparable, so we must have CAP_SYS_PTRACE */
- if (cred->user->user_ns != pcred->user->user_ns) {
- if (!ns_capable(pcred->user->user_ns, CAP_SYS_PTRACE))
- goto err_unlock;
- goto ok;
- }
- /* If victim is in same user_ns, then uids are comparable */
- if (cred->euid != pcred->euid &&
- cred->euid != pcred->uid &&
- !ns_capable(pcred->user->user_ns, CAP_SYS_PTRACE))
- goto err_unlock;
-ok:
- head = p->compat_robust_list;
- rcu_read_unlock();
}
+ ret = -EPERM;
+ if (!ptrace_may_access(p, PTRACE_MODE_READ))
+ goto err_unlock;
+
+ head = p->compat_robust_list;
+ rcu_read_unlock();
+
if (put_user(sizeof(*head), len_ptr))
return -EFAULT;
return put_user(ptr_to_compat(head), head_ptr);