From bdbb776f882f5ad431aa1e694c69c1c3d6a4a5b8 Mon Sep 17 00:00:00 2001 From: Kees Cook Date: Mon, 19 Mar 2012 16:12:53 -0700 Subject: [PATCH] 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 Cc: Darren Hart Cc: Peter Zijlstra Cc: Jiri Kosina Cc: Eric W. Biederman Cc: David Howells Cc: Serge E. Hallyn 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 --- kernel/futex.c | 38 ++++++++++++++------------------------ kernel/futex_compat.c | 38 ++++++++++++++------------------------ 2 files changed, 28 insertions(+), 48 deletions(-) diff --git a/kernel/futex.c b/kernel/futex.c index 72efa1e4359a..d701be57c423 100644 --- a/kernel/futex.c +++ b/kernel/futex.c @@ -59,6 +59,7 @@ #include #include #include +#include #include @@ -2443,40 +2444,29 @@ SYSCALL_DEFINE3(get_robust_list, int, pid, { struct 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; - if (!pid) - head = current->robust_list; - else { - struct task_struct *p; + rcu_read_lock(); - ret = -ESRCH; - rcu_read_lock(); + ret = -ESRCH; + if (!pid) + p = current; + else { 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->robust_list; - rcu_read_unlock(); } + ret = -EPERM; + if (!ptrace_may_access(p, PTRACE_MODE_READ)) + goto err_unlock; + + head = p->robust_list; + rcu_read_unlock(); + if (put_user(sizeof(*head), len_ptr)) return -EFAULT; return put_user(head, head_ptr); diff --git a/kernel/futex_compat.c b/kernel/futex_compat.c index 5f9e689dc8f0..a9642d528630 100644 --- a/kernel/futex_compat.c +++ b/kernel/futex_compat.c @@ -10,6 +10,7 @@ #include #include #include +#include #include @@ -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; - if (!pid) - head = current->compat_robust_list; - else { - struct task_struct *p; + rcu_read_lock(); - ret = -ESRCH; - rcu_read_lock(); + ret = -ESRCH; + if (!pid) + p = current; + else { 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);