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author | Kees Cook <keescook@chromium.org> | 2012-03-20 00:12:53 +0100 |
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committer | Thomas Gleixner <tglx@linutronix.de> | 2012-03-29 11:37:17 +0200 |
commit | bdbb776f882f5ad431aa1e694c69c1c3d6a4a5b8 (patch) | |
tree | 854b6b5869857d40a02d21bb51b375812bdb2ed0 /kernel/futex_compat.c | |
parent | Merge tag 'mmc-merge-for-3.4-rc1' of git://git.kernel.org/pub/scm/linux/kerne... (diff) | |
download | linux-bdbb776f882f5ad431aa1e694c69c1c3d6a4a5b8.tar.xz linux-bdbb776f882f5ad431aa1e694c69c1c3d6a4a5b8.zip |
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.c | 36 |
1 files changed, 13 insertions, 23 deletions
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 <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); |