Re: [PATCH v8 1/2] seccomp: add a return code to trap to userspace
From: Kees Cook <hidden>
Date: 2018-10-30 21:38:45
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On Tue, Oct 30, 2018 at 8:54 AM, Tycho Andersen [off-list ref] wrote:
On Tue, Oct 30, 2018 at 04:02:54PM +0100, Oleg Nesterov wrote:quoted
On 10/29, Tycho Andersen wrote:quoted
+static long seccomp_notify_recv(struct seccomp_filter *filter, + void __user *buf) +{ + struct seccomp_knotif *knotif = NULL, *cur; + struct seccomp_notif unotif; + ssize_t ret; + + memset(&unotif, 0, sizeof(unotif)); + + ret = down_interruptible(&filter->notif->request); + if (ret < 0) + return ret; + + mutex_lock(&filter->notify_lock); + list_for_each_entry(cur, &filter->notif->notifications, list) { + if (cur->state == SECCOMP_NOTIFY_INIT) { + knotif = cur; + break; + } + } + + /* + * If we didn't find a notification, it could be that the task was + * interrupted by a fatal signal between the time we were woken and + * when we were able to acquire the rw lock. + * + * This is the place where we handle the extra high semaphore count + * mentioned in seccomp_do_user_notification(). + */ + if (!knotif) { + ret = -ENOENT; + goto out; + } + + unotif.id = knotif->id; + unotif.pid = task_pid_vnr(knotif->task); + if (knotif->signaled) + unotif.flags |= SECCOMP_NOTIF_FLAG_SIGNALED; + unotif.data = *(knotif->data);Tycho, I forgot everything about seccomp, most probably I am wrong but let me ask anyway. __seccomp_filter(SECCOMP_RET_TRACE) does /* * Recheck the syscall, since it may have changed. This * intentionally uses a NULL struct seccomp_data to force * a reload of all registers. This does not goto skip since * a skip would have already been reported. */ if (__seccomp_filter(this_syscall, NULL, true)) return -1; and the next seccomp_run_filters() can return SECCOMP_RET_USER_NOTIF, right? seccomp_do_user_notification() doesn't check recheck_after_trace and it simply does n.data = sd. Doesn't this mean that "unotif.data = *(knotif->data)" can hit NULL ? seccomp_run_filters() does populate_seccomp_data() in this case, but this won't affect "seccomp_data *sd" passed to seccomp_do_user_notification().
Woo, yeah, good catch. :)
Oof, yes, you're right. Seems like there are no other users of sd in __seccomp_filter(). Seems to me like we can just do the populate_seccomp_data() one level higher in __seccomp_filter()?
Agreed.
quoted hunk ↗ jump to hunk
Tycho From 9e0f75ea51a2c328567910df3122a236ebeccab0 Mon Sep 17 00:00:00 2001 From: Tycho Andersen <redacted> Date: Tue, 30 Oct 2018 09:51:14 -0600 Subject: [PATCH] seccomp: hoist struct seccomp_data recalculation higher Signed-off-by: Tycho Andersen <redacted> --- kernel/seccomp.c | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-)diff --git a/kernel/seccomp.c b/kernel/seccomp.c index 4c5fb6ced4cd..1525cb753ad2 100644 --- a/kernel/seccomp.c +++ b/kernel/seccomp.c@@ -257,7 +257,6 @@ static int seccomp_check_filter(struct sock_filter *filter, unsigned int flen) static u32 seccomp_run_filters(const struct seccomp_data *sd, struct seccomp_filter **match) { - struct seccomp_data sd_local; u32 ret = SECCOMP_RET_ALLOW; /* Make sure cross-thread synced filter points somewhere sane. */ struct seccomp_filter *f =@@ -267,11 +266,6 @@ static u32 seccomp_run_filters(const struct seccomp_data *sd, if (unlikely(WARN_ON(f == NULL))) return SECCOMP_RET_KILL_PROCESS; - if (!sd) { - populate_seccomp_data(&sd_local); - sd = &sd_local; - } - /* * All filters in the list are evaluated and the lowest BPF return * value always takes priority (ignoring the DATA).@@ -821,6 +815,7 @@ static int __seccomp_filter(int this_syscall, const struct seccomp_data *sd, u32 filter_ret, action; struct seccomp_filter *match = NULL; int data; + struct seccomp_data sd_local; /* * Make sure that any changes to mode from another thread have@@ -828,6 +823,11 @@ static int __seccomp_filter(int this_syscall, const struct seccomp_data *sd, */ rmb(); + if (!sd) { + populate_seccomp_data(&sd_local); + sd = &sd_local; + } + filter_ret = seccomp_run_filters(sd, &match); data = filter_ret & SECCOMP_RET_DATA; action = filter_ret & SECCOMP_RET_ACTION_FULL; --2.17.1
Looks good to me, yes. -- Kees Cook