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authorTycho Andersen <tycho@tycho.pizza>2020-09-01 19:40:16 -0600
committerKees Cook <keescook@chromium.org>2020-09-08 11:19:50 -0700
commita566a9012acd7c9a4be7e30dc7acb7a811ec2260 (patch)
treeeaf1faa6cece4d4ba2d24192d6bf9cf633f47a44
parentd012a7190fc1fd72ed48911e77ca97ba4521bccd (diff)
seccomp: don't leak memory when filter install races
In seccomp_set_mode_filter() with TSYNC | NEW_LISTENER, we first initialize the listener fd, then check to see if we can actually use it later in seccomp_may_assign_mode(), which can fail if anyone else in our thread group has installed a filter and caused some divergence. If we can't, we partially clean up the newly allocated file: we put the fd, put the file, but don't actually clean up the *memory* that was allocated at filter->notif. Let's clean that up too. To accomplish this, let's hoist the actual "detach a notifier from a filter" code to its own helper out of seccomp_notify_release(), so that in case anyone adds stuff to init_listener(), they only have to add the cleanup code in one spot. This does a bit of extra locking and such on the failure path when the filter is not attached, but it's a slow failure path anyway. Fixes: 51891498f2da ("seccomp: allow TSYNC and USER_NOTIF together") Reported-by: syzbot+3ad9614a12f80994c32e@syzkaller.appspotmail.com Signed-off-by: Tycho Andersen <tycho@tycho.pizza> Acked-by: Christian Brauner <christian.brauner@ubuntu.com> Link: https://lore.kernel.org/r/20200902014017.934315-1-tycho@tycho.pizza Signed-off-by: Kees Cook <keescook@chromium.org>
-rw-r--r--kernel/seccomp.c13
1 files changed, 10 insertions, 3 deletions
diff --git a/kernel/seccomp.c b/kernel/seccomp.c
index 3ee59ce0a323..bb0dd9ae699a 100644
--- a/kernel/seccomp.c
+++ b/kernel/seccomp.c
@@ -1109,13 +1109,12 @@ out:
}
#ifdef CONFIG_SECCOMP_FILTER
-static int seccomp_notify_release(struct inode *inode, struct file *file)
+static void seccomp_notify_detach(struct seccomp_filter *filter)
{
- struct seccomp_filter *filter = file->private_data;
struct seccomp_knotif *knotif;
if (!filter)
- return 0;
+ return;
mutex_lock(&filter->notify_lock);
@@ -1142,6 +1141,13 @@ static int seccomp_notify_release(struct inode *inode, struct file *file)
kfree(filter->notif);
filter->notif = NULL;
mutex_unlock(&filter->notify_lock);
+}
+
+static int seccomp_notify_release(struct inode *inode, struct file *file)
+{
+ struct seccomp_filter *filter = file->private_data;
+
+ seccomp_notify_detach(filter);
__put_seccomp_filter(filter);
return 0;
}
@@ -1581,6 +1587,7 @@ out_put_fd:
listener_f->private_data = NULL;
fput(listener_f);
put_unused_fd(listener);
+ seccomp_notify_detach(prepared);
} else {
fd_install(listener, listener_f);
ret = listener;