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Subject[PATCH] fanotify: Make sure to check event_len when copying
As a precaution, make sure we check event_len when copying to userspace.
Based on old feedback: https://lkml.kernel.org/r/542D9FE5.3010009@gmx.de

Signed-off-by: Kees Cook <keescook@chromium.org>
---
fs/notify/fanotify/fanotify_user.c | 10 ++++++++--
1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/fs/notify/fanotify/fanotify_user.c b/fs/notify/fanotify/fanotify_user.c
index e03be5071362..d9484a0ac6b3 100644
--- a/fs/notify/fanotify/fanotify_user.c
+++ b/fs/notify/fanotify/fanotify_user.c
@@ -206,7 +206,7 @@ static int process_access_response(struct fsnotify_group *group,

static ssize_t copy_event_to_user(struct fsnotify_group *group,
struct fsnotify_event *event,
- char __user *buf)
+ char __user *buf, size_t count)
{
struct fanotify_event_metadata fanotify_event_metadata;
struct file *f;
@@ -220,6 +220,12 @@ static ssize_t copy_event_to_user(struct fsnotify_group *group,

fd = fanotify_event_metadata.fd;
ret = -EFAULT;
+ /*
+ * Sanity check copy size in case get_one_event() and
+ * fill_event_metadata() event_len sizes ever get out of sync.
+ */
+ if (WARN_ON_ONCE(fanotify_event_metadata.event_len > count))
+ goto out_close_fd;
if (copy_to_user(buf, &fanotify_event_metadata,
fanotify_event_metadata.event_len))
goto out_close_fd;
@@ -295,7 +301,7 @@ static ssize_t fanotify_read(struct file *file, char __user *buf,
continue;
}

- ret = copy_event_to_user(group, kevent, buf);
+ ret = copy_event_to_user(group, kevent, buf, count);
if (unlikely(ret == -EOPENSTALE)) {
/*
* We cannot report events with stale fd so drop it.
--
2.17.1

--
Kees Cook

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