On 29.09.2014 01:35, Kees Cook wrote:
When building with CONFIG_DEBUG_STRICT_USER_COPY_CHECKS, this copy_to_user
wasn't provably correct (the length was in a variable but the structure
wasn't). The compiler wasn't able to check that the length was being
statically assigned, so include a BUG_ON to notice if this ever changes.
Signed-off-by: Kees Cook <[email protected]>
---
fs/notify/fanotify/fanotify_user.c | 1 +
1 file changed, 1 insertion(+)
diff --git a/fs/notify/fanotify/fanotify_user.c
b/fs/notify/fanotify/fanotify_user.c
index b13992a41bd9..7bdb43222875 100644
--- a/fs/notify/fanotify/fanotify_user.c
+++ b/fs/notify/fanotify/fanotify_user.c
@@ -216,6 +216,7 @@ static ssize_t copy_event_to_user(struct fsnotify_group
*group,
fd = fanotify_event_metadata.fd;
ret = -EFAULT;
+ BUG_ON(fanotify_event_metadata.event_len != FAN_EVENT_METADATA_LEN);
Thank you for indicating an inconsistency in fanotify_user.c
In fanotify_user.c a mismatch exists between the assumptions made in
get_one_event() and copy_event_to_user().
According to the fanotify.7 man page:
"FAN_EVENT_METADATA_LEN - This is the minimum size (and currently the
only size) of any event metadata."
get_one_event() assumes that the event metadata has a length of
FAN_EVENT_METADATA_LEN and does not care about the value of event_len.
copy_event_to_user() assumes that event_len specifies the length of the
event metadata and does not care about FAN_EVENT_METADATA_LEN.
Due to these different assumptions it cannot be proven inside
fanotify_user.c that copy_to_user() is called correctly.
If we want such a prove inside fanotify_user.c, we should change
get_one_event() to use the following:
// Get the event without removing it from the group.
fsnotify_event *evt = fsnotify_peek_notify_event(group);
// Check we have enough user memory to copy the event.
if (evt->event_len > count)
return ERR_PTR(-EINVAL);
// Remove the event from the group.
fsnotify_remove_notify_event(group);
// Return the pointer we tested.
// fanotify_remove_notify_event() should return the same pointer.
return evt;
If after this change you still want a BUG_ON, pass count to
copy_event_to_user() and write
BUG_ON(fanotify_event_metadata.event_len > count);
Best regards
Heinrich Schuchardt
if (copy_to_user(buf, &fanotify_event_metadata,
fanotify_event_metadata.event_len))
goto out_close_fd;
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
