From b2d22b6bb33aac10c415e4ba13c8eade201c6f09 Mon Sep 17 00:00:00 2001 From: Jan Kara Date: Tue, 12 Mar 2019 12:42:37 +0100 Subject: fanotify: Allow copying of file handle to userspace When file handle is embedded inside fanotify_event and usercopy checks are enabled, we get a warning like: Bad or missing usercopy whitelist? Kernel memory exposure attempt detected from SLAB object 'fanotify_event' (offset 40, size 8)! WARNING: CPU: 1 PID: 7649 at mm/usercopy.c:78 usercopy_warn+0xeb/0x110 mm/usercopy.c:78 Annotate handling in fanotify_event properly to mark copying it to userspace is fine. Reported-by: syzbot+2c49971e251e36216d1f@syzkaller.appspotmail.com Fixes: a8b13aa20afb ("fanotify: enable FAN_REPORT_FID init flag") Signed-off-by: Kees Cook Reviewed-by: Amir Goldstein Signed-off-by: Jan Kara --- fs/notify/fanotify/fanotify_user.c | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-) (limited to 'fs/notify') diff --git a/fs/notify/fanotify/fanotify_user.c b/fs/notify/fanotify/fanotify_user.c index 56992b32c6bb..a90bb19dcfa2 100644 --- a/fs/notify/fanotify/fanotify_user.c +++ b/fs/notify/fanotify/fanotify_user.c @@ -208,6 +208,7 @@ static int copy_fid_to_user(struct fanotify_event *event, char __user *buf) { struct fanotify_event_info_fid info = { }; struct file_handle handle = { }; + unsigned char bounce[FANOTIFY_INLINE_FH_LEN], *fh; size_t fh_len = event->fh_len; size_t len = fanotify_event_info_len(event); @@ -233,7 +234,16 @@ static int copy_fid_to_user(struct fanotify_event *event, char __user *buf) buf += sizeof(handle); len -= sizeof(handle); - if (copy_to_user(buf, fanotify_event_fh(event), fh_len)) + /* + * For an inline fh, copy through stack to exclude the copy from + * usercopy hardening protections. + */ + fh = fanotify_event_fh(event); + if (fh_len <= FANOTIFY_INLINE_FH_LEN) { + memcpy(bounce, fh, fh_len); + fh = bounce; + } + if (copy_to_user(buf, fh, fh_len)) return -EFAULT; /* Pad with 0's */ -- cgit v1.2.3