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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: a8b13aa20a ("fanotify: enable FAN_REPORT_FID init flag")
Signed-off-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>
This commit is contained in:
Jan Kara 2019-03-12 12:42:37 +01:00
parent 62c9d2674b
commit b2d22b6bb3
1 changed files with 11 additions and 1 deletions
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12
fs/notify/fanotify/fanotify_user.c
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@ -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 */