Messages in this thread |  | | Date | Thu, 9 Jun 2022 10:51:44 +0200 | Subject | Re: [PATCH 16/36] tty/vt: consolemap: check put_user() in con_get_unimap() | From | Jiri Slaby <> |
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On 08. 06. 22, 10:11, Jiri Slaby wrote: > On 08. 06. 22, 10:02, David Laight wrote: >> From: Jiri Slaby >>> Sent: 07 June 2022 11:49 >>> >>> Only the return value of copy_to_user() is checked in con_get_unimap(). >>> Do the same for put_user() of the count too. >>> >>> Signed-off-by: Jiri Slaby <jslaby@suse.cz> >>> --- >>> drivers/tty/vt/consolemap.c | 3 ++- >>> 1 file changed, 2 insertions(+), 1 deletion(-) >>> >>> diff --git a/drivers/tty/vt/consolemap.c b/drivers/tty/vt/consolemap.c >>> index 831450f2bfd1..92b5dddb00d9 100644 >>> --- a/drivers/tty/vt/consolemap.c >>> +++ b/drivers/tty/vt/consolemap.c >>> @@ -813,7 +813,8 @@ int con_get_unimap(struct vc_data *vc, ushort ct, >>> ushort __user *uct, >>> console_unlock(); >>> if (copy_to_user(list, unilist, min(ect, ct) * sizeof(*unilist))) >>> ret = -EFAULT; >>> - put_user(ect, uct); >>> + if (put_user(ect, uct)) >>> + ret = -EFAULT; >>> kvfree(unilist); >>> return ret ? ret : (ect <= ct) ? 0 : -ENOMEM; >>> } >> >> How is the user expected to check the result of this code? >> >> AFAICT -ENOMEM is returned if either kmalloc() fails or >> the user buffer is too short? >> Looks pretty hard to detect which. > > Agreed. The code is far from perfect. We might try to return ENOSPC and > watch what breaks.
brltty and kbd (see below) would break at least: https://sources.debian.org/src/brltty/6.4-6/Drivers/Screen/Linux/screen.c/#L875
brltty apparently relies exactly on ENOMEM, increases buffer if that error is returned, and retries.
So I don't think we can change that ENOMEM to anything else.
>> I've not looked at the effect of all the patches, but setting >> 'ret = -ENOMEM' and breaking the loop when the array is too >> small would simplify things.
That would break kbd for example: https://sources.debian.org/src/kbd/2.3.0-3/src/libkfont/kdmapop.c/?hl=154#L159
GIO_UNIMAP is called with zero count to actually find out the count...
So apart from the original patch which checks the return value of put_user, we cannot do anything else. (Except decoupling the "?:" to make it more readable.)
thanks, -- js suse labs
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