Messages in this thread | | | Date | Wed, 10 Nov 2021 06:22:21 +0100 | Subject | Re: [PATCH] tty: vt: keyboard: do not copy an extra-byte in copy_to_user | From | Jiri Slaby <> |
| |
On 06. 11. 21, 21:48, Pavel Skripkin wrote: > On 11/6/21 23:44, Ajay Garg wrote: >>> > >>> > That's the whole point of the discussion :) >>> > >>> > The method "vt_do_kdgkb_ioctl" does not manage "func_table[kb_func]". >>> > Thus, the method does not know whether or not >>> > strlen(func_table[kb_func]) < sizeof(user_kdgkb->kb_string). >>> > >>> >>> It manages. The code under `case KDSKBSENT:` sets func_table[] entries >>> via vt_kdskbsent(). >>> >>> kbs = strndup_user(..., sizeof(user_kdgkb->kb_string)); >>> >>> is used to allocate buffer for the func_table[] entry. That's my main >>> point :) >> >> func_table is set in vt_kdskbent, which itself is external. >> >> More importantly, vt_kdskbent is handled in case KDSKBSENT:, while the >> strlcpy issue we are dealing with is in case KDGKBSENT: >> In case KDGKBSENT, following are managed : >> >> ssize_t len = sizeof(user_kdgkb->kb_string); >> kbs = kmalloc(len, GFP_KERNEL); >> >> while func_table[kb_func] is external entity here, so no assumption >> ought to be made for it, just my 2 cents though :) >> >> Anyhow, really, it is the maintainers' choice now :), since there >> isn't a burning (compilation/runtime) issue. >> > > I fully agree here, it's maintainer's choice. Let's sit down and wait > what experienced people thing about this :)
I don't quite understand what the problem is. Provided I wrote the code, is there something wrong with this commit (and its explanation), in particular?
commit 6ca03f90527e499dd5e32d6522909e2ad390896b Author: Jiri Slaby <jirislaby@kernel.org> Date: Mon Oct 19 10:55:16 2020 +0200
vt: keyboard, simplify vt_kdgkbsent
Use 'strlen' of the string, add one for NUL terminator and simply do 'copy_to_user' instead of the explicit 'for' loop. This makes the KDGKBSENT case more compact.
The only thing we need to take care about is NULL 'func_table[i]'. Use an empty string in that case.
The original check for overflow could never trigger as the func_buf strings are always shorter or equal to 'struct kbsentry's.
thanks, -- js suse labs
| |