Messages in this thread | | | Date | Sat, 6 Nov 2021 23:18:27 +0300 | Subject | Re: [PATCH] tty: vt: keyboard: do not copy an extra-byte in copy_to_user | From | Pavel Skripkin <> |
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On 11/6/21 22:46, Ajay Garg wrote: > Actually, on further thoughts, even David's solution will require an > extra check, if -E2BIG is returned. > > So, I guess the solution suggested by me looks the best > (https://lore.kernel.org/linux-serial/868025b485b94480ad17d0ec971b3ee9@AcuMS.aculab.com/T/#m1c4aaa4347b02fd4c11ce611ff5029fcb71c37a1) > : > > 1. > == Do not use the return value from strlcpy. == > > len = strlcpy(kbs, func_table[kb_func] ? : "", len); > => > strlcpy(kbs, func_table[kb_func] ? : "", len); > > > 2. > == Calculate the actual length of kbs, add 1, and then copy those many > bytes to user-buffer == > > ret = copy_to_user(user_kdgkb->kb_string, kbs, len + 1) ? > -EFAULT : 0; > => > ret = copy_to_user(user_kdgkb->kb_string, kbs, strlen(kbs) + 1) ? > -EFAULT : 0; >
But isn't strlen(kbs) is guaranteed to be equal to strlcpy() return value in this case? As I said in previous emails, strlen(func_table[kb_func]) < sizeof(user_kdgkb->kb_string) by design of this function.
Do we need extra strlen() call here? Let's see what more experienced people think about it :)
With regards, Pavel Skripkin
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