s390/uaccess: fix strncpy_from_user/strnlen_user zero maxlen case
If the maximum length specified for the to be accessed string for
strncpy_from_user() and strnlen_user() is zero the following incorrect
values would be returned or incorrect memory accesses would happen:
strnlen_user_std() and strnlen_user_pt() incorrectly return "1"
strncpy_from_user_pt() would incorrectly access "dst[maxlen - 1]"
strncpy_from_user_mvcos() would incorrectly return "-EFAULT"
Fix all these oddities by adding early checks.
Reviewed-by: Gerald Schaefer <gerald.schaefer@de.ibm.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
diff --git a/arch/s390/lib/uaccess_std.c b/arch/s390/lib/uaccess_std.c
index 6fbd063..79c6c7d7 100644
--- a/arch/s390/lib/uaccess_std.c
+++ b/arch/s390/lib/uaccess_std.c
@@ -188,6 +188,8 @@
register unsigned long reg0 asm("0") = 0UL;
unsigned long tmp1, tmp2;
+ if (unlikely(!size))
+ return 0;
asm volatile(
" la %2,0(%1)\n"
" la %3,0(%0,%1)\n"