lib: Reduce user_access_begin() boundaries in strncpy_from_user() and strnlen_user()
The range passed to user_access_begin() by strncpy_from_user() and
strnlen_user() starts at 'src' and goes up to the limit of userspace
although reads will be limited by the 'count' param.
On 32 bits powerpc (book3s/32) access has to be granted for each
256Mbytes segment and the cost increases with the number of segments to
unlock.
Limit the range with 'count' param.
Fixes: 594cc251fdd0 ("make 'user_access_begin()' do 'access_ok()'")
Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/lib/strncpy_from_user.c b/lib/strncpy_from_user.c
index dccb95a..706020b 100644
--- a/lib/strncpy_from_user.c
+++ b/lib/strncpy_from_user.c
@@ -30,13 +30,6 @@
const struct word_at_a_time constants = WORD_AT_A_TIME_CONSTANTS;
unsigned long res = 0;
- /*
- * Truncate 'max' to the user-specified limit, so that
- * we only have one limit we need to check in the loop
- */
- if (max > count)
- max = count;
-
if (IS_UNALIGNED(src, dst))
goto byte_at_a_time;
@@ -114,6 +107,13 @@
unsigned long max = max_addr - src_addr;
long retval;
+ /*
+ * Truncate 'max' to the user-specified limit, so that
+ * we only have one limit we need to check in the loop
+ */
+ if (max > count)
+ max = count;
+
kasan_check_write(dst, count);
check_object_size(dst, count, false);
if (user_access_begin(src, max)) {