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-rw-r--r--include/linux/fortify-string.h10
-rw-r--r--lib/strscpy_kunit.c13
2 files changed, 23 insertions, 0 deletions
diff --git a/include/linux/fortify-string.h b/include/linux/fortify-string.h
index 49782f63f015..32a66d4b30ca 100644
--- a/include/linux/fortify-string.h
+++ b/include/linux/fortify-string.h
@@ -314,6 +314,16 @@ __FORTIFY_INLINE ssize_t strscpy(char * const POS p, const char * const POS q, s
if (__compiletime_lessthan(p_size, size))
__write_overflow();
+ /* Short-circuit for compile-time known-safe lengths. */
+ if (__compiletime_lessthan(p_size, SIZE_MAX)) {
+ len = __compiletime_strlen(q);
+
+ if (len < SIZE_MAX && __compiletime_lessthan(len, size)) {
+ __underlying_memcpy(p, q, len + 1);
+ return len;
+ }
+ }
+
/*
* This call protects from read overflow, because len will default to q
* length if it smaller than size.
diff --git a/lib/strscpy_kunit.c b/lib/strscpy_kunit.c
index 98523f828d3a..a6b6344354ed 100644
--- a/lib/strscpy_kunit.c
+++ b/lib/strscpy_kunit.c
@@ -81,6 +81,8 @@ static void tc(struct kunit *test, char *src, int count, int expected,
static void strscpy_test(struct kunit *test)
{
+ char dest[8];
+
/*
* tc() uses a destination buffer of size 6 and needs at
* least 2 characters spare (one for null and one to check for
@@ -111,6 +113,17 @@ static void strscpy_test(struct kunit *test)
tc(test, "ab", 4, 2, 2, 1, 1);
tc(test, "a", 4, 1, 1, 1, 2);
tc(test, "", 4, 0, 0, 1, 3);
+
+ /* Compile-time-known source strings. */
+ KUNIT_EXPECT_EQ(test, strscpy(dest, "", ARRAY_SIZE(dest)), 0);
+ KUNIT_EXPECT_EQ(test, strscpy(dest, "", 3), 0);
+ KUNIT_EXPECT_EQ(test, strscpy(dest, "", 1), 0);
+ KUNIT_EXPECT_EQ(test, strscpy(dest, "", 0), -E2BIG);
+ KUNIT_EXPECT_EQ(test, strscpy(dest, "Fixed", ARRAY_SIZE(dest)), 5);
+ KUNIT_EXPECT_EQ(test, strscpy(dest, "Fixed", 3), -E2BIG);
+ KUNIT_EXPECT_EQ(test, strscpy(dest, "Fixed", 1), -E2BIG);
+ KUNIT_EXPECT_EQ(test, strscpy(dest, "Fixed", 0), -E2BIG);
+ KUNIT_EXPECT_EQ(test, strscpy(dest, "This is too long", ARRAY_SIZE(dest)), -E2BIG);
}
static struct kunit_case strscpy_test_cases[] = {