On Tue, 24 Feb 2026 at 23:41, Kees Cook <[email protected]> wrote: > > On Tue, Feb 24, 2026 at 01:48:51PM -0800, Kees Cook wrote: > > On Tue, Feb 24, 2026 at 11:09:44AM +0100, Marco Elver wrote: > > > On Mon, 23 Feb 2026 at 23:22, Kees Cook <[email protected]> wrote: > > > > > > > > Instead of depending on the implicit case between a pointer to pointers > > > > and pointer to arrays, use the assigned variable type for the allocation > > > > type so they correctly match. Solves the following build error: > > > > > > > > ../kernel/kcsan/kcsan_test.c: In function '__report_matches': > > > > ../kernel/kcsan/kcsan_test.c:171:16: error: assignment to 'char > > > > (*)[512]' from incompatible pointer type 'char (*)[3][512]' > > > > [-Wincompatible-pointer-types] > > > > 171 | expect = kmalloc_obj(observed.lines); > > > > | ^ > > > > > > > > Tested with: > > > > > > > > $ ./tools/testing/kunit/kunit.py run \ > > > > --kconfig_add CONFIG_DEBUG_KERNEL=y \ > > > > --kconfig_add CONFIG_KCSAN=y \ > > > > --kconfig_add CONFIG_KCSAN_KUNIT_TEST=y \ > > > > --arch=x86_64 --qemu_args '-smp 2' kcsan > > > > > > > > Reported-by: Nathan Chancellor <[email protected]> > > > > Fixes: 69050f8d6d07 ("treewide: Replace kmalloc with kmalloc_obj for > > > > non-scalar types") > > > > Signed-off-by: Kees Cook <[email protected]> > > > > --- > > > > Cc: Marco Elver <[email protected]> > > > > Cc: Dmitry Vyukov <[email protected]> > > > > Cc: <[email protected]> > > > > --- > > > > kernel/kcsan/kcsan_test.c | 2 +- > > > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > > > > > diff --git a/kernel/kcsan/kcsan_test.c b/kernel/kcsan/kcsan_test.c > > > > index 79e655ea4ca1..056fa859ad9a 100644 > > > > --- a/kernel/kcsan/kcsan_test.c > > > > +++ b/kernel/kcsan/kcsan_test.c > > > > @@ -168,7 +168,7 @@ static bool __report_matches(const struct > > > > expect_report *r) > > > > if (!report_available()) > > > > return false; > > > > > > > > - expect = kmalloc_obj(observed.lines); > > > > + expect = kmalloc_obj(*expect); > > > > > > This is wrong. Instead of allocating 3x512 bytes it's now only > > > allocating 512 bytes, so we get OOB below with this change. 'expect' > > > is a pointer to a 3-dimensional array of 512-char arrays (matching > > > observed.lines). > > > > Why did running the kunit test not trip over this? :( > > > > Hmpf, getting arrays allocated without an explicit cast seems to be > > impossible. How about this: > > > > > > diff --git a/kernel/kcsan/kcsan_test.c b/kernel/kcsan/kcsan_test.c > > index 056fa859ad9a..ae758150ccb9 100644 > > --- a/kernel/kcsan/kcsan_test.c > > +++ b/kernel/kcsan/kcsan_test.c > > @@ -168,7 +168,7 @@ static bool __report_matches(const struct expect_report > > *r) > > if (!report_available()) > > return false; > > > > - expect = kmalloc_obj(*expect); > > + expect = (typeof(expect))kmalloc_obj(observed.lines); > > if (WARN_ON(!expect)) > > return false; > > Or: > > expect = kmalloc_objs(*observed.lines, ARRAY_SIZE(observed.lines)); > > I think the quoted cast is probably better...
The cast is easier to read (no indirection needed to understand it's just allocating same size as observed.lines).
