bpf: mark a NULL kfunc argument precisegrafted

check_kfunc_arg() allows bpf_register_is_null() for nullable arguments
w/o marking the underlying scalar register precise. Hence a checkpoint
created on such a path would prune against arbitrary scalar value.

Fixes: 3bda08b63670 ("bpf: Allow NULL buffers in bpf_dynptr_slice(_rw)")
Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20260904-register-is-null-precise-fixes-v1-5-0f5a360ff15d@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

3 files changed, 45 insertions, 0 deletions

diff --git a/tools/pcmcia/.gitignore b/tools/pcmcia/.gitignore
new file mode 100644
index 000000000..94cb97b77
--- /dev/null
+++ b/tools/pcmcia/.gitignore
@@ -0,0 +1,2 @@
+# SPDX-License-Identifier: GPL-2.0-only
+crc32hash
diff --git a/tools/pcmcia/Makefile b/tools/pcmcia/Makefile
new file mode 100644
index 000000000..eae24df1d
--- /dev/null
+++ b/tools/pcmcia/Makefile
@@ -0,0 +1,10 @@
+# SPDX-License-Identifier: GPL-2.0
+CC := $(CROSS_COMPILE)gcc
+CFLAGS := -I../../usr/include
+
+PROGS := crc32hash
+
+all: $(PROGS)
+
+clean:
+	rm -fr $(PROGS)
diff --git a/tools/pcmcia/crc32hash.c b/tools/pcmcia/crc32hash.c
new file mode 100644
index 000000000..1a18da9cb
--- /dev/null
+++ b/tools/pcmcia/crc32hash.c
@@ -0,0 +1,33 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/* crc32hash.c - derived from linux/lib/crc32.c, GNU GPL v2 */
+/* Usage example:
+$ ./crc32hash "Dual Speed"
+*/
+
+#include <string.h>
+#include <stdio.h>
+#include <ctype.h>
+#include <stdlib.h>
+
+static unsigned int crc32(unsigned char const *p, unsigned int len)
+{
+	int i;
+	unsigned int crc = 0;
+	while (len--) {
+		crc ^= *p++;
+		for (i = 0; i < 8; i++)
+			crc = (crc >> 1) ^ ((crc & 1) ? 0xedb88320 : 0);
+	}
+	return crc;
+}
+
+int main(int argc, char **argv) {
+	unsigned int result;
+	if (argc != 2) {
+		printf("no string passed as argument\n");
+		return -1;
+	}
+	result = crc32((unsigned char const *)argv[1], strlen(argv[1]));
+	printf("0x%x\n", result);
+	return 0;
+}