netdev - [PATCH bpf-next] bpf: fix segmentation fault of test

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Date:   Sat,  8 Aug 2020 01:20:16 +0800
From:   Jianlin Lv <Jianlin.Lv@....com>
To:     bpf@...r.kernel.org
Cc:     davem@...emloft.net, kuba@...nel.org, ast@...nel.org,
        daniel@...earbox.net, yhs@...com, Jianlin.Lv@....com,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: [PATCH bpf-next] bpf: fix segmentation fault of test_progs

test_progs reports the segmentation fault as below

$ sudo ./test_progs -t mmap --verbose
test_mmap:PASS:skel_open_and_load 0 nsec
......
test_mmap:PASS:adv_mmap1 0 nsec
test_mmap:PASS:adv_mmap2 0 nsec
test_mmap:PASS:adv_mmap3 0 nsec
test_mmap:PASS:adv_mmap4 0 nsec
Segmentation fault

This issue was triggered because mmap() and munmap() used inconsistent
length parameters; mmap() creates a new mapping of 3*page_size, but the
length parameter set in the subsequent re-map and munmap() functions is
4*page_size; this leads to the destruction of the process space.

Another issue is that when unmap the second page fails, the length
parameter to delete tmp1 mappings should be 3*page_size.

Signed-off-by: Jianlin Lv <Jianlin.Lv@....com>
---
 tools/testing/selftests/bpf/prog_tests/mmap.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/tools/testing/selftests/bpf/prog_tests/mmap.c b/tools/testing/selftests/bpf/prog_tests/mmap.c
index 43d0b5578f46..2070cfe19cac 100644
--- a/tools/testing/selftests/bpf/prog_tests/mmap.c
+++ b/tools/testing/selftests/bpf/prog_tests/mmap.c
@@ -192,7 +192,7 @@ void test_mmap(void)
 	/* unmap second page: pages 1, 3 mapped */
 	err = munmap(tmp1 + page_size, page_size);
 	if (CHECK(err, "adv_mmap2", "errno %d\n", errno)) {
-		munmap(tmp1, map_sz);
+		munmap(tmp1, 3 * page_size);
 		goto cleanup;
 	}
 
@@ -207,8 +207,8 @@ void test_mmap(void)
 	CHECK(tmp1 + page_size != tmp2, "adv_mmap4",
 	      "tmp1: %p, tmp2: %p\n", tmp1, tmp2);
 
-	/* re-map all 4 pages */
-	tmp2 = mmap(tmp1, 4 * page_size, PROT_READ, MAP_SHARED | MAP_FIXED,
+	/* re-map all 3 pages */
+	tmp2 = mmap(tmp1, 3 * page_size, PROT_READ, MAP_SHARED | MAP_FIXED,
 		    data_map_fd, 0);
 	if (CHECK(tmp2 == MAP_FAILED, "adv_mmap5", "errno %d\n", errno)) {
 		munmap(tmp1, 3 * page_size); /* unmap page 1 */
@@ -226,7 +226,7 @@ void test_mmap(void)
 	CHECK_FAIL(map_data->val[2] != 321);
 	CHECK_FAIL(map_data->val[far] != 3 * 321);
 
-	munmap(tmp2, 4 * page_size);
+	munmap(tmp2, 3 * page_size);
 
 	/* map all 4 pages, but with pg_off=1 page, should fail */
 	tmp1 = mmap(NULL, 4 * page_size, PROT_READ, MAP_SHARED | MAP_FIXED,
-- 
2.17.1