[PATCH AUTOSEL 5.8 21/63] selftests/bpf: Fix segmentation fault in test_progs

From: Sasha Levin
Date: Mon Aug 24 2020 - 13:28:01 EST


From: Jianlin Lv <Jianlin.Lv@xxxxxxx>

[ Upstream commit 0390c429dbed4068bd2cd8dded937d9a5ec24cd2 ]

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.

To fix this issue, first create 4 pages of anonymous mapping, then do all
the mmap() with MAP_FIXED.

Another issue is that when unmap the second page fails, the length
parameter to delete tmp1 mappings should be 4 * page_size.

Signed-off-by: Jianlin Lv <Jianlin.Lv@xxxxxxx>
Signed-off-by: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
Acked-by: Andrii Nakryiko <andriin@xxxxxx>
Link: https://lore.kernel.org/bpf/20200810153940.125508-1-Jianlin.Lv@xxxxxxx
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
tools/testing/selftests/bpf/prog_tests/mmap.c | 19 +++++++++++++------
1 file changed, 13 insertions(+), 6 deletions(-)

diff --git a/tools/testing/selftests/bpf/prog_tests/mmap.c b/tools/testing/selftests/bpf/prog_tests/mmap.c
index 43d0b5578f461..9c3c5c0f068fb 100644
--- a/tools/testing/selftests/bpf/prog_tests/mmap.c
+++ b/tools/testing/selftests/bpf/prog_tests/mmap.c
@@ -21,7 +21,7 @@ void test_mmap(void)
const long page_size = sysconf(_SC_PAGE_SIZE);
int err, duration = 0, i, data_map_fd, data_map_id, tmp_fd, rdmap_fd;
struct bpf_map *data_map, *bss_map;
- void *bss_mmaped = NULL, *map_mmaped = NULL, *tmp1, *tmp2;
+ void *bss_mmaped = NULL, *map_mmaped = NULL, *tmp0, *tmp1, *tmp2;
struct test_mmap__bss *bss_data;
struct bpf_map_info map_info;
__u32 map_info_sz = sizeof(map_info);
@@ -183,16 +183,23 @@ void test_mmap(void)

/* check some more advanced mmap() manipulations */

+ tmp0 = mmap(NULL, 4 * page_size, PROT_READ, MAP_SHARED | MAP_ANONYMOUS,
+ -1, 0);
+ if (CHECK(tmp0 == MAP_FAILED, "adv_mmap0", "errno %d\n", errno))
+ goto cleanup;
+
/* map all but last page: pages 1-3 mapped */
- tmp1 = mmap(NULL, 3 * page_size, PROT_READ, MAP_SHARED,
+ tmp1 = mmap(tmp0, 3 * page_size, PROT_READ, MAP_SHARED | MAP_FIXED,
data_map_fd, 0);
- if (CHECK(tmp1 == MAP_FAILED, "adv_mmap1", "errno %d\n", errno))
+ if (CHECK(tmp0 != tmp1, "adv_mmap1", "tmp0: %p, tmp1: %p\n", tmp0, tmp1)) {
+ munmap(tmp0, 4 * page_size);
goto cleanup;
+ }

/* 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, 4 * page_size);
goto cleanup;
}

@@ -201,7 +208,7 @@ void test_mmap(void)
MAP_SHARED | MAP_FIXED, data_map_fd, 0);
if (CHECK(tmp2 == MAP_FAILED, "adv_mmap3", "errno %d\n", errno)) {
munmap(tmp1, page_size);
- munmap(tmp1 + 2*page_size, page_size);
+ munmap(tmp1 + 2*page_size, 2 * page_size);
goto cleanup;
}
CHECK(tmp1 + page_size != tmp2, "adv_mmap4",
@@ -211,7 +218,7 @@ void test_mmap(void)
tmp2 = mmap(tmp1, 4 * 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 */
+ munmap(tmp1, 4 * page_size); /* unmap page 1 */
goto cleanup;
}
CHECK(tmp1 != tmp2, "adv_mmap6", "tmp1: %p, tmp2: %p\n", tmp1, tmp2);
--
2.25.1