[PATCH] selftests/mm: handle fork() failure in migration tests

[Hu Song]

From: Song Hu <husong@xxxxxxxxxx>

When fork() fails and returns -1, the code falls into the else branch
and stores -1 into self->pids[i]. Later, kill(-1, SIGTERM) is called
which sends SIGTERM to every process the user has permission to signal,
potentially killing the entire user session.

Add an explicit check for fork() returning -1 (pid < 0). On failure,
clean up any already-forked children before failing the test via
ASSERT_GE(pid, 0). This fix is applied to all three fork() call sites
in shared_anon, shared_anon_thp, and shared_anon_htlb tests.

Signed-off-by: Hu Song <husong@xxxxxxxxxx>
---
 tools/testing/selftests/mm/migration.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/tools/testing/selftests/mm/migration.c b/tools/testing/selftests/mm/migration.c
index 60e78bbfc0e3..f433e4f195ad 100644
--- a/tools/testing/selftests/mm/migration.c
+++ b/tools/testing/selftests/mm/migration.c
@@ -163,6 +163,11 @@ TEST_F_TIMEOUT(migration, shared_anon, 2*RUNTIME)
 	memset(ptr, 0xde, TWOMEG);
 	for (i = 0; i < self->nthreads - 1; i++) {
 		pid = fork();
+		if (pid < 0) {
+			while (--i >= 0)
+				kill(self->pids[i], SIGTERM);
+			ASSERT_GE(pid, 0);
+		}
 		if (!pid) {
 			prctl(PR_SET_PDEATHSIG, SIGHUP);
 			/* Parent may have died before prctl so check now. */
@@ -235,6 +240,11 @@ TEST_F_TIMEOUT(migration, shared_anon_thp, 2*RUNTIME)
 	memset(ptr, 0xde, TWOMEG);
 	for (i = 0; i < self->nthreads - 1; i++) {
 		pid = fork();
+		if (pid < 0) {
+			while (--i >= 0)
+				kill(self->pids[i], SIGTERM);
+			ASSERT_GE(pid, 0);
+		}
 		if (!pid) {
 			prctl(PR_SET_PDEATHSIG, SIGHUP);
 			/* Parent may have died before prctl so check now. */
@@ -295,6 +305,11 @@ TEST_F_TIMEOUT(migration, shared_anon_htlb, 2*RUNTIME)
 	memset(ptr, 0xde, TWOMEG);
 	for (i = 0; i < self->nthreads - 1; i++) {
 		pid = fork();
+		if (pid < 0) {
+			while (--i >= 0)
+				kill(self->pids[i], SIGTERM);
+			ASSERT_GE(pid, 0);
+		}
 		if (!pid) {
 			prctl(PR_SET_PDEATHSIG, SIGHUP);
 			/* Parent may have died before prctl so check now. */
-- 
2.25.1