Don't mask errors in createAt loop.

The error set in the loop in createAt was being masked
by other errors declared with ":=". This allowed an
ErrResolveViaReadlink error to escape, which can cause
a sentry panic.

Added test case which repros without the fix.

PiperOrigin-RevId: 257061767

1 files changed, 15 insertions, 0 deletions

diff --git a/test/syscalls/linux/symlink.cc b/test/syscalls/linux/symlink.cc
index 69650a1d3..b249ff91f 100644
--- a/test/syscalls/linux/symlink.cc
+++ b/test/syscalls/linux/symlink.cc
@@ -325,6 +325,21 @@ TEST_P(ParamSymlinkTest, CreateExistingSelfLink) {
   ASSERT_THAT(unlink(linkpath.c_str()), SyscallSucceeds());
 }
 
+// Test that opening a file that is a symlink to its parent directory fails
+// with ELOOP.
+TEST_P(ParamSymlinkTest, CreateExistingParentLink) {
+  ASSERT_THAT(chdir(GetAbsoluteTestTmpdir().c_str()), SyscallSucceeds());
+
+  const std::string linkpath = GetParam();
+  const std::string target = JoinPath(linkpath, "child");
+  ASSERT_THAT(symlink(target.c_str(), linkpath.c_str()), SyscallSucceeds());
+
+  EXPECT_THAT(open(linkpath.c_str(), O_CREAT, 0666),
+              SyscallFailsWithErrno(ELOOP));
+
+  ASSERT_THAT(unlink(linkpath.c_str()), SyscallSucceeds());
+}
+
 // Test that opening an existing symlink with O_CREAT|O_EXCL will fail with
 // EEXIST.
 TEST_P(ParamSymlinkTest, OpenLinkExclFails) {