fix set hostname

Previously, when we set hostname:

$ strace hostname abc
...
sethostname("abc", 3) = -1 ENAMETOOLONG (File name too long)
...

According to man 2 sethostname:

"The len argument specifies the number of bytes in name. (Thus, name
does not require a terminating null byte.)"

We wrongly use the CopyStringIn() to check terminating zero byte in
the implementation of sethostname syscall.

To fix this, we use CopyInBytes() instead.

Fixes: #861

Reported-by: chenglang.hy <chenglang.hy@antfin.com>
Signed-off-by: Jianfeng Tan <henry.tjf@antfin.com>

2 files changed, 16 insertions, 4 deletions

diff --git a/pkg/sentry/syscalls/linux/sys_utsname.go b/pkg/sentry/syscalls/linux/sys_utsname.go
index 271ace08e..748e8dd8d 100644
--- a/pkg/sentry/syscalls/linux/sys_utsname.go
+++ b/pkg/sentry/syscalls/linux/sys_utsname.go
@@ -79,11 +79,11 @@ func Sethostname(t *kernel.Task, args arch.SyscallArguments) (uintptr, *kernel.S
 		return 0, nil, syserror.EINVAL
 	}
 
-	name, err := t.CopyInString(nameAddr, int(size))
-	if err != nil {
+	name := make([]byte, size)
+	if _, err := t.CopyInBytes(nameAddr, name); err != nil {
 		return 0, nil, err
 	}
 
-	utsns.SetHostName(name)
+	utsns.SetHostName(string(name))
 	return 0, nil, nil
 }
diff --git a/test/syscalls/linux/uname.cc b/test/syscalls/linux/uname.cc
index 0a5d91017..d8824b171 100644
--- a/test/syscalls/linux/uname.cc
+++ b/test/syscalls/linux/uname.cc
@@ -41,6 +41,19 @@ TEST(UnameTest, Sanity) {
 TEST(UnameTest, SetNames) {
   SKIP_IF(!ASSERT_NO_ERRNO_AND_VALUE(HaveCapability(CAP_SYS_ADMIN)));
 
+  char hostname[65];
+  ASSERT_THAT(sethostname("0123456789", 3), SyscallSucceeds());
+  EXPECT_THAT(gethostname(hostname, sizeof(hostname)), SyscallSucceeds());
+  EXPECT_EQ(absl::string_view(hostname), "012");
+
+  ASSERT_THAT(sethostname("0123456789\0xxx", 11), SyscallSucceeds());
+  EXPECT_THAT(gethostname(hostname, sizeof(hostname)), SyscallSucceeds());
+  EXPECT_EQ(absl::string_view(hostname), "0123456789");
+
+  ASSERT_THAT(sethostname("0123456789\0xxx", 12), SyscallSucceeds());
+  EXPECT_THAT(gethostname(hostname, sizeof(hostname)), SyscallSucceeds());
+  EXPECT_EQ(absl::string_view(hostname), "0123456789");
+
   constexpr char kHostname[] = "wubbalubba";
   ASSERT_THAT(sethostname(kHostname, sizeof(kHostname)), SyscallSucceeds());
 
@@ -54,7 +67,6 @@ TEST(UnameTest, SetNames) {
   EXPECT_EQ(absl::string_view(buf.domainname), kDomainname);
 
   // These should just be glibc wrappers that also call uname(2).
-  char hostname[65];
   EXPECT_THAT(gethostname(hostname, sizeof(hostname)), SyscallSucceeds());
   EXPECT_EQ(absl::string_view(hostname), kHostname);