From f957fb23cf68e72084c7b50569242a07997f96bc Mon Sep 17 00:00:00 2001 From: "chris.zn" Date: Thu, 20 Jun 2019 15:19:05 +0800 Subject: Return ENOENT when reading /proc/{pid}/task of an exited process There will be a deadloop when we use getdents to read /proc/{pid}/task of an exited process Like this: Process A is running Process B: open /proc/{pid of A}/task Process A exits Process B: getdents /proc/{pid of A}/task Then, process B will fall into deadloop, and return "." and ".." in loops and never ends. This patch returns ENOENT when use getdents to read /proc/{pid}/task if the process is just exited. Signed-off-by: chris.zn --- pkg/sentry/fs/proc/task.go | 7 ++++++- test/syscalls/linux/proc.cc | 19 +++++++++++++++++++ 2 files changed, 25 insertions(+), 1 deletion(-) diff --git a/pkg/sentry/fs/proc/task.go b/pkg/sentry/fs/proc/task.go index b2e36aeee..22554bb88 100644 --- a/pkg/sentry/fs/proc/task.go +++ b/pkg/sentry/fs/proc/task.go @@ -20,6 +20,7 @@ import ( "io" "sort" "strconv" + "syscall" "gvisor.dev/gvisor/pkg/abi/linux" "gvisor.dev/gvisor/pkg/sentry/context" @@ -162,6 +163,11 @@ func (f *subtasksFile) Readdir(ctx context.Context, file *fs.File, ser fs.Dentry // subtask to emit. offset := file.Offset() + tasks := f.t.ThreadGroup().MemberIDs(f.pidns) + if len(tasks) == 0 { + return offset, syscall.ENOENT + } + if offset == 0 { // Serialize "." and "..". root := fs.RootFromContext(ctx) @@ -178,7 +184,6 @@ func (f *subtasksFile) Readdir(ctx context.Context, file *fs.File, ser fs.Dentry } // Serialize tasks. - tasks := f.t.ThreadGroup().MemberIDs(f.pidns) taskInts := make([]int, 0, len(tasks)) for _, tid := range tasks { taskInts = append(taskInts, int(tid)) diff --git a/test/syscalls/linux/proc.cc b/test/syscalls/linux/proc.cc index 924b98e3a..2177665c8 100644 --- a/test/syscalls/linux/proc.cc +++ b/test/syscalls/linux/proc.cc @@ -1908,6 +1908,25 @@ void CheckDuplicatesRecursively(std::string path) { TEST(Proc, NoDuplicates) { CheckDuplicatesRecursively("/proc"); } +TEST(Proc, Getdents) { + int child_pid = fork(); + ASSERT_GE(child_pid, 0); + if (child_pid == 0) { + while(1){ + sleep(100); + } + } + ASSERT_THAT(child_pid, SyscallSucceeds()); + char name[100]; + char buf[1024]; + int fd; + sprintf(name, "/proc/%d/task", child_pid); + fd = open(name, O_RDONLY | O_DIRECTORY); + ASSERT_THAT(kill(child_pid, SIGKILL), SyscallSucceeds()); + ASSERT_THAT(waitpid(child_pid, NULL, 0), SyscallSucceedsWithValue(child_pid)); + ASSERT_THAT(syscall(SYS_getdents, fd, buf, 1024), SyscallFailsWithErrno(ENOENT)); +} + // Most /proc/PID files are owned by the task user with SUID_DUMP_USER. TEST(ProcPid, UserDumpableOwner) { int before; -- cgit v1.2.3