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authorEric W. Biederman <ebiederm@xmission.com>2022-04-11 11:40:14 -0500
committerEric W. Biederman <ebiederm@xmission.com>2022-05-06 14:49:44 -0500
commit343f4c49f2438d8920f1f76fa823ee59b91f02e4 (patch)
treedc166615f16abdd7242245bfe3cc8fd69076a8d1 /fs/exec.c
parent3123109284176b1532874591f7c81f3837bbdc17 (diff)
kthread: Don't allocate kthread_struct for init and umh
If kthread_is_per_cpu runs concurrently with free_kthread_struct the kthread_struct that was just freed may be read from. This bug was introduced by commit 40966e316f86 ("kthread: Ensure struct kthread is present for all kthreads"). When kthread_struct started to be allocated for all tasks that have PF_KTHREAD set. This in turn required the kthread_struct to be freed in kernel_execve and violated the assumption that kthread_struct will have the same lifetime as the task. Looking a bit deeper this only applies to callers of kernel_execve which is just the init process and the user mode helper processes. These processes really don't want to be kernel threads but are for historical reasons. Mostly that copy_thread does not know how to take a kernel mode function to the process with for processes without PF_KTHREAD or PF_IO_WORKER set. Solve this by not allocating kthread_struct for the init process and the user mode helper processes. This is done by adding a kthread member to struct kernel_clone_args. Setting kthread in fork_idle and kernel_thread. Adding user_mode_thread that works like kernel_thread except it does not set kthread. In fork only allocating the kthread_struct if .kthread is set. I have looked at kernel/kthread.c and since commit 40966e316f86 ("kthread: Ensure struct kthread is present for all kthreads") there have been no assumptions added that to_kthread or __to_kthread will not return NULL. There are a few callers of to_kthread or __to_kthread that assume a non-NULL struct kthread pointer will be returned. These functions are kthread_data(), kthread_parmme(), kthread_exit(), kthread(), kthread_park(), kthread_unpark(), kthread_stop(). All of those functions can reasonably expected to be called when it is know that a task is a kthread so that assumption seems reasonable. Cc: stable@vger.kernel.org Fixes: 40966e316f86 ("kthread: Ensure struct kthread is present for all kthreads") Reported-by: Максим Кутявин <maximkabox13@gmail.com> Link: https://lkml.kernel.org/r/20220506141512.516114-1-ebiederm@xmission.com Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Diffstat (limited to 'fs/exec.c')
-rw-r--r--fs/exec.c6
1 files changed, 4 insertions, 2 deletions
diff --git a/fs/exec.c b/fs/exec.c
index e3e55d5e0be1..75eb6e0ee7b2 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1308,8 +1308,6 @@ int begin_new_exec(struct linux_binprm * bprm)
if (retval)
goto out_unlock;
- if (me->flags & PF_KTHREAD)
- free_kthread_struct(me);
me->flags &= ~(PF_RANDOMIZE | PF_FORKNOEXEC | PF_KTHREAD |
PF_NOFREEZE | PF_NO_SETAFFINITY);
flush_thread();
@@ -1955,6 +1953,10 @@ int kernel_execve(const char *kernel_filename,
int fd = AT_FDCWD;
int retval;
+ if (WARN_ON_ONCE((current->flags & PF_KTHREAD) &&
+ (current->worker_private)))
+ return -EINVAL;
+
filename = getname_kernel(kernel_filename);
if (IS_ERR(filename))
return PTR_ERR(filename);