Commit-ID: 405c0759712f57b680f66aee9c55cd06ad1cbdef
Gitweb: http://git.kernel.org/tip/405c0759712f57b680f66aee9c55cd06ad1cbdef
Author: Andy Lutomirski <luto@xxxxxxxxxx>
AuthorDate: Mon, 31 Oct 2016 08:11:43 -0700
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Tue, 1 Nov 2016 07:39:17 +0100
fork: Add task stack refcounting sanity check and prevent premature task stack freeing
If something goes wrong with task stack refcounting and a stack
refcount hits zero too early, warn and leak it rather than
potentially freeing it early (and silently).
Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Brian Gerst <brgerst@xxxxxxxxx>
Cc: Denys Vlasenko <dvlasenk@xxxxxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxx>
Cc: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/f29119c783a9680a4b4656e751b6123917ace94b.1477926663.git.luto@xxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
kernel/fork.c | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/kernel/fork.c b/kernel/fork.c
index 623259f..997ac1d 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -315,6 +315,9 @@ static void account_kernel_stack(struct task_struct *tsk, int account)
static void release_task_stack(struct task_struct *tsk)
{
+ if (WARN_ON(tsk->state != TASK_DEAD))
+ return; /* Better to leak the stack than to free prematurely */
+
account_kernel_stack(tsk, -1);
arch_release_thread_stack(tsk->stack);
free_thread_stack(tsk);
@@ -1862,6 +1865,7 @@ bad_fork_cleanup_count:
atomic_dec(&p->cred->user->processes);
exit_creds(p);
bad_fork_free:
+ p->state = TASK_DEAD;
put_task_stack(p);
free_task(p);
fork_out:
--
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