[tip:core/urgent] fork: Add task stack refcounting sanity check and prevent premature task stack freeing

[tip-bot for Andy Lutomirski]

Commit-ID:  405c0759712f57b680f66aee9c55cd06ad1cbdef
Gitweb: http://git.kernel.org/tip/405c0759712f57b680f66aee9c55cd06ad1cbdef
Author: Andy Lutomirski 
AuthorDate: Mon, 31 Oct 2016 08:11:43 -0700
Committer:  Ingo Molnar 
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 
Cc: Borislav Petkov 
Cc: Brian Gerst 
Cc: Denys Vlasenko 
Cc: H. Peter Anvin 
Cc: Josh Poimboeuf 
Cc: Linus Torvalds 
Cc: Oleg Nesterov 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Link: 
http://lkml.kernel.org/r/f29119c783a9680a4b4656e751b6123917ace94b.1477926663.git.l...@kernel.org
Signed-off-by: Ingo Molnar 
---
 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(>cred->user->processes);
exit_creds(p);
 bad_fork_free:
+   p->state = TASK_DEAD;
put_task_stack(p);
free_task(p);
 fork_out:

[tip:core/urgent] fork: Add task stack refcounting sanity check and prevent premature task stack freeing

[tip-bot for Andy Lutomirski]

Commit-ID:  405c0759712f57b680f66aee9c55cd06ad1cbdef
Gitweb: http://git.kernel.org/tip/405c0759712f57b680f66aee9c55cd06ad1cbdef
Author: Andy Lutomirski 
AuthorDate: Mon, 31 Oct 2016 08:11:43 -0700
Committer:  Ingo Molnar 
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 
Cc: Borislav Petkov 
Cc: Brian Gerst 
Cc: Denys Vlasenko 
Cc: H. Peter Anvin 
Cc: Josh Poimboeuf 
Cc: Linus Torvalds 
Cc: Oleg Nesterov 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Link: 
http://lkml.kernel.org/r/f29119c783a9680a4b4656e751b6123917ace94b.1477926663.git.l...@kernel.org
Signed-off-by: Ingo Molnar 
---
 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(>cred->user->processes);
exit_creds(p);
 bad_fork_free:
+   p->state = TASK_DEAD;
put_task_stack(p);
free_task(p);
 fork_out: