Re: [PATCH] robust futex thread exit race
From: Martin Schwidefsky
Date: Sun Sep 30 2007 - 13:32:34 EST
On Sun, 2007-09-30 at 19:11 +0200, Ingo Molnar wrote:
> > > > good catch! A quick preliminary review of your patch indicates it's
> > > > fine - and it might be v2.6.23 material.
> > >
> > > there's a symmetric bug in kernel/compat_futex.c too.
> >
> > True. I'll update the patch and send it again with the Acked-bys.
>
> thanks! Logistics-wise: given that v2.6.22 has this same bug too, it's
> not a .23 regression per se and could in theory be merged after the
> 2.6.23 release too, into 2.6.23.1.
Here we go. Tested with current git and latest glibc tst-robust8 on
s390-64, native and compat.
--
blue skies,
Martin.
"Reality continues to ruin my life." - Calvin.
--
Subject: [PATCH] robust futex thread exit race
From: Martin Schwidefsky <schwidefsky@xxxxxxxxxx>
Calling handle_futex_death in exit_robust_list for the different
robust mutexes of a thread basically frees the mutex. Another
thread might grab the lock immediately which updates the next
pointer of the mutex. fetch_robust_entry over the next pointer
might therefore branch into the robust mutex list of a different
thread. This can cause two problems: 1) some mutexes held by
the dead thread are not getting freed and 2) some mutexs held by
a different thread are freed.
The next pointer need to be read before calling fetch_robust_entry.
Signed-off-by: Martin Schwidefsky <schwidefsky@xxxxxxxxxx>
Acked-by: Ingo Molnar <mingo@xxxxxxx>
Acked-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
---
kernel/futex.c | 26 ++++++++++++++++----------
kernel/futex_compat.c | 28 ++++++++++++++++++----------
2 files changed, 34 insertions(+), 20 deletions(-)
diff -urpN linux-2.6/kernel/futex.c linux-2.6-patched/kernel/futex.c
--- linux-2.6/kernel/futex.c 2007-08-23 11:14:33.000000000 +0200
+++ linux-2.6-patched/kernel/futex.c 2007-09-30 19:23:12.000000000 +0200
@@ -1943,9 +1943,10 @@ static inline int fetch_robust_entry(str
void exit_robust_list(struct task_struct *curr)
{
struct robust_list_head __user *head = curr->robust_list;
- struct robust_list __user *entry, *pending;
- unsigned int limit = ROBUST_LIST_LIMIT, pi, pip;
+ struct robust_list __user *entry, *next_entry, *pending;
+ unsigned int limit = ROBUST_LIST_LIMIT, pi, next_pi, pip;
unsigned long futex_offset;
+ int rc;
/*
* Fetch the list head (which was registered earlier, via
@@ -1965,12 +1966,14 @@ void exit_robust_list(struct task_struct
if (fetch_robust_entry(&pending, &head->list_op_pending, &pip))
return;
- if (pending)
- handle_futex_death((void __user *)pending + futex_offset,
- curr, pip);
-
+ next_entry = NULL; /* avoid warning with gcc */
while (entry != &head->list) {
/*
+ * Fetch the next entry in the list before calling
+ * handle_futex_death:
+ */
+ rc = fetch_robust_entry(&next_entry, &entry->next, &next_pi);
+ /*
* A pending lock might already be on the list, so
* don't process it twice:
*/
@@ -1978,11 +1981,10 @@ void exit_robust_list(struct task_struct
if (handle_futex_death((void __user *)entry + futex_offset,
curr, pi))
return;
- /*
- * Fetch the next entry in the list:
- */
- if (fetch_robust_entry(&entry, &entry->next, &pi))
+ if (rc)
return;
+ entry = next_entry;
+ pi = next_pi;
/*
* Avoid excessively long or circular lists:
*/
@@ -1991,6 +1993,10 @@ void exit_robust_list(struct task_struct
cond_resched();
}
+
+ if (pending)
+ handle_futex_death((void __user *)pending + futex_offset,
+ curr, pip);
}
long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout,
diff -urpN linux-2.6/kernel/futex_compat.c linux-2.6-patched/kernel/futex_compat.c
--- linux-2.6/kernel/futex_compat.c 2007-09-12 10:29:09.000000000 +0200
+++ linux-2.6-patched/kernel/futex_compat.c 2007-09-30 18:29:16.000000000 +0200
@@ -38,10 +38,11 @@ fetch_robust_entry(compat_uptr_t *uentry
void compat_exit_robust_list(struct task_struct *curr)
{
struct compat_robust_list_head __user *head = curr->compat_robust_list;
- struct robust_list __user *entry, *pending;
- unsigned int limit = ROBUST_LIST_LIMIT, pi, pip;
- compat_uptr_t uentry, upending;
+ struct robust_list __user *entry, *next_entry, *pending;
+ unsigned int limit = ROBUST_LIST_LIMIT, pi, next_pi, pip;
+ compat_uptr_t uentry, next_uentry, upending;
compat_long_t futex_offset;
+ int rc;
/*
* Fetch the list head (which was registered earlier, via
@@ -61,11 +62,16 @@ void compat_exit_robust_list(struct task
if (fetch_robust_entry(&upending, &pending,
&head->list_op_pending, &pip))
return;
- if (pending)
- handle_futex_death((void __user *)pending + futex_offset, curr, pip);
+ next_entry = NULL; /* avoid warning with gcc */
while (entry != (struct robust_list __user *) &head->list) {
/*
+ * Fetch the next entry in the list before calling
+ * handle_futex_death:
+ */
+ rc = fetch_robust_entry(&next_uentry, &next_entry,
+ (compat_uptr_t __user *)&entry->next, &next_pi);
+ /*
* A pending lock might already be on the list, so
* dont process it twice:
*/
@@ -74,12 +80,11 @@ void compat_exit_robust_list(struct task
curr, pi))
return;
- /*
- * Fetch the next entry in the list:
- */
- if (fetch_robust_entry(&uentry, &entry,
- (compat_uptr_t __user *)&entry->next, &pi))
+ if (rc)
return;
+ uentry = next_uentry;
+ entry = next_entry;
+ pi = next_pi;
/*
* Avoid excessively long or circular lists:
*/
@@ -88,6 +93,9 @@ void compat_exit_robust_list(struct task
cond_resched();
}
+ if (pending)
+ handle_futex_death((void __user *)pending + futex_offset,
+ curr, pip);
}
asmlinkage long
-
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