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robust futex thread exit race 

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 point need to be read before calling handle_futex_death.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Acked-by: Ingo Molnar <mingo@elte.hu>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Martin Schwidefsky 2007-10-01 01:20:13 -07:00 committed by Linus Torvalds
parent 8792f961ba
commit 9f96cb1e8b
2 changed files with 34 additions and 20 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

26
kernel/futex.c
View File

@ -1943,9 +1943,10 @@ static inline int fetch_robust_entry(struct robust_list __user **entry,
void exit_robust_list(struct task_struct *curr) void exit_robust_list(struct task_struct *curr)
{ {
struct robust_list_head __user *head = curr->robust_list; struct robust_list_head __user *head = curr->robust_list;
struct robust_list __user *entry, *pending; struct robust_list __user *entry, *next_entry, *pending;
unsigned int limit = ROBUST_LIST_LIMIT, pi, pip; unsigned int limit = ROBUST_LIST_LIMIT, pi, next_pi, pip;
unsigned long futex_offset; unsigned long futex_offset;
int rc;
/* /*
* Fetch the list head (which was registered earlier, via * Fetch the list head (which was registered earlier, via
@ -1965,11 +1966,13 @@ void exit_robust_list(struct task_struct *curr)
if (fetch_robust_entry(&pending, &head->list_op_pending, &pip)) if (fetch_robust_entry(&pending, &head->list_op_pending, &pip))
return; return;
if (pending) next_entry = NULL; /* avoid warning with gcc */
handle_futex_death((void __user *)pending + futex_offset,
curr, pip);
while (entry != &head->list) { 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 * A pending lock might already be on the list, so
* don't process it twice: * don't process it twice:
@ -1978,11 +1981,10 @@ void exit_robust_list(struct task_struct *curr)
if (handle_futex_death((void __user *)entry + futex_offset, if (handle_futex_death((void __user *)entry + futex_offset,
curr, pi)) curr, pi))
return; return;
/* if (rc)
* Fetch the next entry in the list:
*/
if (fetch_robust_entry(&entry, &entry->next, &pi))
return; return;
entry = next_entry;
pi = next_pi;
/* /*
* Avoid excessively long or circular lists: * Avoid excessively long or circular lists:
*/ */
@ -1991,6 +1993,10 @@ void exit_robust_list(struct task_struct *curr)
cond_resched(); 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, long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout,

28
kernel/futex_compat.c
View File

@ -38,10 +38,11 @@ fetch_robust_entry(compat_uptr_t *uentry, struct robust_list __user **entry,
void compat_exit_robust_list(struct task_struct *curr) void compat_exit_robust_list(struct task_struct *curr)
{ {
struct compat_robust_list_head __user *head = curr->compat_robust_list; struct compat_robust_list_head __user *head = curr->compat_robust_list;
struct robust_list __user *entry, *pending; struct robust_list __user *entry, *next_entry, *pending;
unsigned int limit = ROBUST_LIST_LIMIT, pi, pip; unsigned int limit = ROBUST_LIST_LIMIT, pi, next_pi, pip;
compat_uptr_t uentry, upending; compat_uptr_t uentry, next_uentry, upending;
compat_long_t futex_offset; compat_long_t futex_offset;
int rc;
/* /*
* Fetch the list head (which was registered earlier, via * Fetch the list head (which was registered earlier, via
@ -61,10 +62,15 @@ void compat_exit_robust_list(struct task_struct *curr)
if (fetch_robust_entry(&upending, &pending, if (fetch_robust_entry(&upending, &pending,
&head->list_op_pending, &pip)) &head->list_op_pending, &pip))
return; 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) { 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 * A pending lock might already be on the list, so
* dont process it twice: * dont process it twice:
@ -74,12 +80,11 @@ void compat_exit_robust_list(struct task_struct *curr)
curr, pi)) curr, pi))
return; return;
/* if (rc)
* Fetch the next entry in the list:
*/
if (fetch_robust_entry(&uentry, &entry,
(compat_uptr_t __user *)&entry->next, &pi))
return; return;
uentry = next_uentry;
entry = next_entry;
pi = next_pi;
/* /*
* Avoid excessively long or circular lists: * Avoid excessively long or circular lists:
*/ */
@ -88,6 +93,9 @@ void compat_exit_robust_list(struct task_struct *curr)
cond_resched(); cond_resched();
} }
if (pending)
handle_futex_death((void __user *)pending + futex_offset,
curr, pip);
} }
asmlinkage long asmlinkage long