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authorMartin Schwidefsky <schwidefsky@de.ibm.com>2007-10-01 01:20:13 -0700
committerLinus Torvalds <torvalds@woody.linux-foundation.org>2007-10-01 07:52:23 -0700
commit9f96cb1e8bca179a92afa40dfc3c49990f1cfc71 (patch)
tree7d1f921f488aa570083420dc3846856b17a7b2b6 /kernel/futex.c
parent8792f961ba8057d9f27987def3600253a3ba060f (diff)
downloadlinux-9f96cb1e8bca179a92afa40dfc3c49990f1cfc71.tar.bz2
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>
Diffstat (limited to 'kernel/futex.c')
-rw-r--r--kernel/futex.c26
1 files changed, 16 insertions, 10 deletions
diff --git a/kernel/futex.c b/kernel/futex.c
index e8935b195e88..fcc94e7b4086 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -1943,9 +1943,10 @@ static inline int fetch_robust_entry(struct robust_list __user **entry,
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 *curr)
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 *curr)
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 *curr)
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,