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| author | Martin Schwidefsky <schwidefsky@de.ibm.com> | 2007-10-01 10:20:13 +0200 |
|---|---|---|
| committer | Linus Torvalds <torvalds@woody.linux-foundation.org> | 2007-10-01 16:52:23 +0200 |
| commit | 9f96cb1e8bca179a92afa40dfc3c49990f1cfc71 (patch) | |
| tree | 7d1f921f488aa570083420dc3846856b17a7b2b6 /kernel/futex.c | |
| parent | VT ioctl race fix (diff) | |
| download | linux-9f96cb1e8bca179a92afa40dfc3c49990f1cfc71.tar.xz linux-9f96cb1e8bca179a92afa40dfc3c49990f1cfc71.zip | |
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.c | 26 |
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, |