From 9f96cb1e8bca179a92afa40dfc3c49990f1cfc71 Mon Sep 17 00:00:00 2001 From: Martin Schwidefsky Date: Mon, 1 Oct 2007 01:20:13 -0700 Subject: [PATCH] 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 Acked-by: Ingo Molnar Acked-by: Thomas Gleixner Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- kernel/futex.c | 26 ++++++++++++++++---------- kernel/futex_compat.c | 28 ++++++++++++++++++---------- 2 files changed, 34 insertions(+), 20 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 @@ -1965,11 +1966,13 @@ 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, diff --git a/kernel/futex_compat.c b/kernel/futex_compat.c index 7e52eb051f22..2c2e2954b713 100644 --- a/kernel/futex_compat.c +++ b/kernel/futex_compat.c @@ -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) { 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 @@ -61,10 +62,15 @@ void compat_exit_robust_list(struct task_struct *curr) 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_struct *curr) 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_struct *curr) cond_resched(); } + if (pending) + handle_futex_death((void __user *)pending + futex_offset, + curr, pip); } asmlinkage long -- 2.20.1