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timerfd: Protect the might cancel mechanism proper

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The handling of the might_cancel queueing is not properly protected, so
parallel operations on the file descriptor can race with each other and
lead to list corruptions or use after free.

Protect the context for these operations with a seperate lock.

The wait queue lock cannot be reused for this because that would create a
lock inversion scenario vs. the cancel lock. Replacing might_cancel with an
atomic (atomic_t or atomic bit) does not help either because it still can
race vs. the actual list operation.

Change-Id: Ib0fc09f70b40be38badbbf674aacaa5c24a466b7
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: "linux-fsdevel@vger.kernel.org"
Cc: syzkaller <syzkaller@googlegroups.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: linux-fsdevel@vger.kernel.org
Link: http://lkml.kernel.org/r/alpine.DEB.2.20.1701311521430.3457@nanos
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Git-repo: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git
Git-commit: 1e38da300e1e395a15048b0af1e5305bd91402f6
Signed-off-by: Dennis Cagle <dcagle@codeaurora.org>
This commit is contained in:
Thomas Gleixner 2017-01-31 15:24:03 +01:00 committed by Gerrit - the friendly Code Review server
parent 2eaf14b921
commit 614161ac1a
1 changed files with 14 additions and 3 deletions
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17
fs/timerfd.c
View file

@ -39,6 +39,7 @@ struct timerfd_ctx {
int clockid;
struct rcu_head rcu;
struct list_head clist;
spinlock_t cancel_lock;
bool might_cancel;
};
@ -112,7 +113,7 @@ void timerfd_clock_was_set(void)
rcu_read_unlock();
}
static void timerfd_remove_cancel(struct timerfd_ctx *ctx)
static void __timerfd_remove_cancel(struct timerfd_ctx *ctx)
{
if (ctx->might_cancel) {
ctx->might_cancel = false;
@ -122,6 +123,13 @@ static void timerfd_remove_cancel(struct timerfd_ctx *ctx)
}
}
static void timerfd_remove_cancel(struct timerfd_ctx *ctx)
{
spin_lock(&ctx->cancel_lock);
__timerfd_remove_cancel(ctx);
spin_unlock(&ctx->cancel_lock);
}
static bool timerfd_canceled(struct timerfd_ctx *ctx)
{
if (!ctx->might_cancel || ctx->moffs.tv64 != KTIME_MAX)
@ -132,6 +140,7 @@ static bool timerfd_canceled(struct timerfd_ctx *ctx)
static void timerfd_setup_cancel(struct timerfd_ctx *ctx, int flags)
{
spin_lock(&ctx->cancel_lock);
if ((ctx->clockid == CLOCK_REALTIME ||
ctx->clockid == CLOCK_REALTIME_ALARM ||
ctx->clockid == CLOCK_POWEROFF_ALARM) &&
@ -142,9 +151,10 @@ static void timerfd_setup_cancel(struct timerfd_ctx *ctx, int flags)
list_add_rcu(&ctx->clist, &cancel_list);
spin_unlock(&cancel_lock);
}
} else if (ctx->might_cancel) {
timerfd_remove_cancel(ctx);
} else {
__timerfd_remove_cancel(ctx);
}
spin_unlock(&ctx->cancel_lock);
}
static ktime_t timerfd_get_remaining(struct timerfd_ctx *ctx)
@ -329,6 +339,7 @@ SYSCALL_DEFINE2(timerfd_create, int, clockid, int, flags)
return -ENOMEM;
init_waitqueue_head(&ctx->wqh);
spin_lock_init(&ctx->cancel_lock);
ctx->clockid = clockid;
if (isalarm(ctx)) {