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Commit be69c4c0 authored by Oleg Nesterov's avatar Oleg Nesterov Committed by Greg Kroah-Hartman
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seccomp: fix the usage of get/put_seccomp_filter() in seccomp_get_filter() 



commit 66a733ea6b611aecf0119514d2dddab5f9d6c01e upstream.

As Chris explains, get_seccomp_filter() and put_seccomp_filter() can end
up using different filters. Once we drop ->siglock it is possible for
task->seccomp.filter to have been replaced by SECCOMP_FILTER_FLAG_TSYNC.

Fixes: f8e529ed ("seccomp, ptrace: add support for dumping seccomp filters")
Reported-by: default avatarChris Salls <chrissalls5@gmail.com>
Signed-off-by: default avatarOleg Nesterov <oleg@redhat.com>
[tycho: add __get_seccomp_filter vs. open coding refcount_inc()]
Signed-off-by: default avatarTycho Andersen <tycho@docker.com>
[kees: tweak commit log]
Signed-off-by: default avatarKees Cook <keescook@chromium.org>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 58052a74

kernel/seccomp.c

+16 −7
Original line number Diff line number Diff line
@@ -457,14 +457,19 @@ static long seccomp_attach_filter(unsigned int flags, 
	return 0;

}



void __get_seccomp_filter(struct seccomp_filter *filter)

{

	/* Reference count is bounded by the number of total processes. */

	atomic_inc(&filter->usage);

}



/* get_seccomp_filter - increments the reference count of the filter on @tsk */

void get_seccomp_filter(struct task_struct *tsk)

{

	struct seccomp_filter *orig = tsk->seccomp.filter;

	if (!orig)

		return;

	/* Reference count is bounded by the number of total processes. */

	atomic_inc(&orig->usage);

	__get_seccomp_filter(orig);

}



static inline void seccomp_filter_free(struct seccomp_filter *filter)
@@ -475,10 +480,8 @@ static inline void seccomp_filter_free(struct seccomp_filter *filter) 
	}

}



/* put_seccomp_filter - decrements the ref count of tsk->seccomp.filter */

void put_seccomp_filter(struct task_struct *tsk)

static void __put_seccomp_filter(struct seccomp_filter *orig)

{

	struct seccomp_filter *orig = tsk->seccomp.filter;

	/* Clean up single-reference branches iteratively. */

	while (orig && atomic_dec_and_test(&orig->usage)) {

		struct seccomp_filter *freeme = orig;
@@ -487,6 +490,12 @@ void put_seccomp_filter(struct task_struct *tsk) 
	}

}



/* put_seccomp_filter - decrements the ref count of tsk->seccomp.filter */

void put_seccomp_filter(struct task_struct *tsk)

{

	__put_seccomp_filter(tsk->seccomp.filter);

}



/**

 * seccomp_send_sigsys - signals the task to allow in-process syscall emulation

 * @syscall: syscall number to send to userland
@@ -892,13 +901,13 @@ long seccomp_get_filter(struct task_struct *task, unsigned long filter_off, 
	if (!data)

		goto out;



	get_seccomp_filter(task);

	__get_seccomp_filter(filter);

	spin_unlock_irq(&task->sighand->siglock);



	if (copy_to_user(data, fprog->filter, bpf_classic_proglen(fprog)))

		ret = -EFAULT;



	put_seccomp_filter(task);

	__put_seccomp_filter(filter);

	return ret;



out: