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seccomp: fix the usage of get/put_seccomp_filter() in seccomp_get_filter()

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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seccomp.filter to have been replaced by SECCOMP_FILTER_FLAG_TSYNC.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: f8e529ed941b ("seccomp, ptrace: add support for dumping seccomp filters")
Reported-by: Chris Salls <chrissalls5@gmail.com>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
[tycho: add __get_seccomp_filter vs. open coding refcount_inc()]
Signed-off-by: Tycho Andersen <tycho@docker.com>
[kees: tweak commit log]
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Oleg Nesterov 2017-09-27 09:25:30 -06:00 committed by Greg Kroah-Hartman
parent 668cee82cd
commit 9237605e0b
1 changed files with 16 additions and 7 deletions
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23
kernel/seccomp.c
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@ -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
@ -927,13 +936,13 @@ 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: