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seccomp: Report number of loaded filters in /proc/$pid/status

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A common question asked when debugging seccomp filters is "how many
filters are attached to your process?" Provide a way to easily answer
this question through /proc/$pid/status with a "Seccomp_filters" line.

Signed-off-by: Kees Cook <keescook@chromium.org>
This commit is contained in:
Kees Cook 2020-05-13 14:11:26 -07:00
parent e4d05028a0
commit c818c03b66
4 changed files with 10 additions and 0 deletions
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2
fs/proc/array.c
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@ -341,6 +341,8 @@ static inline void task_seccomp(struct seq_file *m, struct task_struct *p)
seq_put_decimal_ull(m, "NoNewPrivs:\t", task_no_new_privs(p));
#ifdef CONFIG_SECCOMP
seq_put_decimal_ull(m, "\nSeccomp:\t", p->seccomp.mode);
seq_put_decimal_ull(m, "\nSeccomp_filters:\t",
atomic_read(&p->seccomp.filter_count));
#endif
seq_puts(m, "\nSpeculation_Store_Bypass:\t");
switch (arch_prctl_spec_ctrl_get(p, PR_SPEC_STORE_BYPASS)) {

2
include/linux/seccomp.h
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@ -13,6 +13,7 @@
#ifdef CONFIG_SECCOMP
#include <linux/thread_info.h>
#include <linux/atomic.h>
#include <asm/seccomp.h>
struct seccomp_filter;
@ -29,6 +30,7 @@ struct seccomp_filter;
*/
struct seccomp {
int mode;
atomic_t filter_count;
struct seccomp_filter *filter;
};

3
init/init_task.c
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@ -204,6 +204,9 @@ struct task_struct init_task
#ifdef CONFIG_SECURITY
.security = NULL,
#endif
#ifdef CONFIG_SECCOMP
.seccomp = { .filter_count = ATOMIC_INIT(0) },
#endif
};
EXPORT_SYMBOL(init_task);

3
kernel/seccomp.c
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@ -398,6 +398,8 @@ static inline void seccomp_sync_threads(unsigned long flags)
put_seccomp_filter(thread);
smp_store_release(&thread->seccomp.filter,
caller->seccomp.filter);
atomic_set(&thread->seccomp.filter_count,
atomic_read(&thread->seccomp.filter_count));
/*
* Don't let an unprivileged task work around
@ -544,6 +546,7 @@ static long seccomp_attach_filter(unsigned int flags,
*/
filter->prev = current->seccomp.filter;
current->seccomp.filter = filter;
atomic_inc(&current->seccomp.filter_count);
/* Now that the new filter is in place, synchronize to all threads. */
if (flags & SECCOMP_FILTER_FLAG_TSYNC)