diff options
author | Joel Fernandes (Google) <joel@joelfernandes.org> | 2019-07-17 02:30:06 +0300 |
---|---|---|
committer | Linus Torvalds <torvalds@linux-foundation.org> | 2019-07-17 05:23:24 +0300 |
commit | f57e515a1b56325a28a0972c632a623a9c84590c (patch) | |
tree | 62ec1f15fb12f43288b4246780642fbfa9c1c025 | |
parent | 156e0b1a8112b76e351684ac948c59757037ac36 (diff) | |
download | linux-f57e515a1b56325a28a0972c632a623a9c84590c.tar.xz |
kernel/pid.c: convert struct pid count to refcount_t
struct pid's count is an atomic_t field used as a refcount. Use
refcount_t for it which is basically atomic_t but does additional
checking to prevent use-after-free bugs.
For memory ordering, the only change is with the following:
- if ((atomic_read(&pid->count) == 1) ||
- atomic_dec_and_test(&pid->count)) {
+ if (refcount_dec_and_test(&pid->count)) {
kmem_cache_free(ns->pid_cachep, pid);
Here the change is from: Fully ordered --> RELEASE + ACQUIRE (as per
refcount-vs-atomic.rst) This ACQUIRE should take care of making sure the
free happens after the refcount_dec_and_test().
The above hunk also removes atomic_read() since it is not needed for the
code to work and it is unclear how beneficial it is. The removal lets
refcount_dec_and_test() check for cases where get_pid() happened before
the object was freed.
Link: http://lkml.kernel.org/r/20190701183826.191936-1-joel@joelfernandes.org
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Reviewed-by: Andrea Parri <andrea.parri@amarulasolutions.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Elena Reshetova <elena.reshetova@intel.com>
Cc: Jann Horn <jannh@google.com>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: KJ Tsanaktsidis <ktsanaktsidis@zendesk.com>
Cc: Michal Hocko <mhocko@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r-- | include/linux/pid.h | 5 | ||||
-rw-r--r-- | kernel/pid.c | 9 |
2 files changed, 7 insertions, 7 deletions
diff --git a/include/linux/pid.h b/include/linux/pid.h index 1484db6ca8d1..2a83e434db9d 100644 --- a/include/linux/pid.h +++ b/include/linux/pid.h @@ -4,6 +4,7 @@ #include <linux/rculist.h> #include <linux/wait.h> +#include <linux/refcount.h> enum pid_type { @@ -57,7 +58,7 @@ struct upid { struct pid { - atomic_t count; + refcount_t count; unsigned int level; /* lists of tasks that use this pid */ struct hlist_head tasks[PIDTYPE_MAX]; @@ -74,7 +75,7 @@ extern const struct file_operations pidfd_fops; static inline struct pid *get_pid(struct pid *pid) { if (pid) - atomic_inc(&pid->count); + refcount_inc(&pid->count); return pid; } diff --git a/kernel/pid.c b/kernel/pid.c index 16263b526560..0a9f2e437217 100644 --- a/kernel/pid.c +++ b/kernel/pid.c @@ -37,14 +37,14 @@ #include <linux/init_task.h> #include <linux/syscalls.h> #include <linux/proc_ns.h> -#include <linux/proc_fs.h> +#include <linux/refcount.h> #include <linux/anon_inodes.h> #include <linux/sched/signal.h> #include <linux/sched/task.h> #include <linux/idr.h> struct pid init_struct_pid = { - .count = ATOMIC_INIT(1), + .count = REFCOUNT_INIT(1), .tasks = { { .first = NULL }, { .first = NULL }, @@ -108,8 +108,7 @@ void put_pid(struct pid *pid) return; ns = pid->numbers[pid->level].ns; - if ((atomic_read(&pid->count) == 1) || - atomic_dec_and_test(&pid->count)) { + if (refcount_dec_and_test(&pid->count)) { kmem_cache_free(ns->pid_cachep, pid); put_pid_ns(ns); } @@ -212,7 +211,7 @@ struct pid *alloc_pid(struct pid_namespace *ns) } get_pid_ns(ns); - atomic_set(&pid->count, 1); + refcount_set(&pid->count, 1); for (type = 0; type < PIDTYPE_MAX; ++type) INIT_HLIST_HEAD(&pid->tasks[type]); |