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author | Joel Fernandes (Google) <joel@joelfernandes.org> | 2019-07-16 16:30:06 -0700 |
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committer | Linus Torvalds <torvalds@linux-foundation.org> | 2019-07-16 19:23:24 -0700 |
commit | f57e515a1b56325a28a0972c632a623a9c84590c (patch) | |
tree | 62ec1f15fb12f43288b4246780642fbfa9c1c025 /kernel/pid.c | |
parent | 156e0b1a8112b76e351684ac948c59757037ac36 (diff) | |
download | linux-f57e515a1b56325a28a0972c632a623a9c84590c.tar.gz |
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>
Diffstat (limited to 'kernel/pid.c')
-rw-r--r-- | kernel/pid.c | 9 |
1 files changed, 4 insertions, 5 deletions
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]); |