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.
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Signed-off-by: Joel Fernandes (Google) <[email protected]>
---
Only change from v1->v2 is to get rid of the atomic_read().
include/linux/pid.h | 5 +++--
kernel/pid.c | 7 +++----
2 files changed, 6 insertions(+), 6 deletions(-)
diff --git a/include/linux/pid.h b/include/linux/pid.h
index 14a9a39da9c7..8cb86d377ff5 100644
--- a/include/linux/pid.h
+++ b/include/linux/pid.h
@@ -3,6 +3,7 @@
#define _LINUX_PID_H
#include <linux/rculist.h>
+#include <linux/refcount.h>
enum pid_type
{
@@ -56,7 +57,7 @@ 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];
@@ -69,7 +70,7 @@ extern struct pid init_struct_pid;
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 20881598bdfa..89c4849fab5d 100644
--- a/kernel/pid.c
+++ b/kernel/pid.c
@@ -37,7 +37,7 @@
#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/sched/task.h>
#include <linux/idr.h>
@@ -106,8 +106,7 @@ 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);
}
@@ -210,7 +209,7 @@ 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]);
--
2.22.0.410.gd8fdbe21b5-goog
On Fri, Jun 28, 2019 at 03:34:42PM -0400, Joel Fernandes (Google) wrote:
> 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.
>
> Cc: [email protected]
> Cc: [email protected]
> Cc: [email protected]
> Cc: [email protected]
> Cc: [email protected]
> Cc: [email protected]
> Cc: [email protected]
> Cc: [email protected]
> Cc: [email protected]
> Signed-off-by: Joel Fernandes (Google) <[email protected]>
Reviewed-by: Kees Cook <[email protected]>
-Kees
>
> ---
> Only change from v1->v2 is to get rid of the atomic_read().
>
> include/linux/pid.h | 5 +++--
> kernel/pid.c | 7 +++----
> 2 files changed, 6 insertions(+), 6 deletions(-)
>
> diff --git a/include/linux/pid.h b/include/linux/pid.h
> index 14a9a39da9c7..8cb86d377ff5 100644
> --- a/include/linux/pid.h
> +++ b/include/linux/pid.h
> @@ -3,6 +3,7 @@
> #define _LINUX_PID_H
>
> #include <linux/rculist.h>
> +#include <linux/refcount.h>
>
> enum pid_type
> {
> @@ -56,7 +57,7 @@ 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];
> @@ -69,7 +70,7 @@ extern struct pid init_struct_pid;
> 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 20881598bdfa..89c4849fab5d 100644
> --- a/kernel/pid.c
> +++ b/kernel/pid.c
> @@ -37,7 +37,7 @@
> #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/sched/task.h>
> #include <linux/idr.h>
>
> @@ -106,8 +106,7 @@ 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);
> }
> @@ -210,7 +209,7 @@ 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]);
>
> --
> 2.22.0.410.gd8fdbe21b5-goog
--
Kees Cook
On Fri, Jun 28, 2019 at 9:35 PM Joel Fernandes (Google)
<[email protected]> wrote:
> 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.
[...]
> struct pid
> {
> - atomic_t count;
> + refcount_t count;
[...]
> diff --git a/kernel/pid.c b/kernel/pid.c
> index 20881598bdfa..89c4849fab5d 100644
> --- a/kernel/pid.c
> +++ b/kernel/pid.c
> @@ -37,7 +37,7 @@
> #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/sched/task.h>
> #include <linux/idr.h>
>
> @@ -106,8 +106,7 @@ void put_pid(struct pid *pid)
init_struct_pid is defined as follows:
struct pid init_struct_pid = {
.count = ATOMIC_INIT(1),
[...]
};
This should be changed to REFCOUNT_INIT(1).
You should have received a compiler warning about this; I get the
following when trying to build with your patch applied:
jannh@jannh2:~/git/foreign/linux$ make kernel/pid.o
CALL scripts/checksyscalls.sh
CALL scripts/atomic/check-atomics.sh
DESCEND objtool
CC kernel/pid.o
kernel/pid.c:44:30: warning: missing braces around initializer
[-Wmissing-braces]
struct pid init_struct_pid = {
^
kernel/pid.c:44:30: warning: missing braces around initializer
[-Wmissing-braces]
kernel/pid.c:44:30: warning: missing braces around initializer
[-Wmissing-braces]
kernel/pid.c:44:30: warning: missing braces around initializer
[-Wmissing-braces]
kernel/pid.c:44:30: warning: missing braces around initializer
[-Wmissing-braces]
On Mon, Jul 01, 2019 at 07:48:26PM +0200, Jann Horn wrote:
> On Fri, Jun 28, 2019 at 9:35 PM Joel Fernandes (Google)
> <[email protected]> wrote:
> > 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.
> [...]
> > struct pid
> > {
> > - atomic_t count;
> > + refcount_t count;
> [...]
> > diff --git a/kernel/pid.c b/kernel/pid.c
> > index 20881598bdfa..89c4849fab5d 100644
> > --- a/kernel/pid.c
> > +++ b/kernel/pid.c
> > @@ -37,7 +37,7 @@
> > #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/sched/task.h>
> > #include <linux/idr.h>
> >
> > @@ -106,8 +106,7 @@ void put_pid(struct pid *pid)
>
> init_struct_pid is defined as follows:
>
> struct pid init_struct_pid = {
> .count = ATOMIC_INIT(1),
> [...]
> };
>
> This should be changed to REFCOUNT_INIT(1).
>
> You should have received a compiler warning about this; I get the
> following when trying to build with your patch applied:
Thanks. Andrew had fixed this in patch v1 but Linus dropped it for other
reasons. Anyway, I should have fixed this in my resubmit.
Sorry, I'll fix and resend!
- Joel
Hi "Joel,
Thank you for the patch! Perhaps something to improve:
[auto build test WARNING on linus/master]
[also build test WARNING on v5.2-rc6]
[cannot apply to next-20190625]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]
url: https://github.com/0day-ci/linux/commits/Joel-Fernandes-Google/Convert-struct-pid-count-to-refcount_t/20190702-003517
config: riscv-allnoconfig (attached as .config)
compiler: riscv64-linux-gcc (GCC) 7.4.0
reproduce:
wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
chmod +x ~/bin/make.cross
# save the attached .config to linux build tree
GCC_VERSION=7.4.0 make.cross ARCH=riscv
If you fix the issue, kindly add following tag
Reported-by: kbuild test robot <[email protected]>
All warnings (new ones prefixed by >>):
>> kernel/pid.c:44:30: warning: missing braces around initializer [-Wmissing-braces]
struct pid init_struct_pid = {
^
>> kernel/pid.c:44:30: warning: missing braces around initializer [-Wmissing-braces]
>> kernel/pid.c:44:30: warning: missing braces around initializer [-Wmissing-braces]
>> kernel/pid.c:44:30: warning: missing braces around initializer [-Wmissing-braces]
>> kernel/pid.c:44:30: warning: missing braces around initializer [-Wmissing-braces]
vim +44 kernel/pid.c
^1da177e Linus Torvalds 2005-04-16 43
e1e871af David Howells 2018-01-02 @44 struct pid init_struct_pid = {
e1e871af David Howells 2018-01-02 45 .count = ATOMIC_INIT(1),
e1e871af David Howells 2018-01-02 46 .tasks = {
e1e871af David Howells 2018-01-02 47 { .first = NULL },
e1e871af David Howells 2018-01-02 48 { .first = NULL },
e1e871af David Howells 2018-01-02 49 { .first = NULL },
e1e871af David Howells 2018-01-02 50 },
e1e871af David Howells 2018-01-02 51 .level = 0,
e1e871af David Howells 2018-01-02 52 .numbers = { {
e1e871af David Howells 2018-01-02 53 .nr = 0,
e1e871af David Howells 2018-01-02 54 .ns = &init_pid_ns,
e1e871af David Howells 2018-01-02 55 }, }
e1e871af David Howells 2018-01-02 56 };
^1da177e Linus Torvalds 2005-04-16 57
:::::: The code at line 44 was first introduced by commit
:::::: e1e871aff3ded26348c631b1370e257d401cd22d Expand INIT_STRUCT_PID and remove
:::::: TO: David Howells <[email protected]>
:::::: CC: David Howells <[email protected]>
---
0-DAY kernel test infrastructure Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all Intel Corporation
On Mon, Jul 1, 2019 at 2:47 PM kbuild test robot <[email protected]> wrote:
>
> Hi "Joel,
>
> Thank you for the patch! Perhaps something to improve:
>
> [auto build test WARNING on linus/master]
> [also build test WARNING on v5.2-rc6]
> [cannot apply to next-20190625]
> [if your patch is applied to the wrong git tree, please drop us a note to help improve the system]
Jann H was faster than the robot in catching this, so humanity still has hope!
Its fixed in v3.