There's a possible race in perf_mmap_close when checking ring buffer's
mmap_count refcount value. The problem is that the mmap_count check is
not atomic because we call atomic_dec and atomic_read separately.
perf_mmap_close:
...
atomic_dec(&rb->mmap_count);
...
if (atomic_read(&rb->mmap_count))
goto out_put;
<ring buffer detach>
free_uid
out_put:
ring_buffer_put(rb); /* could be last */
The race can happen when we have two (or more) events sharing same ring
buffer and they go through atomic_dec and then they both see 0 as refcount
value later in atomic_read. Then both will go on and execute code which
is meant to be run just once.
The code that detaches ring buffer is probably fine to be executed more
than once, but the problem is in calling free_uid, which will later on
demonstrate in related crashes and refcount warnings, like:
refcount_t: addition on 0; use-after-free.
...
RIP: 0010:refcount_warn_saturate+0x6d/0xf
...
Call Trace:
prepare_creds+0x190/0x1e0
copy_creds+0x35/0x172
copy_process+0x471/0x1a80
_do_fork+0x83/0x3a0
__do_sys_wait4+0x83/0x90
__do_sys_clone+0x85/0xa0
do_syscall_64+0x5b/0x1e0
entry_SYSCALL_64_after_hwframe+0x44/0xa9
Using atomic decrease and check instead of separated calls.
This fixes CVE-2020-14351.
Signed-off-by: Jiri Olsa <[email protected]>
---
kernel/events/core.c | 4 +---
1 file changed, 1 insertion(+), 3 deletions(-)
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 7ed5248f0445..29313cc54d9e 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -5903,8 +5903,6 @@ static void perf_mmap_close(struct vm_area_struct *vma)
mutex_unlock(&event->mmap_mutex);
}
- atomic_dec(&rb->mmap_count);
-
if (!atomic_dec_and_mutex_lock(&event->mmap_count, &event->mmap_mutex))
goto out_put;
@@ -5912,7 +5910,7 @@ static void perf_mmap_close(struct vm_area_struct *vma)
mutex_unlock(&event->mmap_mutex);
/* If there's still other mmap()s of this buffer, we're done. */
- if (atomic_read(&rb->mmap_count))
+ if (!atomic_dec_and_test(&rb->mmap_count))
goto out_put;
/*
--
2.26.2
On Thu, Sep 10, 2020 at 7:42 PM Jiri Olsa <[email protected]> wrote:
>
> There's a possible race in perf_mmap_close when checking ring buffer's
> mmap_count refcount value. The problem is that the mmap_count check is
> not atomic because we call atomic_dec and atomic_read separately.
>
> perf_mmap_close:
> ...
> atomic_dec(&rb->mmap_count);
> ...
> if (atomic_read(&rb->mmap_count))
> goto out_put;
>
> <ring buffer detach>
> free_uid
>
> out_put:
> ring_buffer_put(rb); /* could be last */
>
> The race can happen when we have two (or more) events sharing same ring
> buffer and they go through atomic_dec and then they both see 0 as refcount
> value later in atomic_read. Then both will go on and execute code which
> is meant to be run just once.
>
> The code that detaches ring buffer is probably fine to be executed more
> than once, but the problem is in calling free_uid, which will later on
> demonstrate in related crashes and refcount warnings, like:
>
> refcount_t: addition on 0; use-after-free.
> ...
> RIP: 0010:refcount_warn_saturate+0x6d/0xf
> ...
> Call Trace:
> prepare_creds+0x190/0x1e0
> copy_creds+0x35/0x172
> copy_process+0x471/0x1a80
> _do_fork+0x83/0x3a0
> __do_sys_wait4+0x83/0x90
> __do_sys_clone+0x85/0xa0
> do_syscall_64+0x5b/0x1e0
> entry_SYSCALL_64_after_hwframe+0x44/0xa9
>
> Using atomic decrease and check instead of separated calls.
> This fixes CVE-2020-14351.
>
> Signed-off-by: Jiri Olsa <[email protected]>
> ---
> kernel/events/core.c | 4 +---
> 1 file changed, 1 insertion(+), 3 deletions(-)
>
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 7ed5248f0445..29313cc54d9e 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -5903,8 +5903,6 @@ static void perf_mmap_close(struct vm_area_struct *vma)
> mutex_unlock(&event->mmap_mutex);
> }
>
> - atomic_dec(&rb->mmap_count);
> -
> if (!atomic_dec_and_mutex_lock(&event->mmap_count, &event->mmap_mutex))
> goto out_put;
But when it takes the goto, rb->mmap_count won't decrement anymore..
Thanks
Namhyung
>
> @@ -5912,7 +5910,7 @@ static void perf_mmap_close(struct vm_area_struct *vma)
> mutex_unlock(&event->mmap_mutex);
>
> /* If there's still other mmap()s of this buffer, we're done. */
> - if (atomic_read(&rb->mmap_count))
> + if (!atomic_dec_and_test(&rb->mmap_count))
> goto out_put;
>
> /*
> --
> 2.26.2
>
On Thu, Sep 10, 2020 at 10:48:02PM +0900, Namhyung Kim wrote:
SNIP
> > _do_fork+0x83/0x3a0
> > __do_sys_wait4+0x83/0x90
> > __do_sys_clone+0x85/0xa0
> > do_syscall_64+0x5b/0x1e0
> > entry_SYSCALL_64_after_hwframe+0x44/0xa9
> >
> > Using atomic decrease and check instead of separated calls.
> > This fixes CVE-2020-14351.
> >
> > Signed-off-by: Jiri Olsa <[email protected]>
> > ---
> > kernel/events/core.c | 4 +---
> > 1 file changed, 1 insertion(+), 3 deletions(-)
> >
> > diff --git a/kernel/events/core.c b/kernel/events/core.c
> > index 7ed5248f0445..29313cc54d9e 100644
> > --- a/kernel/events/core.c
> > +++ b/kernel/events/core.c
> > @@ -5903,8 +5903,6 @@ static void perf_mmap_close(struct vm_area_struct *vma)
> > mutex_unlock(&event->mmap_mutex);
> > }
> >
> > - atomic_dec(&rb->mmap_count);
> > -
> > if (!atomic_dec_and_mutex_lock(&event->mmap_count, &event->mmap_mutex))
> > goto out_put;
>
> But when it takes the goto, rb->mmap_count won't decrement anymore..
event->mmap_count is per event, so if we have have race in here,
2 threads can go through with each event->mmap_count reaching zero
jirka
Hi Jiri,
On Thu, Sep 10, 2020 at 11:50 PM Jiri Olsa <[email protected]> wrote:
>
> On Thu, Sep 10, 2020 at 10:48:02PM +0900, Namhyung Kim wrote:
>
> SNIP
>
> > > _do_fork+0x83/0x3a0
> > > __do_sys_wait4+0x83/0x90
> > > __do_sys_clone+0x85/0xa0
> > > do_syscall_64+0x5b/0x1e0
> > > entry_SYSCALL_64_after_hwframe+0x44/0xa9
> > >
> > > Using atomic decrease and check instead of separated calls.
> > > This fixes CVE-2020-14351.
> > >
> > > Signed-off-by: Jiri Olsa <[email protected]>
> > > ---
> > > kernel/events/core.c | 4 +---
> > > 1 file changed, 1 insertion(+), 3 deletions(-)
> > >
> > > diff --git a/kernel/events/core.c b/kernel/events/core.c
> > > index 7ed5248f0445..29313cc54d9e 100644
> > > --- a/kernel/events/core.c
> > > +++ b/kernel/events/core.c
> > > @@ -5903,8 +5903,6 @@ static void perf_mmap_close(struct vm_area_struct *vma)
> > > mutex_unlock(&event->mmap_mutex);
> > > }
> > >
> > > - atomic_dec(&rb->mmap_count);
> > > -
> > > if (!atomic_dec_and_mutex_lock(&event->mmap_count, &event->mmap_mutex))
> > > goto out_put;
> >
> > But when it takes the goto, rb->mmap_count won't decrement anymore..
>
> event->mmap_count is per event, so if we have have race in here,
> 2 threads can go through with each event->mmap_count reaching zero
Maybe I'm missing something.
But as far as I can see, perf_mmap_close() always decremented both
rb->mmap_count and event->mmap_count. But with this change,
it seems not decrement rb->mmap_count when event->mmap_count
doesn't go to zero, right?
Thanks
Namhyung
On Fri, Sep 11, 2020 at 12:05:10PM +0900, Namhyung Kim wrote:
> Hi Jiri,
>
> On Thu, Sep 10, 2020 at 11:50 PM Jiri Olsa <[email protected]> wrote:
> >
> > On Thu, Sep 10, 2020 at 10:48:02PM +0900, Namhyung Kim wrote:
> >
> > SNIP
> >
> > > > _do_fork+0x83/0x3a0
> > > > __do_sys_wait4+0x83/0x90
> > > > __do_sys_clone+0x85/0xa0
> > > > do_syscall_64+0x5b/0x1e0
> > > > entry_SYSCALL_64_after_hwframe+0x44/0xa9
> > > >
> > > > Using atomic decrease and check instead of separated calls.
> > > > This fixes CVE-2020-14351.
> > > >
> > > > Signed-off-by: Jiri Olsa <[email protected]>
> > > > ---
> > > > kernel/events/core.c | 4 +---
> > > > 1 file changed, 1 insertion(+), 3 deletions(-)
> > > >
> > > > diff --git a/kernel/events/core.c b/kernel/events/core.c
> > > > index 7ed5248f0445..29313cc54d9e 100644
> > > > --- a/kernel/events/core.c
> > > > +++ b/kernel/events/core.c
> > > > @@ -5903,8 +5903,6 @@ static void perf_mmap_close(struct vm_area_struct *vma)
> > > > mutex_unlock(&event->mmap_mutex);
> > > > }
> > > >
> > > > - atomic_dec(&rb->mmap_count);
> > > > -
> > > > if (!atomic_dec_and_mutex_lock(&event->mmap_count, &event->mmap_mutex))
> > > > goto out_put;
> > >
> > > But when it takes the goto, rb->mmap_count won't decrement anymore..
> >
> > event->mmap_count is per event, so if we have have race in here,
> > 2 threads can go through with each event->mmap_count reaching zero
>
> Maybe I'm missing something.
>
> But as far as I can see, perf_mmap_close() always decremented both
> rb->mmap_count and event->mmap_count. But with this change,
> it seems not decrement rb->mmap_count when event->mmap_count
> doesn't go to zero, right?
ugh, that's right.. how about change below
jirka
---
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 7ed5248f0445..8ab2400aef55 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -5868,11 +5868,11 @@ static void perf_pmu_output_stop(struct perf_event *event);
static void perf_mmap_close(struct vm_area_struct *vma)
{
struct perf_event *event = vma->vm_file->private_data;
-
struct perf_buffer *rb = ring_buffer_get(event);
struct user_struct *mmap_user = rb->mmap_user;
int mmap_locked = rb->mmap_locked;
unsigned long size = perf_data_size(rb);
+ bool detach_rest = false;
if (event->pmu->event_unmapped)
event->pmu->event_unmapped(event, vma->vm_mm);
@@ -5903,7 +5903,8 @@ static void perf_mmap_close(struct vm_area_struct *vma)
mutex_unlock(&event->mmap_mutex);
}
- atomic_dec(&rb->mmap_count);
+ if (atomic_dec_and_test(&rb->mmap_count))
+ detach_rest = true;
if (!atomic_dec_and_mutex_lock(&event->mmap_count, &event->mmap_mutex))
goto out_put;
@@ -5912,7 +5913,7 @@ static void perf_mmap_close(struct vm_area_struct *vma)
mutex_unlock(&event->mmap_mutex);
/* If there's still other mmap()s of this buffer, we're done. */
- if (atomic_read(&rb->mmap_count))
+ if (!detach_rest)
goto out_put;
/*
On Fri, Sep 11, 2020 at 4:49 PM Jiri Olsa <[email protected]> wrote:
> ugh, that's right.. how about change below
Acked-by: Namhyung Kim <[email protected]>
Thanks
Namhyung
>
> jirka
>
>
> ---
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 7ed5248f0445..8ab2400aef55 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -5868,11 +5868,11 @@ static void perf_pmu_output_stop(struct perf_event *event);
> static void perf_mmap_close(struct vm_area_struct *vma)
> {
> struct perf_event *event = vma->vm_file->private_data;
> -
> struct perf_buffer *rb = ring_buffer_get(event);
> struct user_struct *mmap_user = rb->mmap_user;
> int mmap_locked = rb->mmap_locked;
> unsigned long size = perf_data_size(rb);
> + bool detach_rest = false;
>
> if (event->pmu->event_unmapped)
> event->pmu->event_unmapped(event, vma->vm_mm);
> @@ -5903,7 +5903,8 @@ static void perf_mmap_close(struct vm_area_struct *vma)
> mutex_unlock(&event->mmap_mutex);
> }
>
> - atomic_dec(&rb->mmap_count);
> + if (atomic_dec_and_test(&rb->mmap_count))
> + detach_rest = true;
>
> if (!atomic_dec_and_mutex_lock(&event->mmap_count, &event->mmap_mutex))
> goto out_put;
> @@ -5912,7 +5913,7 @@ static void perf_mmap_close(struct vm_area_struct *vma)
> mutex_unlock(&event->mmap_mutex);
>
> /* If there's still other mmap()s of this buffer, we're done. */
> - if (atomic_read(&rb->mmap_count))
> + if (!detach_rest)
> goto out_put;
>
> /*
>
On Mon, Sep 14, 2020 at 09:48:43PM +0900, Namhyung Kim wrote:
> On Fri, Sep 11, 2020 at 4:49 PM Jiri Olsa <[email protected]> wrote:
> > ugh, that's right.. how about change below
>
> Acked-by: Namhyung Kim <[email protected]>
thanks, I'll send full patch after we're done testing this
jirka
>
> Thanks
> Namhyung
>
>
> >
> > jirka
> >
> >
> > ---
> > diff --git a/kernel/events/core.c b/kernel/events/core.c
> > index 7ed5248f0445..8ab2400aef55 100644
> > --- a/kernel/events/core.c
> > +++ b/kernel/events/core.c
> > @@ -5868,11 +5868,11 @@ static void perf_pmu_output_stop(struct perf_event *event);
> > static void perf_mmap_close(struct vm_area_struct *vma)
> > {
> > struct perf_event *event = vma->vm_file->private_data;
> > -
> > struct perf_buffer *rb = ring_buffer_get(event);
> > struct user_struct *mmap_user = rb->mmap_user;
> > int mmap_locked = rb->mmap_locked;
> > unsigned long size = perf_data_size(rb);
> > + bool detach_rest = false;
> >
> > if (event->pmu->event_unmapped)
> > event->pmu->event_unmapped(event, vma->vm_mm);
> > @@ -5903,7 +5903,8 @@ static void perf_mmap_close(struct vm_area_struct *vma)
> > mutex_unlock(&event->mmap_mutex);
> > }
> >
> > - atomic_dec(&rb->mmap_count);
> > + if (atomic_dec_and_test(&rb->mmap_count))
> > + detach_rest = true;
> >
> > if (!atomic_dec_and_mutex_lock(&event->mmap_count, &event->mmap_mutex))
> > goto out_put;
> > @@ -5912,7 +5913,7 @@ static void perf_mmap_close(struct vm_area_struct *vma)
> > mutex_unlock(&event->mmap_mutex);
> >
> > /* If there's still other mmap()s of this buffer, we're done. */
> > - if (atomic_read(&rb->mmap_count))
> > + if (!detach_rest)
> > goto out_put;
> >
> > /*
> >
>
On Mon, 14 Sep 2020, Jiri Olsa wrote:
> On Mon, Sep 14, 2020 at 09:48:43PM +0900, Namhyung Kim wrote:
> > On Fri, Sep 11, 2020 at 4:49 PM Jiri Olsa <[email protected]> wrote:
> > > ugh, that's right.. how about change below
> >
> > Acked-by: Namhyung Kim <[email protected]>
>
> thanks, I'll send full patch after we're done testing this
>
> jirka
I've tested the change and seems OK to me.
Tested-by: Michael Petlan <[email protected]>
>
> >
> > Thanks
> > Namhyung
> >
> >
> > >
> > > jirka
> > >
> > >
> > > ---
> > > diff --git a/kernel/events/core.c b/kernel/events/core.c
> > > index 7ed5248f0445..8ab2400aef55 100644
> > > --- a/kernel/events/core.c
> > > +++ b/kernel/events/core.c
> > > @@ -5868,11 +5868,11 @@ static void perf_pmu_output_stop(struct perf_event *event);
> > > static void perf_mmap_close(struct vm_area_struct *vma)
> > > {
> > > struct perf_event *event = vma->vm_file->private_data;
> > > -
> > > struct perf_buffer *rb = ring_buffer_get(event);
> > > struct user_struct *mmap_user = rb->mmap_user;
> > > int mmap_locked = rb->mmap_locked;
> > > unsigned long size = perf_data_size(rb);
> > > + bool detach_rest = false;
> > >
> > > if (event->pmu->event_unmapped)
> > > event->pmu->event_unmapped(event, vma->vm_mm);
> > > @@ -5903,7 +5903,8 @@ static void perf_mmap_close(struct vm_area_struct *vma)
> > > mutex_unlock(&event->mmap_mutex);
> > > }
> > >
> > > - atomic_dec(&rb->mmap_count);
> > > + if (atomic_dec_and_test(&rb->mmap_count))
> > > + detach_rest = true;
> > >
> > > if (!atomic_dec_and_mutex_lock(&event->mmap_count, &event->mmap_mutex))
> > > goto out_put;
> > > @@ -5912,7 +5913,7 @@ static void perf_mmap_close(struct vm_area_struct *vma)
> > > mutex_unlock(&event->mmap_mutex);
> > >
> > > /* If there's still other mmap()s of this buffer, we're done. */
> > > - if (atomic_read(&rb->mmap_count))
> > > + if (!detach_rest)
> > > goto out_put;
> > >
> > > /*
> > >
> >
>
There's a possible race in perf_mmap_close when checking ring buffer's
mmap_count refcount value. The problem is that the mmap_count check is
not atomic because we call atomic_dec and atomic_read separately.
perf_mmap_close:
...
atomic_dec(&rb->mmap_count);
...
if (atomic_read(&rb->mmap_count))
goto out_put;
<ring buffer detach>
free_uid
out_put:
ring_buffer_put(rb); /* could be last */
The race can happen when we have two (or more) events sharing same ring
buffer and they go through atomic_dec and then they both see 0 as refcount
value later in atomic_read. Then both will go on and execute code which
is meant to be run just once.
The code that detaches ring buffer is probably fine to be executed more
than once, but the problem is in calling free_uid, which will later on
demonstrate in related crashes and refcount warnings, like:
refcount_t: addition on 0; use-after-free.
...
RIP: 0010:refcount_warn_saturate+0x6d/0xf
...
Call Trace:
prepare_creds+0x190/0x1e0
copy_creds+0x35/0x172
copy_process+0x471/0x1a80
_do_fork+0x83/0x3a0
__do_sys_wait4+0x83/0x90
__do_sys_clone+0x85/0xa0
do_syscall_64+0x5b/0x1e0
entry_SYSCALL_64_after_hwframe+0x44/0xa9
Using atomic decrease and check instead of separated calls.
This fixes CVE-2020-14351.
Acked-by: Namhyung Kim <[email protected]>
Tested-by: Michael Petlan <[email protected]>
Signed-off-by: Jiri Olsa <[email protected]>
---
kernel/events/core.c | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 7ed5248f0445..8ab2400aef55 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -5868,11 +5868,11 @@ static void perf_pmu_output_stop(struct perf_event *event);
static void perf_mmap_close(struct vm_area_struct *vma)
{
struct perf_event *event = vma->vm_file->private_data;
-
struct perf_buffer *rb = ring_buffer_get(event);
struct user_struct *mmap_user = rb->mmap_user;
int mmap_locked = rb->mmap_locked;
unsigned long size = perf_data_size(rb);
+ bool detach_rest = false;
if (event->pmu->event_unmapped)
event->pmu->event_unmapped(event, vma->vm_mm);
@@ -5903,7 +5903,8 @@ static void perf_mmap_close(struct vm_area_struct *vma)
mutex_unlock(&event->mmap_mutex);
}
- atomic_dec(&rb->mmap_count);
+ if (atomic_dec_and_test(&rb->mmap_count))
+ detach_rest = true;
if (!atomic_dec_and_mutex_lock(&event->mmap_count, &event->mmap_mutex))
goto out_put;
@@ -5912,7 +5913,7 @@ static void perf_mmap_close(struct vm_area_struct *vma)
mutex_unlock(&event->mmap_mutex);
/* If there's still other mmap()s of this buffer, we're done. */
- if (atomic_read(&rb->mmap_count))
+ if (!detach_rest)
goto out_put;
/*
--
2.26.2
On Wed, Sep 16, 2020 at 01:53:11PM +0200, Jiri Olsa wrote:
> There's a possible race in perf_mmap_close when checking ring buffer's
> mmap_count refcount value. The problem is that the mmap_count check is
> not atomic because we call atomic_dec and atomic_read separately.
>
> perf_mmap_close:
> ...
> atomic_dec(&rb->mmap_count);
> ...
> if (atomic_read(&rb->mmap_count))
> goto out_put;
>
> <ring buffer detach>
> free_uid
>
> out_put:
> ring_buffer_put(rb); /* could be last */
>
> The race can happen when we have two (or more) events sharing same ring
> buffer and they go through atomic_dec and then they both see 0 as refcount
> value later in atomic_read. Then both will go on and execute code which
> is meant to be run just once.
>
> The code that detaches ring buffer is probably fine to be executed more
> than once, but the problem is in calling free_uid, which will later on
> demonstrate in related crashes and refcount warnings, like:
>
> refcount_t: addition on 0; use-after-free.
> ...
> RIP: 0010:refcount_warn_saturate+0x6d/0xf
> ...
> Call Trace:
> prepare_creds+0x190/0x1e0
> copy_creds+0x35/0x172
> copy_process+0x471/0x1a80
> _do_fork+0x83/0x3a0
> __do_sys_wait4+0x83/0x90
> __do_sys_clone+0x85/0xa0
> do_syscall_64+0x5b/0x1e0
> entry_SYSCALL_64_after_hwframe+0x44/0xa9
>
> Using atomic decrease and check instead of separated calls.
> This fixes CVE-2020-14351.
I'm tempted to remove that line; I can never seem to find anything
useful in a CVE.
Fixes: ?
> Acked-by: Namhyung Kim <[email protected]>
> Tested-by: Michael Petlan <[email protected]>
> Signed-off-by: Jiri Olsa <[email protected]>
On Wed, Sep 16, 2020 at 01:53:11PM +0200, Jiri Olsa wrote:
> There's a possible race in perf_mmap_close when checking ring buffer's
> mmap_count refcount value. The problem is that the mmap_count check is
> not atomic because we call atomic_dec and atomic_read separately.
>
> perf_mmap_close:
> ...
> atomic_dec(&rb->mmap_count);
> ...
> if (atomic_read(&rb->mmap_count))
> goto out_put;
>
> <ring buffer detach>
> free_uid
>
> out_put:
> ring_buffer_put(rb); /* could be last */
>
> The race can happen when we have two (or more) events sharing same ring
> buffer and they go through atomic_dec and then they both see 0 as refcount
> value later in atomic_read. Then both will go on and execute code which
> is meant to be run just once.
The trival case should be protected by mmap_sem, we call vm_ops->close()
with mmap_sem held for writing IIRC. But yes, I think it's possible to
construct a failure here.
On Wed, Sep 16, 2020 at 03:54:02PM +0200, [email protected] wrote:
> On Wed, Sep 16, 2020 at 01:53:11PM +0200, Jiri Olsa wrote:
> > There's a possible race in perf_mmap_close when checking ring buffer's
> > mmap_count refcount value. The problem is that the mmap_count check is
> > not atomic because we call atomic_dec and atomic_read separately.
> >
> > perf_mmap_close:
> > ...
> > atomic_dec(&rb->mmap_count);
> > ...
> > if (atomic_read(&rb->mmap_count))
> > goto out_put;
> >
> > <ring buffer detach>
> > free_uid
> >
> > out_put:
> > ring_buffer_put(rb); /* could be last */
> >
> > The race can happen when we have two (or more) events sharing same ring
> > buffer and they go through atomic_dec and then they both see 0 as refcount
> > value later in atomic_read. Then both will go on and execute code which
> > is meant to be run just once.
> >
> > The code that detaches ring buffer is probably fine to be executed more
> > than once, but the problem is in calling free_uid, which will later on
> > demonstrate in related crashes and refcount warnings, like:
> >
> > refcount_t: addition on 0; use-after-free.
> > ...
> > RIP: 0010:refcount_warn_saturate+0x6d/0xf
> > ...
> > Call Trace:
> > prepare_creds+0x190/0x1e0
> > copy_creds+0x35/0x172
> > copy_process+0x471/0x1a80
> > _do_fork+0x83/0x3a0
> > __do_sys_wait4+0x83/0x90
> > __do_sys_clone+0x85/0xa0
> > do_syscall_64+0x5b/0x1e0
> > entry_SYSCALL_64_after_hwframe+0x44/0xa9
> >
> > Using atomic decrease and check instead of separated calls.
> > This fixes CVE-2020-14351.
>
> I'm tempted to remove that line; I can never seem to find anything
> useful in a CVE.
I was asked by security guys to add this, Wade?
>
> Fixes: ?
right, sry..
Fixes: 9bb5d40cd93c ("perf: Fix mmap() accounting hole");
thanks,
jirka
>
> > Acked-by: Namhyung Kim <[email protected]>
> > Tested-by: Michael Petlan <[email protected]>
> > Signed-off-by: Jiri Olsa <[email protected]>
>
The following commit has been merged into the perf/core branch of tip:
Commit-ID: f91072ed1b7283b13ca57fcfbece5a3b92726143
Gitweb: https://git.kernel.org/tip/f91072ed1b7283b13ca57fcfbece5a3b92726143
Author: Jiri Olsa <[email protected]>
AuthorDate: Wed, 16 Sep 2020 13:53:11 +02:00
Committer: Ingo Molnar <[email protected]>
CommitterDate: Mon, 12 Oct 2020 13:24:26 +02:00
perf/core: Fix race in the perf_mmap_close() function
There's a possible race in perf_mmap_close() when checking ring buffer's
mmap_count refcount value. The problem is that the mmap_count check is
not atomic because we call atomic_dec() and atomic_read() separately.
perf_mmap_close:
...
atomic_dec(&rb->mmap_count);
...
if (atomic_read(&rb->mmap_count))
goto out_put;
<ring buffer detach>
free_uid
out_put:
ring_buffer_put(rb); /* could be last */
The race can happen when we have two (or more) events sharing same ring
buffer and they go through atomic_dec() and then they both see 0 as refcount
value later in atomic_read(). Then both will go on and execute code which
is meant to be run just once.
The code that detaches ring buffer is probably fine to be executed more
than once, but the problem is in calling free_uid(), which will later on
demonstrate in related crashes and refcount warnings, like:
refcount_t: addition on 0; use-after-free.
...
RIP: 0010:refcount_warn_saturate+0x6d/0xf
...
Call Trace:
prepare_creds+0x190/0x1e0
copy_creds+0x35/0x172
copy_process+0x471/0x1a80
_do_fork+0x83/0x3a0
__do_sys_wait4+0x83/0x90
__do_sys_clone+0x85/0xa0
do_syscall_64+0x5b/0x1e0
entry_SYSCALL_64_after_hwframe+0x44/0xa9
Using atomic decrease and check instead of separated calls.
Tested-by: Michael Petlan <[email protected]>
Signed-off-by: Jiri Olsa <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>
Acked-by: Peter Zijlstra <[email protected]>
Acked-by: Namhyung Kim <[email protected]>
Acked-by: Wade Mealing <[email protected]>
Fixes: 9bb5d40cd93c ("perf: Fix mmap() accounting hole");
Link: https://lore.kernel.org/r/20200916115311.GE2301783@krava
---
kernel/events/core.c | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 45edb85..fb662eb 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -5895,11 +5895,11 @@ static void perf_pmu_output_stop(struct perf_event *event);
static void perf_mmap_close(struct vm_area_struct *vma)
{
struct perf_event *event = vma->vm_file->private_data;
-
struct perf_buffer *rb = ring_buffer_get(event);
struct user_struct *mmap_user = rb->mmap_user;
int mmap_locked = rb->mmap_locked;
unsigned long size = perf_data_size(rb);
+ bool detach_rest = false;
if (event->pmu->event_unmapped)
event->pmu->event_unmapped(event, vma->vm_mm);
@@ -5930,7 +5930,8 @@ static void perf_mmap_close(struct vm_area_struct *vma)
mutex_unlock(&event->mmap_mutex);
}
- atomic_dec(&rb->mmap_count);
+ if (atomic_dec_and_test(&rb->mmap_count))
+ detach_rest = true;
if (!atomic_dec_and_mutex_lock(&event->mmap_count, &event->mmap_mutex))
goto out_put;
@@ -5939,7 +5940,7 @@ static void perf_mmap_close(struct vm_area_struct *vma)
mutex_unlock(&event->mmap_mutex);
/* If there's still other mmap()s of this buffer, we're done. */
- if (atomic_read(&rb->mmap_count))
+ if (!detach_rest)
goto out_put;
/*