commit 3ce00bb7e91cf57d723905371507af57182c37ef upstream.
Since commit 1da52815d5f1 ("binder: fix alloc->vma_vm_mm null-ptr
dereference") binder caches a pointer to the current->mm during open().
This fixes a null-ptr dereference reported by syzkaller. Unfortunately,
it also opens the door for a process to update its mm after the open(),
(e.g. via execve) making the cached alloc->mm pointer invalid.
Things get worse when the process continues to mmap() a vma. From this
point forward, binder will attempt to find this vma using an obsolete
alloc->mm reference. Such as in binder_update_page_range(), where the
wrong vma is obtained via vma_lookup(), yet binder proceeds to happily
insert new pages into it.
To avoid this issue fail the ->mmap() callback if we detect a mismatch
between the vma->vm_mm and the original alloc->mm pointer. This prevents
alloc->vm_addr from getting set, so that any subsequent vma_lookup()
calls fail as expected.
Fixes: 1da52815d5f1 ("binder: fix alloc->vma_vm_mm null-ptr dereference")
Reported-by: Jann Horn <[email protected]>
Cc: <[email protected]> # 5.15+
Signed-off-by: Carlos Llamas <[email protected]>
Acked-by: Todd Kjos <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>
[cmllamas: renamed alloc->mm since missing e66b77e50522]
Signed-off-by: Carlos Llamas <[email protected]>
---
drivers/android/binder_alloc.c | 7 +++++++
1 file changed, 7 insertions(+)
diff --git a/drivers/android/binder_alloc.c b/drivers/android/binder_alloc.c
index 9b1778c00610..64999777e0bf 100644
--- a/drivers/android/binder_alloc.c
+++ b/drivers/android/binder_alloc.c
@@ -760,6 +760,12 @@ int binder_alloc_mmap_handler(struct binder_alloc *alloc,
const char *failure_string;
struct binder_buffer *buffer;
+ if (unlikely(vma->vm_mm != alloc->vma_vm_mm)) {
+ ret = -EINVAL;
+ failure_string = "invalid vma->vm_mm";
+ goto err_invalid_mm;
+ }
+
mutex_lock(&binder_alloc_mmap_lock);
if (alloc->buffer_size) {
ret = -EBUSY;
@@ -806,6 +812,7 @@ int binder_alloc_mmap_handler(struct binder_alloc *alloc,
alloc->buffer_size = 0;
err_already_mapped:
mutex_unlock(&binder_alloc_mmap_lock);
+err_invalid_mm:
binder_alloc_debug(BINDER_DEBUG_USER_ERROR,
"%s: %d %lx-%lx %s failed %d\n", __func__,
alloc->pid, vma->vm_start, vma->vm_end,
--
2.38.1.584.g0f3c55d4c2-goog
On Wed, Nov 23, 2022 at 06:08:09PM +0000, Carlos Llamas wrote:
> commit 3ce00bb7e91cf57d723905371507af57182c37ef upstream.
>
> Since commit 1da52815d5f1 ("binder: fix alloc->vma_vm_mm null-ptr
> dereference") binder caches a pointer to the current->mm during open().
> This fixes a null-ptr dereference reported by syzkaller. Unfortunately,
> it also opens the door for a process to update its mm after the open(),
> (e.g. via execve) making the cached alloc->mm pointer invalid.
>
> Things get worse when the process continues to mmap() a vma. From this
> point forward, binder will attempt to find this vma using an obsolete
> alloc->mm reference. Such as in binder_update_page_range(), where the
> wrong vma is obtained via vma_lookup(), yet binder proceeds to happily
> insert new pages into it.
>
> To avoid this issue fail the ->mmap() callback if we detect a mismatch
> between the vma->vm_mm and the original alloc->mm pointer. This prevents
> alloc->vm_addr from getting set, so that any subsequent vma_lookup()
> calls fail as expected.
>
> Fixes: 1da52815d5f1 ("binder: fix alloc->vma_vm_mm null-ptr dereference")
> Reported-by: Jann Horn <[email protected]>
> Cc: <[email protected]> # 5.15+
> Signed-off-by: Carlos Llamas <[email protected]>
> Acked-by: Todd Kjos <[email protected]>
> Link: https://lore.kernel.org/r/[email protected]
> Signed-off-by: Greg Kroah-Hartman <[email protected]>
> [cmllamas: renamed alloc->mm since missing e66b77e50522]
> Signed-off-by: Carlos Llamas <[email protected]>
> ---
> drivers/android/binder_alloc.c | 7 +++++++
> 1 file changed, 7 insertions(+)
This is already in the 6.0 queue, is this a different version?
thanks,
greg k-h
On Wed, Nov 30, 2022 at 01:40:40PM +0100, Greg Kroah-Hartman wrote:
> On Wed, Nov 23, 2022 at 06:08:09PM +0000, Carlos Llamas wrote:
> > commit 3ce00bb7e91cf57d723905371507af57182c37ef upstream.
> >
> > Since commit 1da52815d5f1 ("binder: fix alloc->vma_vm_mm null-ptr
> > dereference") binder caches a pointer to the current->mm during open().
> > This fixes a null-ptr dereference reported by syzkaller. Unfortunately,
> > it also opens the door for a process to update its mm after the open(),
> > (e.g. via execve) making the cached alloc->mm pointer invalid.
> >
> > Things get worse when the process continues to mmap() a vma. From this
> > point forward, binder will attempt to find this vma using an obsolete
> > alloc->mm reference. Such as in binder_update_page_range(), where the
> > wrong vma is obtained via vma_lookup(), yet binder proceeds to happily
> > insert new pages into it.
> >
> > To avoid this issue fail the ->mmap() callback if we detect a mismatch
> > between the vma->vm_mm and the original alloc->mm pointer. This prevents
> > alloc->vm_addr from getting set, so that any subsequent vma_lookup()
> > calls fail as expected.
> >
> > Fixes: 1da52815d5f1 ("binder: fix alloc->vma_vm_mm null-ptr dereference")
> > Reported-by: Jann Horn <[email protected]>
> > Cc: <[email protected]> # 5.15+
> > Signed-off-by: Carlos Llamas <[email protected]>
> > Acked-by: Todd Kjos <[email protected]>
> > Link: https://lore.kernel.org/r/[email protected]
> > Signed-off-by: Greg Kroah-Hartman <[email protected]>
> > [cmllamas: renamed alloc->mm since missing e66b77e50522]
> > Signed-off-by: Carlos Llamas <[email protected]>
> > ---
> > drivers/android/binder_alloc.c | 7 +++++++
> > 1 file changed, 7 insertions(+)
>
> This is already in the 6.0 queue, is this a different version?
>
> thanks,
>
> greg k-h
Oh, please ignore this. It seems Sasha backported the change correctly.