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Subject[PATCH] Staging: android: binder: Fix crashes when sharing a binder file between processes
Date
Opening the binder driver and sharing the file returned with
other processes (e.g. by calling fork) can crash the kernel.
Prevent these crashes with the following changes:
- Add a mutex to protect against two processes mmapping the
same binder_proc.
- After locking mmap_sem, check that the vma we want to access
(still) points to the same mm_struct.
- Use proc->tsk instead of current to get the files struct since
this is where we get the rlimit from.

Signed-off-by: Arve Hjønnevåg <arve@android.com>
---
drivers/staging/android/binder.c | 12 +++++++++++-
1 files changed, 11 insertions(+), 1 deletions(-)

diff --git a/drivers/staging/android/binder.c b/drivers/staging/android/binder.c
index 48cf27c..f0b7e66 100644
--- a/drivers/staging/android/binder.c
+++ b/drivers/staging/android/binder.c
@@ -38,6 +38,7 @@

static DEFINE_MUTEX(binder_lock);
static DEFINE_MUTEX(binder_deferred_lock);
+static DEFINE_MUTEX(binder_mmap_lock);

static HLIST_HEAD(binder_procs);
static HLIST_HEAD(binder_deferred_list);
@@ -632,6 +633,11 @@ static int binder_update_page_range(struct binder_proc *proc, int allocate,
if (mm) {
down_write(&mm->mmap_sem);
vma = proc->vma;
+ if (vma && mm != vma->vm_mm) {
+ pr_err("binder: %d: vma mm and task mm mismatch\n",
+ proc->pid);
+ vma = NULL;
+ }
}

if (allocate == 0)
@@ -2802,6 +2808,7 @@ static int binder_mmap(struct file *filp, struct vm_area_struct *vma)
}
vma->vm_flags = (vma->vm_flags | VM_DONTCOPY) & ~VM_MAYWRITE;

+ mutex_lock(&binder_mmap_lock);
if (proc->buffer) {
ret = -EBUSY;
failure_string = "already mapped";
@@ -2816,6 +2823,7 @@ static int binder_mmap(struct file *filp, struct vm_area_struct *vma)
}
proc->buffer = area->addr;
proc->user_buffer_offset = vma->vm_start - (uintptr_t)proc->buffer;
+ mutex_unlock(&binder_mmap_lock);

#ifdef CONFIG_CPU_CACHE_VIPT
if (cache_is_vipt_aliasing()) {
@@ -2848,7 +2856,7 @@ static int binder_mmap(struct file *filp, struct vm_area_struct *vma)
binder_insert_free_buffer(proc, buffer);
proc->free_async_space = proc->buffer_size / 2;
barrier();
- proc->files = get_files_struct(current);
+ proc->files = get_files_struct(proc->tsk);
proc->vma = vma;

/*printk(KERN_INFO "binder_mmap: %d %lx-%lx maps %p\n",
@@ -2859,10 +2867,12 @@ err_alloc_small_buf_failed:
kfree(proc->pages);
proc->pages = NULL;
err_alloc_pages_failed:
+ mutex_lock(&binder_mmap_lock);
vfree(proc->buffer);
proc->buffer = NULL;
err_get_vm_area_failed:
err_already_mapped:
+ mutex_unlock(&binder_mmap_lock);
err_bad_arg:
printk(KERN_ERR "binder_mmap: %d %lx-%lx %s failed %d\n",
proc->pid, vma->vm_start, vma->vm_end, failure_string, ret);
--
1.7.7.3
--
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