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authorJann Horn2019-10-18 22:56:30 +0200
committerGreg Kroah-Hartman2019-11-14 11:44:47 +0800
commita7a74d7ff55a0c657bc46238b050460b9eacea95 (patch)
tree37be4c7f15bfa4535a2aa0a3a1a28ee58d10627f /drivers/android
parent8eb52a1ee37aafd9b796713aa0b3ab9cbc455be3 (diff)
binder: Prevent repeated use of ->mmap() via NULL mapping
binder_alloc_mmap_handler() attempts to detect the use of ->mmap() on a binder_proc whose binder_alloc has already been initialized by checking whether alloc->buffer is non-zero. Before commit 880211667b20 ("binder: remove kernel vm_area for buffer space"), alloc->buffer was a kernel mapping address, which is always non-zero, but since that commit, it is a userspace mapping address. A sufficiently privileged user can map /dev/binder at NULL, tricking binder_alloc_mmap_handler() into assuming that the binder_proc has not been mapped yet. This leads to memory unsafety. Luckily, no context on Android has such privileges, and on a typical Linux desktop system, you need to be root to do that. Fix it by using the mapping size instead of the mapping address to distinguish the mapped case. A valid VMA can't have size zero. Fixes: 880211667b20 ("binder: remove kernel vm_area for buffer space") Cc: stable@vger.kernel.org Signed-off-by: Jann Horn <jannh@google.com> Acked-by: Christian Brauner <christian.brauner@ubuntu.com> Link: https://lore.kernel.org/r/20191018205631.248274-2-jannh@google.com Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'drivers/android')
-rw-r--r--drivers/android/binder_alloc.c11
1 files changed, 6 insertions, 5 deletions
diff --git a/drivers/android/binder_alloc.c b/drivers/android/binder_alloc.c
index d718ed0537be..1f73d12409e3 100644
--- a/drivers/android/binder_alloc.c
+++ b/drivers/android/binder_alloc.c
@@ -680,17 +680,17 @@ int binder_alloc_mmap_handler(struct binder_alloc *alloc,
struct binder_buffer *buffer;
mutex_lock(&binder_alloc_mmap_lock);
- if (alloc->buffer) {
+ if (alloc->buffer_size) {
ret = -EBUSY;
failure_string = "already mapped";
goto err_already_mapped;
}
+ alloc->buffer_size = min_t(unsigned long, vma->vm_end - vma->vm_start,
+ SZ_4M);
+ mutex_unlock(&binder_alloc_mmap_lock);
alloc->buffer = (void __user *)vma->vm_start;
- mutex_unlock(&binder_alloc_mmap_lock);
- alloc->buffer_size = min_t(unsigned long, vma->vm_end - vma->vm_start,
- SZ_4M);
alloc->pages = kcalloc(alloc->buffer_size / PAGE_SIZE,
sizeof(alloc->pages[0]),
GFP_KERNEL);
@@ -721,8 +721,9 @@ err_alloc_buf_struct_failed:
kfree(alloc->pages);
alloc->pages = NULL;
err_alloc_pages_failed:
- mutex_lock(&binder_alloc_mmap_lock);
alloc->buffer = NULL;
+ mutex_lock(&binder_alloc_mmap_lock);
+ alloc->buffer_size = 0;
err_already_mapped:
mutex_unlock(&binder_alloc_mmap_lock);
binder_alloc_debug(BINDER_DEBUG_USER_ERROR,