From: Jann Horn jannh@google.com
commit 45d02f79b539073b76077836871de6b674e36eb4 upstream.
binder_mmap() tries to prevent the creation of overly big binder mappings by silently truncating the size of the VMA to 4MiB. However, this violates the API contract of mmap(). If userspace attempts to create a large binder VMA, and later attempts to unmap that VMA, it will call munmap() on a range beyond the end of the VMA, which may have been allocated to another VMA in the meantime. This can lead to userspace memory corruption.
The following sequence of calls leads to a segfault without this commit:
int main(void) { int binder_fd = open("/dev/binder", O_RDWR); if (binder_fd == -1) err(1, "open binder"); void *binder_mapping = mmap(NULL, 0x800000UL, PROT_READ, MAP_SHARED, binder_fd, 0); if (binder_mapping == MAP_FAILED) err(1, "mmap binder"); void *data_mapping = mmap(NULL, 0x400000UL, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0); if (data_mapping == MAP_FAILED) err(1, "mmap data"); munmap(binder_mapping, 0x800000UL); *(char*)data_mapping = 1; return 0; }
Cc: stable@vger.kernel.org Signed-off-by: Jann Horn jannh@google.com Acked-by: Todd Kjos tkjos@google.com Acked-by: Christian Brauner christian.brauner@ubuntu.com Link: https://lore.kernel.org/r/20191016150119.154756-1-jannh@google.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- drivers/android/binder.c | 7 ------- drivers/android/binder_alloc.c | 6 ++++-- 2 files changed, 4 insertions(+), 9 deletions(-)
--- a/drivers/android/binder.c +++ b/drivers/android/binder.c @@ -95,10 +95,6 @@ DEFINE_SHOW_ATTRIBUTE(proc); #define SZ_1K 0x400 #endif
-#ifndef SZ_4M -#define SZ_4M 0x400000 -#endif - #define FORBIDDEN_MMAP_FLAGS (VM_WRITE)
enum { @@ -5195,9 +5191,6 @@ static int binder_mmap(struct file *filp if (proc->tsk != current->group_leader) return -EINVAL;
- if ((vma->vm_end - vma->vm_start) > SZ_4M) - vma->vm_end = vma->vm_start + SZ_4M; - binder_debug(BINDER_DEBUG_OPEN_CLOSE, "%s: %d %lx-%lx (%ld K) vma %lx pagep %lx\n", __func__, proc->pid, vma->vm_start, vma->vm_end, --- a/drivers/android/binder_alloc.c +++ b/drivers/android/binder_alloc.c @@ -22,6 +22,7 @@ #include <asm/cacheflush.h> #include <linux/uaccess.h> #include <linux/highmem.h> +#include <linux/sizes.h> #include "binder_alloc.h" #include "binder_trace.h"
@@ -689,7 +690,9 @@ int binder_alloc_mmap_handler(struct bin alloc->buffer = (void __user *)vma->vm_start; mutex_unlock(&binder_alloc_mmap_lock);
- alloc->pages = kcalloc((vma->vm_end - vma->vm_start) / PAGE_SIZE, + 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); if (alloc->pages == NULL) { @@ -697,7 +700,6 @@ int binder_alloc_mmap_handler(struct bin failure_string = "alloc page array"; goto err_alloc_pages_failed; } - alloc->buffer_size = vma->vm_end - vma->vm_start;
buffer = kzalloc(sizeof(*buffer), GFP_KERNEL); if (!buffer) {