From 45d02f79b539073b76077836871de6b674e36eb4 Mon Sep 17 00:00:00 2001 From: Jann Horn Date: Wed, 16 Oct 2019 17:01:18 +0200 Subject: binder: Don't modify VMA bounds in ->mmap handler 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 Acked-by: Todd Kjos Acked-by: Christian Brauner Link: https://lore.kernel.org/r/20191016150119.154756-1-jannh@google.com Signed-off-by: Greg Kroah-Hartman --- drivers/android/binder_alloc.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) (limited to 'drivers/android/binder_alloc.c') diff --git a/drivers/android/binder_alloc.c b/drivers/android/binder_alloc.c index d42a8b2f636a..eb76a823fbb2 100644 --- a/drivers/android/binder_alloc.c +++ b/drivers/android/binder_alloc.c @@ -22,6 +22,7 @@ #include #include #include +#include #include "binder_alloc.h" #include "binder_trace.h" @@ -689,7 +690,9 @@ int binder_alloc_mmap_handler(struct binder_alloc *alloc, 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 binder_alloc *alloc, 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) { -- cgit v1.2.3