FAILED: patch "[PATCH] binder: validate alloc->mm in ->mmap() handler" failed to apply to 5.15-stable tree

The patch below does not apply to the 5.15-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

Possible dependencies:

3ce00bb7e91c ("binder: validate alloc->mm in ->mmap() handler")

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 3ce00bb7e91cf57d723905371507af57182c37ef Mon Sep 17 00:00:00 2001
From: Carlos Llamas <[email protected]>
Date: Fri, 4 Nov 2022 23:12:35 +0000
Subject: [PATCH] binder: validate alloc->mm in ->mmap() handler

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.

index 1c39cfce32fa..4ad42b0f75cd 100644
@@ -739,6 +739,12 @@ int binder_alloc_mmap_handler(struct binder_alloc *alloc,
 	const char *failure_string;
 	struct binder_buffer *buffer;
 
+	if (unlikely(vma->vm_mm != alloc->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;

@@ -785,6 +791,7 @@ 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,