@@ -570,6 +570,12 @@ static int binder_update_page_range(struct binder_proc *proc, int allocate,
if (mm) {
down_write(&mm->mmap_sem);
+ if (!mmget_still_valid(mm)) {
+ if (allocate == 0)
+ goto free_range;
+ goto err_no_vma;
+ }
+
vma = proc->vma;
if (vma && mm != proc->vma_vm_mm) {
pr_err("%d: vma mm and task mm mismatch\n",
@@ -947,6 +947,24 @@ static ssize_t clear_refs_write(struct file *file, const char __user *buf,
continue;
up_read(&mm->mmap_sem);
down_write(&mm->mmap_sem);
+ /*
+ * Avoid to modify vma->vm_flags
+ * without locked ops while the
+ * coredump reads the vm_flags.
+ */
+ if (!mmget_still_valid(mm)) {
+ /*
+ * Silently return "count"
+ * like if get_task_mm()
+ * failed. FIXME: should this
+ * function have returned
+ * -ESRCH if get_task_mm()
+ * failed like if
+ * get_proc_task() fails?
+ */
+ up_write(&mm->mmap_sem);
+ goto out_mm;
+ }
for (vma = mm->mmap; vma; vma = vma->vm_next) {
vma->vm_flags &= ~VM_SOFTDIRTY;
vma_set_page_prot(vma);
@@ -443,6 +443,8 @@ static int userfaultfd_release(struct inode *inode, struct file *file)
* taking the mmap_sem for writing.
*/
down_write(&mm->mmap_sem);
+ if (!mmget_still_valid(mm))
+ goto skip_mm;
prev = NULL;
for (vma = mm->mmap; vma; vma = vma->vm_next) {
cond_resched();
@@ -465,6 +467,7 @@ static int userfaultfd_release(struct inode *inode, struct file *file)
vma->vm_flags = new_flags;
vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
}
+skip_mm:
up_write(&mm->mmap_sem);
/*
@@ -761,9 +764,10 @@ static int userfaultfd_register(struct userfaultfd_ctx *ctx,
end = start + uffdio_register.range.len;
down_write(&mm->mmap_sem);
- vma = find_vma_prev(mm, start, &prev);
-
ret = -ENOMEM;
+ if (!mmget_still_valid(mm))
+ goto out_unlock;
+ vma = find_vma_prev(mm, start, &prev);
if (!vma)
goto out_unlock;
@@ -903,6 +907,8 @@ static int userfaultfd_unregister(struct userfaultfd_ctx *ctx,
end = start + uffdio_unregister.len;
down_write(&mm->mmap_sem);
+ if (!mmget_still_valid(mm))
+ goto out_unlock;
vma = find_vma_prev(mm, start, &prev);
ret = -ENOMEM;
@@ -1098,6 +1098,27 @@ void zap_page_range(struct vm_area_struct *vma, unsigned long address,
void unmap_vmas(struct mmu_gather *tlb, struct vm_area_struct *start_vma,
unsigned long start, unsigned long end);
+/*
+ * This has to be called after a get_task_mm()/mmget_not_zero()
+ * followed by taking the mmap_sem for writing before modifying the
+ * vmas or anything the coredump pretends not to change from under it.
+ *
+ * NOTE: find_extend_vma() called from GUP context is the only place
+ * that can modify the "mm" (notably the vm_start/end) under mmap_sem
+ * for reading and outside the context of the process, so it is also
+ * the only case that holds the mmap_sem for reading that must call
+ * this function. Generally if the mmap_sem is hold for reading
+ * there's no need of this check after get_task_mm()/mmget_not_zero().
+ *
+ * This function can be obsoleted and the check can be removed, after
+ * the coredump code will hold the mmap_sem for writing before
+ * invoking the ->core_dump methods.
+ */
+static inline bool mmget_still_valid(struct mm_struct *mm)
+{
+ return likely(!mm->core_state);
+}
+
/**
* mm_walk - callbacks for walk_page_range
* @pmd_entry: if set, called for each non-empty PMD (3rd-level) entry
@@ -42,6 +42,7 @@
#include <linux/memory.h>
#include <linux/printk.h>
#include <linux/userfaultfd_k.h>
+#include <linux/mm.h>
#include <asm/uaccess.h>
#include <asm/cacheflush.h>
@@ -2398,7 +2399,8 @@ find_extend_vma(struct mm_struct *mm, unsigned long addr)
vma = find_vma_prev(mm, addr, &prev);
if (vma && (vma->vm_start <= addr))
return vma;
- if (!prev || expand_stack(prev, addr))
+ /* don't alter vm_end if the coredump is running */
+ if (!prev || !mmget_still_valid(mm) || expand_stack(prev, addr))
return NULL;
if (prev->vm_flags & VM_LOCKED)
populate_vma_page_range(prev, addr, prev->vm_end, NULL);
@@ -2424,6 +2426,9 @@ find_extend_vma(struct mm_struct *mm, unsigned long addr)
return vma;
if (!(vma->vm_flags & VM_GROWSDOWN))
return NULL;
+ /* don't alter vm_start if the coredump is running */
+ if (!mmget_still_valid(mm))
+ return NULL;
start = vma->vm_start;
if (expand_stack(vma, addr))
return NULL;