Patch "Take mmap lock in cacheflush syscall" has been added to the 5.4-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    Take mmap lock in cacheflush syscall

to the 5.4-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     take-mmap-lock-in-cacheflush-syscall.patch
and it can be found in the queue-5.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 3cc567f67f91469d57e4777720b585e4b8cd0f7a
Author: Jann Horn <jannh@xxxxxxxxxx>
Date:   Fri Feb 19 14:59:35 2021 +0800

    Take mmap lock in cacheflush syscall
    
    [ Upstream commit c26958cb5a0d9053d1358258827638773f3d36ed ]
    
    We need to take the mmap lock around find_vma() and subsequent use of the
    VMA. Otherwise, we can race with concurrent operations like munmap(), which
    can lead to use-after-free accesses to freed VMAs.
    
    Fixes: 1000197d8013 ("nios2: System calls handling")
    Signed-off-by: Jann Horn <jannh@xxxxxxxxxx>
    Signed-off-by: Ley Foon Tan <ley.foon.tan@xxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/arch/nios2/kernel/sys_nios2.c b/arch/nios2/kernel/sys_nios2.c
index cd390ec4f88bf..b1ca856999521 100644
--- a/arch/nios2/kernel/sys_nios2.c
+++ b/arch/nios2/kernel/sys_nios2.c
@@ -22,6 +22,7 @@ asmlinkage int sys_cacheflush(unsigned long addr, unsigned long len,
 				unsigned int op)
 {
 	struct vm_area_struct *vma;
+	struct mm_struct *mm = current->mm;
 
 	if (len == 0)
 		return 0;
@@ -34,16 +35,22 @@ asmlinkage int sys_cacheflush(unsigned long addr, unsigned long len,
 	if (addr + len < addr)
 		return -EFAULT;
 
+	if (mmap_read_lock_killable(mm))
+		return -EINTR;
+
 	/*
 	 * Verify that the specified address region actually belongs
 	 * to this process.
 	 */
-	vma = find_vma(current->mm, addr);
-	if (vma == NULL || addr < vma->vm_start || addr + len > vma->vm_end)
+	vma = find_vma(mm, addr);
+	if (vma == NULL || addr < vma->vm_start || addr + len > vma->vm_end) {
+		mmap_read_unlock(mm);
 		return -EFAULT;
+	}
 
 	flush_cache_range(vma, addr, addr + len);
 
+	mmap_read_unlock(mm);
 	return 0;
 }