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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Jann Horn <jannh@google.com>,
        Ley Foon Tan <ley.foon.tan@intel.com>,
        Sasha Levin <sashal@kernel.org>
Subject: [PATCH 5.10 439/663] Take mmap lock in cacheflush syscall
Date:   Mon,  1 Mar 2021 17:11:27 +0100
Message-Id: <20210301161203.616326263@linuxfoundation.org>
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From: Jann Horn <jannh@google.com>

[ 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@google.com>
Signed-off-by: Ley Foon Tan <ley.foon.tan@intel.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 arch/nios2/kernel/sys_nios2.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

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;
 }
 
-- 
2.27.0