Re: [PATCH] arch/m68k/kernel/sys_m68k: Add missing mmap_read_lock() to sys_cacheflush()

Re: [PATCH] arch/m68k/kernel/sys_m68k: Add missing mmap_read_lock() to sys_cacheflush()

[Liam Howlett]

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Forgot the fixes line.

* Liam Howlett <liam.howlett@oracle.com> [210407 16:00]:
> When the superuser flushes the entire cache, the mmap_read_lock() is not
> taken, but mmap_read_unlock() is called.  Add the missing
> mmap_read_lock() call.
> 
> Signed-off-by: Liam R. Howlett <Liam.Howlett@Oracle.com>
> ---
>  arch/m68k/kernel/sys_m68k.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/arch/m68k/kernel/sys_m68k.c b/arch/m68k/kernel/sys_m68k.c
> index 1c235d8f53f3..f55bdcb8e4f1 100644
> --- a/arch/m68k/kernel/sys_m68k.c
> +++ b/arch/m68k/kernel/sys_m68k.c
> @@ -388,6 +388,8 @@ sys_cacheflush (unsigned long addr, int scope, int cache, unsigned long len)
>  		ret = -EPERM;
>  		if (!capable(CAP_SYS_ADMIN))
>  			goto out;
> +
> +		mmap_read_lock(current->mm);
>  	} else {
>  		struct vm_area_struct *vma;
>  
> -- 
> 2.30.0

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From aeee71b15f54426f02f41a4408afbd0b5acab7ec Mon Sep 17 00:00:00 2001
From: "Liam R. Howlett" <Liam.Howlett@Oracle.com>
Date: Wed, 7 Apr 2021 11:39:06 -0400
Subject: [PATCH] arch/m68k/kernel/sys_m68k: Add missing mmap_read_lock() to
 sys_cacheflush()

When the superuser flushes the entire cache, the mmap_read_lock() is not
taken, but mmap_read_unlock() is called.  Add the missing
mmap_read_lock() call.

Fixes: cd2567b6850b (m68k: call find_vma with the mmap_sem held in
sys_cacheflush())
Signed-off-by: Liam R. Howlett <Liam.Howlett@Oracle.com>
---
 arch/m68k/kernel/sys_m68k.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/m68k/kernel/sys_m68k.c b/arch/m68k/kernel/sys_m68k.c
index 1c235d8f53f3..f55bdcb8e4f1 100644
--- a/arch/m68k/kernel/sys_m68k.c
+++ b/arch/m68k/kernel/sys_m68k.c
@@ -388,6 +388,8 @@ sys_cacheflush (unsigned long addr, int scope, int cache, unsigned long len)
 		ret = -EPERM;
 		if (!capable(CAP_SYS_ADMIN))
 			goto out;
+
+		mmap_read_lock(current->mm);
 	} else {
 		struct vm_area_struct *vma;
 
-- 
2.30.0

Re: [PATCH] arch/m68k/kernel/sys_m68k: Add missing mmap_read_lock() to sys_cacheflush()

[Matthew Wilcox]

On Thu, Apr 08, 2021 at 04:34:20PM +0000, Liam Howlett wrote:
> When the superuser flushes the entire cache, the mmap_read_lock() is not
> taken, but mmap_read_unlock() is called.  Add the missing
> mmap_read_lock() call.
> 
> Fixes: cd2567b6850b (m68k: call find_vma with the mmap_sem held in
> sys_cacheflush())
> Signed-off-by: Liam R. Howlett <Liam.Howlett@Oracle.com>

Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>

Although if it's been broken since 2014, maybe the ability of the
superuser to flush the entire cache is not needed any more and can
be removed?