linux-kernel - [PATCH] mm: fix protection of mm_struct fields in get

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Date:   Wed, 15 May 2019 11:15:37 +0300
From:   Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
To:     linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org
Cc:     Michal Hocko <mhocko@...e.com>,
        Yang Shi <yang.shi@...ux.alibaba.com>
Subject: [PATCH] mm: fix protection of mm_struct fields in get_cmdline()

Since commit 88aa7cc688d4 ("mm: introduce arg_lock to protect arg_start|
end and env_start|end in mm_struct") related mm fields are protected with
separate spinlock and mmap_sem held for read is not enough for protection.

Fixes: 88aa7cc688d4 ("mm: introduce arg_lock to protect arg_start|end and env_start|end in mm_struct")
Signed-off-by: Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
---
 mm/util.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/util.c b/mm/util.c
index e2e4f8c3fa12..540e7c157cf2 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -717,12 +717,12 @@ int get_cmdline(struct task_struct *task, char *buffer, int buflen)
 	if (!mm->arg_end)
 		goto out_mm;	/* Shh! No looking before we're done */
 
-	down_read(&mm->mmap_sem);
+	spin_lock(&mm->arg_lock);
 	arg_start = mm->arg_start;
 	arg_end = mm->arg_end;
 	env_start = mm->env_start;
 	env_end = mm->env_end;
-	up_read(&mm->mmap_sem);
+	spin_unlock(&mm->arg_lock);
 
 	len = arg_end - arg_start;