linux-kernel - [PATCH] mm: Add check for NULL for unlocked in fixup_user

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Date:   Thu, 15 Dec 2022 12:39:30 +0300
From:   Anastasia Belova <abelova@...ralinux.ru>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Anastasia Belova <abelova@...ralinux.ru>,
        Max Filippov <jcmvbkbc@...il.com>,
        Ingo Molnar <mingo@...nel.org>,
        Vineet Gupta <vgupta@...nel.org>,
        "Russell King (Oracle)" <rmk+kernel@...linux.org.uk>,
        Geert Uytterhoeven <geert@...ux-m68k.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, lvc-project@...uxtesting.org
Subject: [PATCH] mm: Add check for NULL for unlocked in fixup_user_fault

Check unlocked for NULL before dereference.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Fixes: d92725256b4f ("mm: avoid unnecessary page fault retires on shared memory types")
Signed-off-by: Anastasia Belova <abelova@...ralinux.ru>
---
 mm/gup.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/mm/gup.c b/mm/gup.c
index f212d571b563..905d5fb64c4c 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -1282,7 +1282,8 @@ int fixup_user_fault(struct mm_struct *mm,
 		 * could tell the callers so they do not need to unlock.
 		 */
 		mmap_read_lock(mm);
-		*unlocked = true;
+		if (unlocked)
+			*unlocked = true;
 		return 0;
 	}
 
-- 
2.30.2