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From:   Sasha Levin <sashal@kernel.org>
To:     linux-kernel@vger.kernel.org, stable@vger.kernel.org
Cc:     Khalid Masum <khalid.masum.92@gmail.com>,
        Herbert Xu <herbert@gondor.apana.org.au>,
        syzbot+5ec9bb042ddfe9644773@syzkaller.appspotmail.com,
        Steffen Klassert <steffen.klassert@secunet.com>,
        Sasha Levin <sashal@kernel.org>, davem@davemloft.net,
        edumazet@google.com, kuba@kernel.org, pabeni@redhat.com,
        netdev@vger.kernel.org
Subject: [PATCH AUTOSEL 6.0 25/77] xfrm: Update ipcomp_scratches with NULL when freed
Date:   Sun,  9 Oct 2022 18:07:02 -0400
Message-Id: <20221009220754.1214186-25-sashal@kernel.org>
In-Reply-To: <20221009220754.1214186-1-sashal@kernel.org>
References: <20221009220754.1214186-1-sashal@kernel.org>
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From: Khalid Masum <khalid.masum.92@gmail.com>

[ Upstream commit 8a04d2fc700f717104bfb95b0f6694e448a4537f ]

Currently if ipcomp_alloc_scratches() fails to allocate memory
ipcomp_scratches holds obsolete address. So when we try to free the
percpu scratches using ipcomp_free_scratches() it tries to vfree non
existent vm area. Described below:

static void * __percpu *ipcomp_alloc_scratches(void)
{
        ...
        scratches = alloc_percpu(void *);
        if (!scratches)
                return NULL;
ipcomp_scratches does not know about this allocation failure.
Therefore holding the old obsolete address.
        ...
}

So when we free,

static void ipcomp_free_scratches(void)
{
        ...
        scratches = ipcomp_scratches;
Assigning obsolete address from ipcomp_scratches

        if (!scratches)
                return;

        for_each_possible_cpu(i)
               vfree(*per_cpu_ptr(scratches, i));
Trying to free non existent page, causing warning: trying to vfree
existent vm area.
        ...
}

Fix this breakage by updating ipcomp_scrtches with NULL when scratches
is freed

Suggested-by: Herbert Xu <herbert@gondor.apana.org.au>
Reported-by: syzbot+5ec9bb042ddfe9644773@syzkaller.appspotmail.com
Tested-by: syzbot+5ec9bb042ddfe9644773@syzkaller.appspotmail.com
Signed-off-by: Khalid Masum <khalid.masum.92@gmail.com>
Acked-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 net/xfrm/xfrm_ipcomp.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/net/xfrm/xfrm_ipcomp.c b/net/xfrm/xfrm_ipcomp.c
index cb40ff0ff28d..92ad336a83ab 100644
--- a/net/xfrm/xfrm_ipcomp.c
+++ b/net/xfrm/xfrm_ipcomp.c
@@ -203,6 +203,7 @@ static void ipcomp_free_scratches(void)
 		vfree(*per_cpu_ptr(scratches, i));
 
 	free_percpu(scratches);
+	ipcomp_scratches = NULL;
 }
 
 static void * __percpu *ipcomp_alloc_scratches(void)
-- 
2.35.1