netdev - [PATCH 2/3] xfrm: Update ipcomp_scratches with NULL when freed

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Message-ID: <20220929051357.3497325-3-steffen.klassert@secunet.com>
Date:   Thu, 29 Sep 2022 07:13:56 +0200
From:   Steffen Klassert <steffen.klassert@...unet.com>
To:     David Miller <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>
CC:     Herbert Xu <herbert@...dor.apana.org.au>,
        Steffen Klassert <steffen.klassert@...unet.com>,
        <netdev@...r.kernel.org>
Subject: [PATCH 2/3] xfrm: Update ipcomp_scratches with NULL when freed

From: Khalid Masum <khalid.masum.92@...il.com>

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@...dor.apana.org.au>
Reported-by: syzbot+5ec9bb042ddfe9644773@...kaller.appspotmail.com
Tested-by: syzbot+5ec9bb042ddfe9644773@...kaller.appspotmail.com
Signed-off-by: Khalid Masum <khalid.masum.92@...il.com>
Acked-by: Herbert Xu <herbert@...dor.apana.org.au>
Signed-off-by: Steffen Klassert <steffen.klassert@...unet.com>
---
 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)
-- 
2.25.1