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From:   Khalid Masum <khalid.masum.92@gmail.com>
To:     netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
        syzkaller-bugs@googlegroups.com,
        syzbot+5ec9bb042ddfe9644773@syzkaller.appspotmail.com
Cc:     Steffen Klassert <steffen.klassert@secunet.com>,
        Herbert Xu <herbert@gondor.apana.org.au>,
        "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>,
        linux-kernel-mentees@lists.linuxfoundation.org,
        Shuah Khan <skhan@linuxfoundation.org>,
        Khalid Masum <khalid.masum.92@gmail.com>
Subject: [PATCH] xfrm: Don't increase scratch users if allocation fails
Date:   Wed, 31 Aug 2022 07:41:26 +0600
Message-Id: <20220831014126.6708-1-khalid.masum.92@gmail.com>
In-Reply-To: <00000000000092839d0581fd74ad@google.com>
References: <00000000000092839d0581fd74ad@google.com>
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ipcomp_alloc_scratches() routine increases ipcomp_scratch_users count
even if it fails to allocate memory. Therefore, ipcomp_free_scratches()
routine, when triggered, tries to vfree() non existent percpu 
ipcomp_scratches.

To fix this breakage, do not increase scratch users count if
ipcomp_alloc_scratches() fails to allocate scratches.

Reported-and-tested-by: syzbot+5ec9bb042ddfe9644773@syzkaller.appspotmail.com
Signed-off-by: Khalid Masum <khalid.masum.92@gmail.com>

---
 net/xfrm/xfrm_ipcomp.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/net/xfrm/xfrm_ipcomp.c b/net/xfrm/xfrm_ipcomp.c
index cb40ff0ff28d..af9097983139 100644
--- a/net/xfrm/xfrm_ipcomp.c
+++ b/net/xfrm/xfrm_ipcomp.c
@@ -210,13 +210,15 @@ static void * __percpu *ipcomp_alloc_scratches(void)
 	void * __percpu *scratches;
 	int i;
 
-	if (ipcomp_scratch_users++)
+	if (ipcomp_scratch_users) {
+		ipcomp_scratch_users++;
 		return ipcomp_scratches;
-
+	}
 	scratches = alloc_percpu(void *);
 	if (!scratches)
 		return NULL;
 
+	ipcomp_scratch_users++;
 	ipcomp_scratches = scratches;
 
 	for_each_possible_cpu(i) {
-- 
2.37.1