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Message-ID: <Yw8mUVCdov6l3Cun@gondor.apana.org.au> Date: Wed, 31 Aug 2022 17:13:53 +0800 From: Herbert Xu <herbert@...dor.apana.org.au> To: Khalid Masum <khalid.masum.92@...il.com> Cc: netdev@...r.kernel.org, linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com, syzbot+5ec9bb042ddfe9644773@...kaller.appspotmail.com, Steffen Klassert <steffen.klassert@...unet.com>, "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, linux-kernel-mentees@...ts.linuxfoundation.org, Shuah Khan <skhan@...uxfoundation.org> Subject: Re: [PATCH] xfrm: Don't increase scratch users if allocation fails On Wed, Aug 31, 2022 at 07:41:26AM +0600, Khalid Masum wrote: > 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@...kaller.appspotmail.com > Signed-off-by: Khalid Masum <khalid.masum.92@...il.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; This patch is broken because on error we will always call ipcomp_free_scratches which frees any partially allocated memory and restores ipcomp_scratch_users to zero. With this patch ipcomp_scratch_users will turn negative on error. Cheers, -- Email: Herbert Xu <herbert@...dor.apana.org.au> Home Page: http://gondor.apana.org.au/~herbert/ PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
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