[PATCH v2] xfrm: ipcomp: Update ipcomp_scratches with NULL if alloc fails

Khalid Masum
2022-08-31T14:30:17Z

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;
Receiving obsolete addresses 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.

...
}

Fix this breakage by updating ipcomp_scratches with NULL if
the above mentioned allocation fails.

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

---
diff --git a/net/xfrm/xfrm_ipcomp.c b/net/xfrm/xfrm_ipcomp.c
index cb40ff0ff28d..17815cde8a7f 100644
--- a/net/xfrm/xfrm_ipcomp.c
+++ b/net/xfrm/xfrm_ipcomp.c
@@ -215,7 +215,7 @@ static void * __percpu *ipcomp_alloc_scratches(void)

scratches = alloc_percpu(void *);
if (!scratches)
- return NULL;
+ return ipcomp_scratches = NULL;

ipcomp_scratches = scratches;