* [PATCH] bpf: Fix integer overflow in argument calculation for bpf_map_area_alloc
@ 2021-01-26 8:26 Bui Quang Minh
2021-01-26 9:36 ` Lorenz Bauer
0 siblings, 1 reply; 6+ messages in thread
From: Bui Quang Minh @ 2021-01-26 8:26 UTC (permalink / raw)
To: ast, daniel, davem, kuba, hawk, john.fastabend, andrii, kafai,
songliubraving, yhs, kpsingh, jakub, lmb
Cc: netdev, bpf, linux-kernel, minhquangbui99
In 32-bit architecture, the result of sizeof() is a 32-bit integer so
the expression becomes the multiplication between 2 32-bit integer which
can potentially leads to integer overflow. As a result,
bpf_map_area_alloc() allocates less memory than needed.
Fix this by casting 1 operand to u64.
Signed-off-by: Bui Quang Minh <minhquangbui99@gmail.com>
---
kernel/bpf/devmap.c | 4 ++--
net/core/sock_map.c | 2 +-
2 files changed, 3 insertions(+), 3 deletions(-)
diff --git a/kernel/bpf/devmap.c b/kernel/bpf/devmap.c
index f6e9c68afdd4..e849c3e8a49f 100644
--- a/kernel/bpf/devmap.c
+++ b/kernel/bpf/devmap.c
@@ -92,7 +92,7 @@ static struct hlist_head *dev_map_create_hash(unsigned int entries,
int i;
struct hlist_head *hash;
- hash = bpf_map_area_alloc(entries * sizeof(*hash), numa_node);
+ hash = bpf_map_area_alloc((u64) entries * sizeof(*hash), numa_node);
if (hash != NULL)
for (i = 0; i < entries; i++)
INIT_HLIST_HEAD(&hash[i]);
@@ -143,7 +143,7 @@ static int dev_map_init_map(struct bpf_dtab *dtab, union bpf_attr *attr)
spin_lock_init(&dtab->index_lock);
} else {
- dtab->netdev_map = bpf_map_area_alloc(dtab->map.max_entries *
+ dtab->netdev_map = bpf_map_area_alloc((u64) dtab->map.max_entries *
sizeof(struct bpf_dtab_netdev *),
dtab->map.numa_node);
if (!dtab->netdev_map)
diff --git a/net/core/sock_map.c b/net/core/sock_map.c
index 64b5ec14ff50..7a42016a981d 100644
--- a/net/core/sock_map.c
+++ b/net/core/sock_map.c
@@ -44,7 +44,7 @@ static struct bpf_map *sock_map_alloc(union bpf_attr *attr)
bpf_map_init_from_attr(&stab->map, attr);
raw_spin_lock_init(&stab->lock);
- stab->sks = bpf_map_area_alloc(stab->map.max_entries *
+ stab->sks = bpf_map_area_alloc((u64) stab->map.max_entries *
sizeof(struct sock *),
stab->map.numa_node);
if (!stab->sks) {
--
2.17.1
^ permalink raw reply related [flat|nested] 6+ messages in thread* Re: [PATCH] bpf: Fix integer overflow in argument calculation for bpf_map_area_alloc
2021-01-26 8:26 [PATCH] bpf: Fix integer overflow in argument calculation for bpf_map_area_alloc Bui Quang Minh
@ 2021-01-26 9:36 ` Lorenz Bauer
2021-01-27 4:23 ` Bui Quang Minh
0 siblings, 1 reply; 6+ messages in thread
From: Lorenz Bauer @ 2021-01-26 9:36 UTC (permalink / raw)
To: Bui Quang Minh
Cc: Alexei Starovoitov, Daniel Borkmann, David S . Miller,
Jakub Kicinski, hawk, John Fastabend, Andrii Nakryiko,
Martin Lau, Song Liu, Yonghong Song, kpsingh, Jakub Sitnicki,
Networking, bpf, LKML
On Tue, 26 Jan 2021 at 08:26, Bui Quang Minh <minhquangbui99@gmail.com> wrote:
>
> In 32-bit architecture, the result of sizeof() is a 32-bit integer so
> the expression becomes the multiplication between 2 32-bit integer which
> can potentially leads to integer overflow. As a result,
> bpf_map_area_alloc() allocates less memory than needed.
>
> Fix this by casting 1 operand to u64.
Some quick thoughts:
* Should this have a Fixes tag?
* Seems like there are quite a few similar calls scattered around
(cpumap, etc.). Did you audit these as well?
* I'd prefer a calloc style version of bpf_map_area_alloc although
that might conflict with Fixes tag.
Lorenz
--
Lorenz Bauer | Systems Engineer
6th Floor, County Hall/The Riverside Building, SE1 7PB, UK
www.cloudflare.com
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] bpf: Fix integer overflow in argument calculation for bpf_map_area_alloc
2021-01-26 9:36 ` Lorenz Bauer
@ 2021-01-27 4:23 ` Bui Quang Minh
2021-01-27 5:09 ` Bui Quang Minh
2021-01-28 0:41 ` Daniel Borkmann
0 siblings, 2 replies; 6+ messages in thread
From: Bui Quang Minh @ 2021-01-27 4:23 UTC (permalink / raw)
To: Lorenz Bauer
Cc: Alexei Starovoitov, Daniel Borkmann, David S . Miller,
Jakub Kicinski, hawk, John Fastabend, Andrii Nakryiko,
Martin Lau, Song Liu, Yonghong Song, kpsingh, Jakub Sitnicki,
Networking, bpf, LKML
On Tue, Jan 26, 2021 at 09:36:57AM +0000, Lorenz Bauer wrote:
> On Tue, 26 Jan 2021 at 08:26, Bui Quang Minh <minhquangbui99@gmail.com> wrote:
> >
> > In 32-bit architecture, the result of sizeof() is a 32-bit integer so
> > the expression becomes the multiplication between 2 32-bit integer which
> > can potentially leads to integer overflow. As a result,
> > bpf_map_area_alloc() allocates less memory than needed.
> >
> > Fix this by casting 1 operand to u64.
>
> Some quick thoughts:
> * Should this have a Fixes tag?
Ok, I will add Fixes tag in later version patch.
> * Seems like there are quite a few similar calls scattered around
> (cpumap, etc.). Did you audit these as well?
I spotted another bug after re-auditting. In hashtab, there ares 2 places using
the same calls
static struct bpf_map *htab_map_alloc(union bpf_attr *attr)
{
/* ... snip ... */
if (htab->n_buckets == 0 ||
htab->n_buckets > U32_MAX / sizeof(struct bucket))
goto free_htab;
htab->buckets = bpf_map_area_alloc(htab->n_buckets *
sizeof(struct bucket),
htab->map.numa_node);
}
This is safe because of the above check.
static int prealloc_init(struct bpf_htab *htab)
{
u32 num_entries = htab->map.max_entries;
htab->elems = bpf_map_area_alloc(htab->elem_size * num_entries,
htab->map.numa_node);
}
This is not safe since there is no limit check in elem_size.
In cpumap,
static struct bpf_map *cpu_map_alloc(union bpf_attr *attr)
{
cmap->cpu_map = bpf_map_area_alloc(cmap->map.max_entries *
sizeof(struct bpf_cpu_map_entry *),
cmap->map.numa_node);
}
I think this is safe because max_entries is not permitted to be larger than NR_CPUS.
In stackmap, there is a place that I'm not very sure about
static int prealloc_elems_and_freelist(struct bpf_stack_map *smap)
{
u32 elem_size = sizeof(struct stack_map_bucket) + smap->map.value_size;
smap->elems = bpf_map_area_alloc(elem_size * smap->map.max_entries,
smap->map.numa_node);
}
This is called after another bpf_map_area_alloc in stack_map_alloc(). In the first
bpf_map_area_alloc() the argument is calculated in an u64 variable; so if in the second
one, there is an integer overflow then the first one must be called with size > 4GB. I
think the first one will probably fail (I am not sure about the actual limit of vmalloc()),
so the second one might not be called.
Overall, I think it is error prone in this pattern, maybe we should use typecasting in all
similar calls or make a comment why we don't use typecasting. As I see typecasting is not so
expensive and we can typecast the sizeof() operand so this change only affect 32-bit
architecture.
> * I'd prefer a calloc style version of bpf_map_area_alloc although
> that might conflict with Fixes tag.
Yes, I think the calloc style will prevent this kind of integer overflow bug.
Thank you,
Quang Minh.
^ permalink raw reply [flat|nested] 6+ messages in thread* Re: [PATCH] bpf: Fix integer overflow in argument calculation for bpf_map_area_alloc
2021-01-27 4:23 ` Bui Quang Minh
@ 2021-01-27 5:09 ` Bui Quang Minh
2021-01-28 0:41 ` Daniel Borkmann
1 sibling, 0 replies; 6+ messages in thread
From: Bui Quang Minh @ 2021-01-27 5:09 UTC (permalink / raw)
To: Lorenz Bauer
Cc: Alexei Starovoitov, Daniel Borkmann, David S . Miller,
Jakub Kicinski, hawk, John Fastabend, Andrii Nakryiko,
Martin Lau, Song Liu, Yonghong Song, kpsingh, Jakub Sitnicki,
Networking, bpf, LKML
On Wed, Jan 27, 2021 at 11:23:41AM +0700, Bui Quang Minh wrote:
> > * Seems like there are quite a few similar calls scattered around
> > (cpumap, etc.). Did you audit these as well?
>
> I spotted another bug after re-auditting. In hashtab, there ares 2 places using
> the same calls
>
> static struct bpf_map *htab_map_alloc(union bpf_attr *attr)
> {
> /* ... snip ... */
> if (htab->n_buckets == 0 ||
> htab->n_buckets > U32_MAX / sizeof(struct bucket))
> goto free_htab;
>
> htab->buckets = bpf_map_area_alloc(htab->n_buckets *
> sizeof(struct bucket),
> htab->map.numa_node);
> }
>
> This is safe because of the above check.
>
> static int prealloc_init(struct bpf_htab *htab)
> {
> u32 num_entries = htab->map.max_entries;
> htab->elems = bpf_map_area_alloc(htab->elem_size * num_entries,
> htab->map.numa_node);
> }
>
> This is not safe since there is no limit check in elem_size.
So sorry but I rechecked and saw this bug in hashtab has been fixed with commit
e1868b9e36d0ca
Thank you,
Quang Minh.
^ permalink raw reply [flat|nested] 6+ messages in thread* Re: [PATCH] bpf: Fix integer overflow in argument calculation for bpf_map_area_alloc
2021-01-27 4:23 ` Bui Quang Minh
2021-01-27 5:09 ` Bui Quang Minh
@ 2021-01-28 0:41 ` Daniel Borkmann
2021-05-17 15:10 ` Bui Quang Minh
1 sibling, 1 reply; 6+ messages in thread
From: Daniel Borkmann @ 2021-01-28 0:41 UTC (permalink / raw)
To: Bui Quang Minh, Lorenz Bauer
Cc: Alexei Starovoitov, David S . Miller, Jakub Kicinski, hawk,
John Fastabend, Andrii Nakryiko, Martin Lau, Song Liu,
Yonghong Song, kpsingh, Jakub Sitnicki, Networking, bpf, LKML
On 1/27/21 5:23 AM, Bui Quang Minh wrote:
> On Tue, Jan 26, 2021 at 09:36:57AM +0000, Lorenz Bauer wrote:
>> On Tue, 26 Jan 2021 at 08:26, Bui Quang Minh <minhquangbui99@gmail.com> wrote:
>>>
>>> In 32-bit architecture, the result of sizeof() is a 32-bit integer so
>>> the expression becomes the multiplication between 2 32-bit integer which
>>> can potentially leads to integer overflow. As a result,
>>> bpf_map_area_alloc() allocates less memory than needed.
>>>
>>> Fix this by casting 1 operand to u64.
>>
>> Some quick thoughts:
>> * Should this have a Fixes tag?
>
> Ok, I will add Fixes tag in later version patch.
>
>> * Seems like there are quite a few similar calls scattered around
>> (cpumap, etc.). Did you audit these as well?
>
[...]
> In cpumap,
>
> static struct bpf_map *cpu_map_alloc(union bpf_attr *attr)
> {
> cmap->cpu_map = bpf_map_area_alloc(cmap->map.max_entries *
> sizeof(struct bpf_cpu_map_entry *),
> cmap->map.numa_node);
> }
>
> I think this is safe because max_entries is not permitted to be larger than NR_CPUS.
Yes.
> In stackmap, there is a place that I'm not very sure about
>
> static int prealloc_elems_and_freelist(struct bpf_stack_map *smap)
> {
> u32 elem_size = sizeof(struct stack_map_bucket) + smap->map.value_size;
> smap->elems = bpf_map_area_alloc(elem_size * smap->map.max_entries,
> smap->map.numa_node);
> }
>
> This is called after another bpf_map_area_alloc in stack_map_alloc(). In the first
> bpf_map_area_alloc() the argument is calculated in an u64 variable; so if in the second
> one, there is an integer overflow then the first one must be called with size > 4GB. I
> think the first one will probably fail (I am not sure about the actual limit of vmalloc()),
> so the second one might not be called.
I would sanity check this as well. Looks like k*alloc()/v*alloc() call sites typically
use array_size() which returns SIZE_MAX on overflow, 610b15c50e86 ("overflow.h: Add
allocation size calculation helpers").
Thanks,
Daniel
^ permalink raw reply [flat|nested] 6+ messages in thread* Re: [PATCH] bpf: Fix integer overflow in argument calculation for bpf_map_area_alloc
2021-01-28 0:41 ` Daniel Borkmann
@ 2021-05-17 15:10 ` Bui Quang Minh
0 siblings, 0 replies; 6+ messages in thread
From: Bui Quang Minh @ 2021-05-17 15:10 UTC (permalink / raw)
To: Daniel Borkmann, Lorenz Bauer
Cc: Alexei Starovoitov, David S . Miller, Jakub Kicinski, hawk,
John Fastabend, Andrii Nakryiko, Martin Lau, Song Liu,
Yonghong Song, kpsingh, Jakub Sitnicki, Networking, bpf, LKML
On 1/28/21 7:41 AM, Daniel Borkmann wrote:
> On 1/27/21 5:23 AM, Bui Quang Minh wrote:
>> On Tue, Jan 26, 2021 at 09:36:57AM +0000, Lorenz Bauer wrote:
>>> On Tue, 26 Jan 2021 at 08:26, Bui Quang Minh
>>> <minhquangbui99@gmail.com> wrote:
>>>>
>>>> In 32-bit architecture, the result of sizeof() is a 32-bit integer so
>>>> the expression becomes the multiplication between 2 32-bit integer
>>>> which
>>>> can potentially leads to integer overflow. As a result,
>>>> bpf_map_area_alloc() allocates less memory than needed.
>>>>
>>>> Fix this by casting 1 operand to u64.
>>>
>>> Some quick thoughts:
>>> * Should this have a Fixes tag?
>>
>> Ok, I will add Fixes tag in later version patch.
>>
>>> * Seems like there are quite a few similar calls scattered around
>>> (cpumap, etc.). Did you audit these as well?
>>
> [...]
>> In cpumap,
>>
>> static struct bpf_map *cpu_map_alloc(union bpf_attr *attr)
>> {
>> cmap->cpu_map = bpf_map_area_alloc(cmap->map.max_entries *
>> sizeof(struct bpf_cpu_map_entry *),
>> cmap->map.numa_node);
>> }
>>
>> I think this is safe because max_entries is not permitted to be larger
>> than NR_CPUS.
>
> Yes.
>
>> In stackmap, there is a place that I'm not very sure about
>>
>> static int prealloc_elems_and_freelist(struct bpf_stack_map *smap)
>> {
>> u32 elem_size = sizeof(struct stack_map_bucket) +
>> smap->map.value_size;
>> smap->elems = bpf_map_area_alloc(elem_size *
>> smap->map.max_entries,
>> smap->map.numa_node);
>> }
>>
>> This is called after another bpf_map_area_alloc in stack_map_alloc().
>> In the first
>> bpf_map_area_alloc() the argument is calculated in an u64 variable; so
>> if in the second
>> one, there is an integer overflow then the first one must be called
>> with size > 4GB. I
>> think the first one will probably fail (I am not sure about the actual
>> limit of vmalloc()),
>> so the second one might not be called.
>
> I would sanity check this as well. Looks like k*alloc()/v*alloc() call
> sites typically
> use array_size() which returns SIZE_MAX on overflow, 610b15c50e86
> ("overflow.h: Add
> allocation size calculation helpers").
Hi,
I almost forget about this patch, I have checked the bpf_map_area_alloc
in in stackmap.c and I can see that integer overflow cannot happen in
this stackmap.c case.
In stack_map_alloc(),
u64 cost;
...
cost = n_buckets * sizeof(struct stack_map_bucket *) + sizeof(*smap);
cost += n_buckets * (value_size + sizeof(struct stack_map_bucket));
smap = bpf_map_area_alloc(cost, bpf_map_attr_numa_node(attr)); (1)
...
prealloc_elems_and_freelist(smap);
In prealloc_elems_and_freelist(),
u32 elem_size = sizeof(struct stack_map_bucket) + smap->map.value_size;
smap->elems = bpf_map_area_alloc(elem_size * smap->map.max_entries,
smap->map.numa_node); (2)
Argument calculation at (1) is safe. Argument calculation at (2) can
potentially result in an integer overflow in 32-bit architecture.
However, if the integer overflow happens, it means argument at (1) must
be 2**32, which cannot pass the SIZE_MAX check in __bpf_map_area_alloc()
In __bpf_map_area_alloc()
if (size >= SIZE_MAX)
return NULL;
So I think the original patch has fixed instances of this bug pattern.
Thank you,
Quang Minh.
^ permalink raw reply [flat|nested] 6+ messages in thread
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2021-01-26 8:26 [PATCH] bpf: Fix integer overflow in argument calculation for bpf_map_area_alloc Bui Quang Minh
2021-01-26 9:36 ` Lorenz Bauer
2021-01-27 4:23 ` Bui Quang Minh
2021-01-27 5:09 ` Bui Quang Minh
2021-01-28 0:41 ` Daniel Borkmann
2021-05-17 15:10 ` Bui Quang Minh
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