Re: [PATCH] bpf: Fix integer overflow in argument calculation for bpf_map_area_alloc
On 1/27/21 5:23 AM, Bui Quang Minh wrote:
On Tue, Jan 26, 2021 at 09:36:57AM +, Lorenz Bauer wrote:
On Tue, 26 Jan 2021 at 08:26, Bui Quang Minh 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
Re: [PATCH] bpf: Fix integer overflow in argument calculation for bpf_map_area_alloc
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.
Re: [PATCH] bpf: Fix integer overflow in argument calculation for bpf_map_area_alloc
On Tue, Jan 26, 2021 at 09:36:57AM +, Lorenz Bauer wrote:
> On Tue, 26 Jan 2021 at 08:26, Bui Quang Minh 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.
Re: [PATCH] bpf: Fix integer overflow in argument calculation for bpf_map_area_alloc
On Tue, 26 Jan 2021 at 08:26, Bui Quang Minh 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
[PATCH] bpf: Fix integer overflow in argument calculation for bpf_map_area_alloc
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
---
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([i]);
@@ -143,7 +143,7 @@ static int dev_map_init_map(struct bpf_dtab *dtab, union
bpf_attr *attr)
spin_lock_init(>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(>map, attr);
raw_spin_lock_init(>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
