* [PATCH] bpf: hashtab: fix 32-bit overflow in memory usage calculation
@ 2025-11-06 20:58 Alexei Safin
2025-11-07 1:58 ` Yafang Shao
0 siblings, 1 reply; 4+ messages in thread
From: Alexei Safin @ 2025-11-06 20:58 UTC (permalink / raw)
To: Alexei Starovoitov
Cc: Alexei Safin, Daniel Borkmann, Andrii Nakryiko, Martin KaFai Lau,
Eduard Zingerman, Song Liu, Yonghong Song, John Fastabend,
KP Singh, Stanislav Fomichev, Hao Luo, Jiri Olsa, Yafang Shao,
bpf, linux-kernel, lvc-patches, stable
The intermediate product value_size * num_possible_cpus() is evaluated
in 32-bit arithmetic and only then promoted to 64 bits. On systems with
large value_size and many possible CPUs this can overflow and lead to
an underestimated memory usage.
Cast value_size to u64 before multiplying.
Found by Linux Verification Center (linuxtesting.org) with SVACE.
Fixes: 304849a27b34 ("bpf: hashtab memory usage")
Cc: stable@vger.kernel.org
Signed-off-by: Alexei Safin <a.safin@rosa.ru>
---
kernel/bpf/hashtab.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c
index 570e2f723144..7ad6b5137ba1 100644
--- a/kernel/bpf/hashtab.c
+++ b/kernel/bpf/hashtab.c
@@ -2269,7 +2269,7 @@ static u64 htab_map_mem_usage(const struct bpf_map *map)
usage += htab->elem_size * num_entries;
if (percpu)
- usage += value_size * num_possible_cpus() * num_entries;
+ usage += (u64)value_size * num_possible_cpus() * num_entries;
else if (!lru)
usage += sizeof(struct htab_elem *) * num_possible_cpus();
} else {
@@ -2281,7 +2281,7 @@ static u64 htab_map_mem_usage(const struct bpf_map *map)
usage += (htab->elem_size + LLIST_NODE_SZ) * num_entries;
if (percpu) {
usage += (LLIST_NODE_SZ + sizeof(void *)) * num_entries;
- usage += value_size * num_possible_cpus() * num_entries;
+ usage += (u64)value_size * num_possible_cpus() * num_entries;
}
}
return usage;
--
2.50.1 (Apple Git-155)
^ permalink raw reply [flat|nested] 4+ messages in thread* Re: [PATCH] bpf: hashtab: fix 32-bit overflow in memory usage calculation
2025-11-06 20:58 [PATCH] bpf: hashtab: fix 32-bit overflow in memory usage calculation Alexei Safin
@ 2025-11-07 1:58 ` Yafang Shao
2025-11-07 6:58 ` Алексей Сафин
0 siblings, 1 reply; 4+ messages in thread
From: Yafang Shao @ 2025-11-07 1:58 UTC (permalink / raw)
To: Alexei Safin
Cc: Alexei Starovoitov, Daniel Borkmann, Andrii Nakryiko,
Martin KaFai Lau, Eduard Zingerman, Song Liu, Yonghong Song,
John Fastabend, KP Singh, Stanislav Fomichev, Hao Luo, Jiri Olsa,
bpf, linux-kernel, lvc-patches, stable
On Fri, Nov 7, 2025 at 4:59 AM Alexei Safin <a.safin@rosa.ru> wrote:
>
> The intermediate product value_size * num_possible_cpus() is evaluated
> in 32-bit arithmetic and only then promoted to 64 bits. On systems with
> large value_size and many possible CPUs this can overflow and lead to
> an underestimated memory usage.
>
> Cast value_size to u64 before multiplying.
>
> Found by Linux Verification Center (linuxtesting.org) with SVACE.
>
> Fixes: 304849a27b34 ("bpf: hashtab memory usage")
> Cc: stable@vger.kernel.org
> Signed-off-by: Alexei Safin <a.safin@rosa.ru>
> ---
> kernel/bpf/hashtab.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c
> index 570e2f723144..7ad6b5137ba1 100644
> --- a/kernel/bpf/hashtab.c
> +++ b/kernel/bpf/hashtab.c
> @@ -2269,7 +2269,7 @@ static u64 htab_map_mem_usage(const struct bpf_map *map)
> usage += htab->elem_size * num_entries;
>
> if (percpu)
> - usage += value_size * num_possible_cpus() * num_entries;
> + usage += (u64)value_size * num_possible_cpus() * num_entries;
> else if (!lru)
> usage += sizeof(struct htab_elem *) * num_possible_cpus();
> } else {
> @@ -2281,7 +2281,7 @@ static u64 htab_map_mem_usage(const struct bpf_map *map)
> usage += (htab->elem_size + LLIST_NODE_SZ) * num_entries;
> if (percpu) {
> usage += (LLIST_NODE_SZ + sizeof(void *)) * num_entries;
> - usage += value_size * num_possible_cpus() * num_entries;
> + usage += (u64)value_size * num_possible_cpus() * num_entries;
> }
> }
> return usage;
> --
> 2.50.1 (Apple Git-155)
>
Thanks for the fix. What do you think about this change?
diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c
index 4a9eeb7aef85..f9084158bfe2 100644
--- a/kernel/bpf/hashtab.c
+++ b/kernel/bpf/hashtab.c
@@ -2251,7 +2251,7 @@ static long bpf_for_each_hash_elem(struct
bpf_map *map, bpf_callback_t callback_
static u64 htab_map_mem_usage(const struct bpf_map *map)
{
struct bpf_htab *htab = container_of(map, struct bpf_htab, map);
- u32 value_size = round_up(htab->map.value_size, 8);
+ u64 value_size = round_up(htab->map.value_size, 8);
bool prealloc = htab_is_prealloc(htab);
bool percpu = htab_is_percpu(htab);
bool lru = htab_is_lru(htab);
--
Regards
Yafang
^ permalink raw reply [flat|nested] 4+ messages in thread* Re: [PATCH] bpf: hashtab: fix 32-bit overflow in memory usage calculation
2025-11-07 1:58 ` Yafang Shao
@ 2025-11-07 6:58 ` Алексей Сафин
2025-11-07 7:42 ` Yafang Shao
0 siblings, 1 reply; 4+ messages in thread
From: Алексей Сафин @ 2025-11-07 6:58 UTC (permalink / raw)
To: Yafang Shao
Cc: Alexei Starovoitov, Daniel Borkmann, Andrii Nakryiko,
Martin KaFai Lau, Eduard Zingerman, Song Liu, Yonghong Song,
John Fastabend, KP Singh, Stanislav Fomichev, Hao Luo, Jiri Olsa,
bpf, linux-kernel, lvc-patches, stable
Yes, that looks even better to me. Changing value_size to u64 at declaration
makes the arithmetic safe everywhere and keeps the code cleaner.
I agree with this version.
Should I prepare a v2 patch with this modification, or will you take it
from here?
07.11.2025 04:58, Yafang Shao пишет:
> On Fri, Nov 7, 2025 at 4:59 AM Alexei Safin <a.safin@rosa.ru> wrote:
>> The intermediate product value_size * num_possible_cpus() is evaluated
>> in 32-bit arithmetic and only then promoted to 64 bits. On systems with
>> large value_size and many possible CPUs this can overflow and lead to
>> an underestimated memory usage.
>>
>> Cast value_size to u64 before multiplying.
>>
>> Found by Linux Verification Center (linuxtesting.org) with SVACE.
>>
>> Fixes: 304849a27b34 ("bpf: hashtab memory usage")
>> Cc: stable@vger.kernel.org
>> Signed-off-by: Alexei Safin <a.safin@rosa.ru>
>> ---
>> kernel/bpf/hashtab.c | 4 ++--
>> 1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c
>> index 570e2f723144..7ad6b5137ba1 100644
>> --- a/kernel/bpf/hashtab.c
>> +++ b/kernel/bpf/hashtab.c
>> @@ -2269,7 +2269,7 @@ static u64 htab_map_mem_usage(const struct bpf_map *map)
>> usage += htab->elem_size * num_entries;
>>
>> if (percpu)
>> - usage += value_size * num_possible_cpus() * num_entries;
>> + usage += (u64)value_size * num_possible_cpus() * num_entries;
>> else if (!lru)
>> usage += sizeof(struct htab_elem *) * num_possible_cpus();
>> } else {
>> @@ -2281,7 +2281,7 @@ static u64 htab_map_mem_usage(const struct bpf_map *map)
>> usage += (htab->elem_size + LLIST_NODE_SZ) * num_entries;
>> if (percpu) {
>> usage += (LLIST_NODE_SZ + sizeof(void *)) * num_entries;
>> - usage += value_size * num_possible_cpus() * num_entries;
>> + usage += (u64)value_size * num_possible_cpus() * num_entries;
>> }
>> }
>> return usage;
>> --
>> 2.50.1 (Apple Git-155)
>>
> Thanks for the fix. What do you think about this change?
>
> diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c
> index 4a9eeb7aef85..f9084158bfe2 100644
> --- a/kernel/bpf/hashtab.c
> +++ b/kernel/bpf/hashtab.c
> @@ -2251,7 +2251,7 @@ static long bpf_for_each_hash_elem(struct
> bpf_map *map, bpf_callback_t callback_
> static u64 htab_map_mem_usage(const struct bpf_map *map)
> {
> struct bpf_htab *htab = container_of(map, struct bpf_htab, map);
> - u32 value_size = round_up(htab->map.value_size, 8);
> + u64 value_size = round_up(htab->map.value_size, 8);
> bool prealloc = htab_is_prealloc(htab);
> bool percpu = htab_is_percpu(htab);
> bool lru = htab_is_lru(htab);
>
>
^ permalink raw reply [flat|nested] 4+ messages in thread* Re: [PATCH] bpf: hashtab: fix 32-bit overflow in memory usage calculation
2025-11-07 6:58 ` Алексей Сафин
@ 2025-11-07 7:42 ` Yafang Shao
0 siblings, 0 replies; 4+ messages in thread
From: Yafang Shao @ 2025-11-07 7:42 UTC (permalink / raw)
To: Алексей
Сафин
Cc: Alexei Starovoitov, Daniel Borkmann, Andrii Nakryiko,
Martin KaFai Lau, Eduard Zingerman, Song Liu, Yonghong Song,
John Fastabend, KP Singh, Stanislav Fomichev, Hao Luo, Jiri Olsa,
bpf, linux-kernel, lvc-patches, stable
On Fri, Nov 7, 2025 at 2:58 PM Алексей Сафин <a.safin@rosa.ru> wrote:
>
> Yes, that looks even better to me. Changing value_size to u64 at declaration
> makes the arithmetic safe everywhere and keeps the code cleaner.
>
> I agree with this version.
>
> Should I prepare a v2 patch with this modification, or will you take it
> from here?
Pls send a v2
--
Regards
Yafang
^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2025-11-07 7:43 UTC | newest]
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2025-11-06 20:58 [PATCH] bpf: hashtab: fix 32-bit overflow in memory usage calculation Alexei Safin
2025-11-07 1:58 ` Yafang Shao
2025-11-07 6:58 ` Алексей Сафин
2025-11-07 7:42 ` Yafang Shao
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