[PATCH bpf] bpf: change size to u64 for bpf_map_{area_alloc,charge_init}()

From: Björn Töpel <redacted>

The functions bpf_map_area_alloc() and bpf_map_charge_init() prior
this commit passed the size parameter as size_t. In this commit this
is changed to u64.

All users of these functions avoid size_t overflows on 32-bit systems,
by explicitly using u64 when calculating the allocation size and
memory charge cost. However, since the result was narrowed by the
size_t when passing size and cost to the functions, the overflow
handling was in vain.

Instead of changing all call sites to size_t and handle overflow at
the call site, the parameter is changed to u64 and checked in the
functions above.

Fixes: d407bd25a204 ("bpf: don't trigger OOM killer under pressure with map alloc")
Fixes: c85d69135a91 ("bpf: move memory size checks to bpf_map_charge_init()")
Signed-off-by: Björn Töpel <redacted>
---
 include/linux/bpf.h  | 4 ++--
 kernel/bpf/syscall.c | 7 +++++--
 2 files changed, 7 insertions(+), 4 deletions(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 5b9d22338606..3bf3835d0e86 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h

@@ -656,11 +656,11 @@ void bpf_map_put_with_uref(struct bpf_map *map);
 void bpf_map_put(struct bpf_map *map);
 int bpf_map_charge_memlock(struct bpf_map *map, u32 pages);
 void bpf_map_uncharge_memlock(struct bpf_map *map, u32 pages);
-int bpf_map_charge_init(struct bpf_map_memory *mem, size_t size);
+int bpf_map_charge_init(struct bpf_map_memory *mem, u64 size);
 void bpf_map_charge_finish(struct bpf_map_memory *mem);
 void bpf_map_charge_move(struct bpf_map_memory *dst,
 			 struct bpf_map_memory *src);
-void *bpf_map_area_alloc(size_t size, int numa_node);
+void *bpf_map_area_alloc(u64 size, int numa_node);
 void bpf_map_area_free(void *base);
 void bpf_map_init_from_attr(struct bpf_map *map, union bpf_attr *attr);
 

diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 0937719b87e2..ace1cfaa24b6 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c

@@ -126,7 +126,7 @@ static struct bpf_map *find_and_alloc_map(union bpf_attr *attr)
 	return map;
 }
 
-void *bpf_map_area_alloc(size_t size, int numa_node)
+void *bpf_map_area_alloc(u64 size, int numa_node)
 {
 	/* We really just want to fail instead of triggering OOM killer
 	 * under memory pressure, therefore we set __GFP_NORETRY to kmalloc,

@@ -141,6 +141,9 @@ void *bpf_map_area_alloc(size_t size, int numa_node)
 	const gfp_t flags = __GFP_NOWARN | __GFP_ZERO;
 	void *area;
 
+	if (size >= SIZE_MAX)
+		return NULL;
+
 	if (size <= (PAGE_SIZE << PAGE_ALLOC_COSTLY_ORDER)) {
 		area = kmalloc_node(size, GFP_USER | __GFP_NORETRY | flags,
 				    numa_node);

@@ -197,7 +200,7 @@ static void bpf_uncharge_memlock(struct user_struct *user, u32 pages)
 		atomic_long_sub(pages, &user->locked_vm);
 }
 
-int bpf_map_charge_init(struct bpf_map_memory *mem, size_t size)
+int bpf_map_charge_init(struct bpf_map_memory *mem, u64 size)
 {
 	u32 pages = round_up(size, PAGE_SIZE) >> PAGE_SHIFT;
 	struct user_struct *user;

-- 
2.20.1

On Tue, 29 Oct 2019 16:43:07 +0100, Björn Töpel wrote:

From: Björn Töpel <redacted>

The functions bpf_map_area_alloc() and bpf_map_charge_init() prior
this commit passed the size parameter as size_t. In this commit this
is changed to u64.

All users of these functions avoid size_t overflows on 32-bit systems,
by explicitly using u64 when calculating the allocation size and
memory charge cost. However, since the result was narrowed by the
size_t when passing size and cost to the functions, the overflow
handling was in vain.

Instead of changing all call sites to size_t and handle overflow at
the call site, the parameter is changed to u64 and checked in the
functions above.

Fixes: d407bd25a204 ("bpf: don't trigger OOM killer under pressure with map alloc")
Fixes: c85d69135a91 ("bpf: move memory size checks to bpf_map_charge_init()")
Signed-off-by: Björn Töpel <redacted>

Okay, I guess that's the smallest change we can make here.

I'd prefer we went the way of using the standard overflow handling the
kernel has, rather than proliferating this u64 + U32_MAX comparison
stuff. But it's hard to argue with the patch length in light of the
necessary backports..

Reviewed-by: Jakub Kicinski <redacted>

On Tue, 29 Oct 2019 at 17:12, Jakub Kicinski
[off-list ref] wrote:

On Tue, 29 Oct 2019 16:43:07 +0100, Björn Töpel wrote:

quoted

From: Björn Töpel <redacted>

The functions bpf_map_area_alloc() and bpf_map_charge_init() prior
this commit passed the size parameter as size_t. In this commit this
is changed to u64.

All users of these functions avoid size_t overflows on 32-bit systems,
by explicitly using u64 when calculating the allocation size and
memory charge cost. However, since the result was narrowed by the
size_t when passing size and cost to the functions, the overflow
handling was in vain.

Instead of changing all call sites to size_t and handle overflow at
the call site, the parameter is changed to u64 and checked in the
functions above.

Fixes: d407bd25a204 ("bpf: don't trigger OOM killer under pressure with map alloc")
Fixes: c85d69135a91 ("bpf: move memory size checks to bpf_map_charge_init()")
Signed-off-by: Björn Töpel <redacted>

Okay, I guess that's the smallest change we can make here.

I'd prefer we went the way of using the standard overflow handling the
kernel has, rather than proliferating this u64 + U32_MAX comparison
stuff. But it's hard to argue with the patch length in light of the
necessary backports..

I agree with you, but this is a start, and then maps can gradually
move over to standard overflow handling.

Reviewed-by: Jakub Kicinski <redacted>

On Tue, Oct 29, 2019 at 04:43:07PM +0100, Björn Töpel wrote:

From: Björn Töpel <redacted>

The functions bpf_map_area_alloc() and bpf_map_charge_init() prior
this commit passed the size parameter as size_t. In this commit this
is changed to u64.

All users of these functions avoid size_t overflows on 32-bit systems,
by explicitly using u64 when calculating the allocation size and
memory charge cost. However, since the result was narrowed by the
size_t when passing size and cost to the functions, the overflow
handling was in vain.

Instead of changing all call sites to size_t and handle overflow at
the call site, the parameter is changed to u64 and checked in the
functions above.

Fixes: d407bd25a204 ("bpf: don't trigger OOM killer under pressure with map alloc")
Fixes: c85d69135a91 ("bpf: move memory size checks to bpf_map_charge_init()")
Signed-off-by: Björn Töpel <redacted>

Applied, thanks!