Re: [PATCH] bpf: Fix integer overflow in prealloc_elems_and_freelist()

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



On 9/25/21 7:31 AM, Tatsuhiko Yasumatsu wrote:
In prealloc_elems_and_freelist(), the multiplication to calculate the
size passed to bpf_map_area_alloc() could lead to an integer overflow.
As a result, out-of-bounds write could occur in pcpu_freelist_populate()
as reported by KASAN:

[...]
[   16.968613] BUG: KASAN: slab-out-of-bounds in pcpu_freelist_populate+0xd9/0x100
[   16.969408] Write of size 8 at addr ffff888104fc6ea0 by task crash/78
[   16.970038]
[   16.970195] CPU: 0 PID: 78 Comm: crash Not tainted 5.15.0-rc2+ #1
[   16.970878] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0-1ubuntu1.1 04/01/2014
[   16.972026] Call Trace:
[   16.972306]  dump_stack_lvl+0x34/0x44
[   16.972687]  print_address_description.constprop.0+0x21/0x140
[   16.973297]  ? pcpu_freelist_populate+0xd9/0x100
[   16.973777]  ? pcpu_freelist_populate+0xd9/0x100
[   16.974257]  kasan_report.cold+0x7f/0x11b
[   16.974681]  ? pcpu_freelist_populate+0xd9/0x100
[   16.975190]  pcpu_freelist_populate+0xd9/0x100
[   16.975669]  stack_map_alloc+0x209/0x2a0
[   16.976106]  __sys_bpf+0xd83/0x2ce0
[...]

The possibility of this overflow was originally discussed in [0], but
was overlooked.

Fix the integer overflow by casting one operand to u64.

[0] https://lore.kernel.org/bpf/728b238e-a481-eb50-98e9-b0f430ab01e7@xxxxxxxxx/

Fixes: 557c0c6e7df8 ("bpf: convert stackmap to pre-allocation")
Signed-off-by: Tatsuhiko Yasumatsu <th.yasumatsu@xxxxxxxxx>
---
  kernel/bpf/stackmap.c | 2 +-
  1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/bpf/stackmap.c b/kernel/bpf/stackmap.c
index 09a3fd97d329..8941dc83a769 100644
--- a/kernel/bpf/stackmap.c
+++ b/kernel/bpf/stackmap.c
@@ -66,7 +66,7 @@ static int prealloc_elems_and_freelist(struct bpf_stack_map *smap)
  	u32 elem_size = sizeof(struct stack_map_bucket) + smap->map.value_size;

Thanks a lot for the fix, Tatsuhiko! Could we just change the above elem_size to u64 instead?

  	int err;
- smap->elems = bpf_map_area_alloc(elem_size * smap->map.max_entries,
+	smap->elems = bpf_map_area_alloc((u64)elem_size * smap->map.max_entries,
  					 smap->map.numa_node);
  	if (!smap->elems)
  		return -ENOMEM;


Best,
Daniel



[Index of Archives]     [Linux Samsung SoC]     [Linux Rockchip SoC]     [Linux Actions SoC]     [Linux for Synopsys ARC Processors]     [Linux NFS]     [Linux NILFS]     [Linux USB Devel]     [Video for Linux]     [Linux Audio Users]     [Yosemite News]     [Linux Kernel]     [Linux SCSI]


  Powered by Linux