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bpf: Fix integer overflow in prealloc_elems_and_freelist()

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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 changing elem_size to u64 from u32.

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

Fixes: 557c0c6e7d ("bpf: convert stackmap to pre-allocation")
Signed-off-by: Tatsuhiko Yasumatsu <th.yasumatsu@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20210930135545.173698-1-th.yasumatsu@gmail.com
This commit is contained in:
Tatsuhiko Yasumatsu 2021-09-30 22:55:45 +09:00 committed by Daniel Borkmann
parent 79e3445b38
commit 30e29a9a2b
1 changed files with 2 additions and 1 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

3
kernel/bpf/stackmap.c
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@ -63,7 +63,8 @@ static inline int stack_map_data_size(struct bpf_map *map)
static int prealloc_elems_and_freelist(struct bpf_stack_map *smap)
{
u32 elem_size = sizeof(struct stack_map_bucket) + smap->map.value_size;
u64 elem_size = sizeof(struct stack_map_bucket) +
(u64)smap->map.value_size;
int err;
smap->elems = bpf_map_area_alloc(elem_size * smap->map.max_entries,