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@xxxxxxxxx/ Fixes: 557c0c6e7df8 ("bpf: convert stackmap to pre-allocation") Signed-off-by: Tatsuhiko Yasumatsu <th.yasumatsu@xxxxxxxxx> --- - v2: Fix the overflow by changing elem_size to u64, instead of fixing it by casting one operand of the multiplication which is passed to bpf_map_area_alloc(). kernel/bpf/stackmap.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/kernel/bpf/stackmap.c b/kernel/bpf/stackmap.c index 09a3fd97d329..6e75bbee39f0 100644 --- a/kernel/bpf/stackmap.c +++ b/kernel/bpf/stackmap.c @@ -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, -- 2.25.1
