On Fri, Oct 25, 2024 at 9:20 AM Hou Tao <houtao@xxxxxxxxxxxxxxx> wrote:
>
> From: Hou Tao <houtao1@xxxxxxxxxx>
>
> bpf_iter_bits_destroy() uses "kit->nr_bits <= 64" to check whether the
> bits are dynamically allocated. However, the check is incorrect and may
> cause a kmemleak as shown below:
>
> unreferenced object 0xffff88812628c8c0 (size 32):
> comm "swapper/0", pid 1, jiffies 4294727320
> hex dump (first 32 bytes):
> b0 c1 55 f5 81 88 ff ff f0 f0 f0 f0 f0 f0 f0 f0 ..U...........
> f0 f0 f0 f0 f0 f0 f0 f0 00 00 00 00 00 00 00 00 ..............
> backtrace (crc 781e32cc):
> [<00000000c452b4ab>] kmemleak_alloc+0x4b/0x80
> [<0000000004e09f80>] __kmalloc_node_noprof+0x480/0x5c0
> [<00000000597124d6>] __alloc.isra.0+0x89/0xb0
> [<000000004ebfffcd>] alloc_bulk+0x2af/0x720
> [<00000000d9c10145>] prefill_mem_cache+0x7f/0xb0
> [<00000000ff9738ff>] bpf_mem_alloc_init+0x3e2/0x610
> [<000000008b616eac>] bpf_global_ma_init+0x19/0x30
> [<00000000fc473efc>] do_one_initcall+0xd3/0x3c0
> [<00000000ec81498c>] kernel_init_freeable+0x66a/0x940
> [<00000000b119f72f>] kernel_init+0x20/0x160
> [<00000000f11ac9a7>] ret_from_fork+0x3c/0x70
> [<0000000004671da4>] ret_from_fork_asm+0x1a/0x30
>
> That is because nr_bits will be set as zero in bpf_iter_bits_next()
> after all bits have been iterated.
>
> Fix the issue by setting kit->bit to kit->nr_bits instead of setting
> kit->nr_bits to zero when the iteration completes in
> bpf_iter_bits_next(). In addition, use "!nr_bits || bits >= nr_bits" to
> check whether the iteration is complete and still use "nr_bits > 64" to
> indicate whether bits are dynamically allocated. The "!nr_bits" check is
> necessary because bpf_iter_bits_new() may fail before setting
> kit->nr_bits, and this condition will stop the iteration early instead
> of accessing the zeroed or freed kit->bits.
>
> Considering the initial value of kit->bits is -1 and the type of
> kit->nr_bits is unsigned int, change the type of kit->nr_bits to int.
> The potential overflow problem will be handled in the following patch.
>
> Fixes: 4665415975b0 ("bpf: Add bits iterator")
> Signed-off-by: Hou Tao <houtao1@xxxxxxxxxx>
LGTM
Acked-by: Yafang Shao <laoar.shao@xxxxxxxxx>
> ---
> kernel/bpf/helpers.c | 11 +++++------
> 1 file changed, 5 insertions(+), 6 deletions(-)
>
> diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
> index 1a43d06eab28..40ef6a56619f 100644
> --- a/kernel/bpf/helpers.c
> +++ b/kernel/bpf/helpers.c
> @@ -2856,7 +2856,7 @@ struct bpf_iter_bits_kern {
> unsigned long *bits;
> unsigned long bits_copy;
> };
> - u32 nr_bits;
> + int nr_bits;
> int bit;
> } __aligned(8);
>
> @@ -2930,17 +2930,16 @@ bpf_iter_bits_new(struct bpf_iter_bits *it, const u64 *unsafe_ptr__ign, u32 nr_w
> __bpf_kfunc int *bpf_iter_bits_next(struct bpf_iter_bits *it)
> {
> struct bpf_iter_bits_kern *kit = (void *)it;
> - u32 nr_bits = kit->nr_bits;
> + int bit = kit->bit, nr_bits = kit->nr_bits;
> const unsigned long *bits;
> - int bit;
>
> - if (nr_bits == 0)
> + if (!nr_bits || bit >= nr_bits)
> return NULL;
>
> bits = nr_bits == 64 ? &kit->bits_copy : kit->bits;
> - bit = find_next_bit(bits, nr_bits, kit->bit + 1);
> + bit = find_next_bit(bits, nr_bits, bit + 1);
> if (bit >= nr_bits) {
> - kit->nr_bits = 0;
> + kit->bit = bit;
> return NULL;
> }
>
> --
> 2.29.2
>
--
Regards
Yafang
