Re: [PATCH 1/2] lib/scatterlist: Fix NULL pointer deference

[Ricardo Ribalda]

Hi

Friendly ping?

On Tue, Mar 9, 2021 at 9:51 PM Ricardo Ribalda <ribalda@xxxxxxxxxxxx> wrote:
>
> When sg_alloc_table_from_pages is called with n_pages = 0, we write in a
> non-allocated page. Fix it by checking early the error condition.
>
> [    7.666801] BUG: kernel NULL pointer dereference, address: 0000000000000010
> [    7.667487] #PF: supervisor read access in kernel mode
> [    7.667970] #PF: error_code(0x0000) - not-present page
> [    7.668448] PGD 0 P4D 0
> [    7.668690] Oops: 0000 [#1] SMP NOPTI
> [    7.669037] CPU: 0 PID: 184 Comm: modprobe Not tainted 5.11.0+ #2
> [    7.669606] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.14.0-2 04/01/2014
> [    7.670378] RIP: 0010:__sg_alloc_table_from_pages+0x2c5/0x4a0
> [    7.670924] Code: c9 01 48 c7 40 08 00 00 00 00 48 89 08 8b 47 0c 41 8d 44 00 ff 89 47 0c 48 81 fa 00 f0 ff ff 0f 87 d4 01 00 00 49 8b 16 89 d8 <4a> 8b 74 fd 00 4c 89 d1 44 29 f8 c1 e0 0c 44 29 d8 4c 39 d0 48 0f
> [    7.672643] RSP: 0018:ffffba1e8028fb30 EFLAGS: 00010287
> [    7.673133] RAX: 0000000000000001 RBX: 0000000000000001 RCX: 0000000000000002
> [    7.673791] RDX: 0000000000000002 RSI: ffffffffada6d0ba RDI: ffff9afe01fff820
> [    7.674448] RBP: 0000000000000010 R08: 0000000000000001 R09: 0000000000000001
> [    7.675100] R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
> [    7.675754] R13: 00000000fffff000 R14: ffff9afe01fff800 R15: 0000000000000000
> [    7.676409] FS:  00007fb0f448f540(0000) GS:ffff9afe07a00000(0000) knlGS:0000000000000000
> [    7.677151] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [    7.677681] CR2: 0000000000000010 CR3: 0000000002184001 CR4: 0000000000370ef0
> [    7.678342] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> [    7.679019] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> [    7.680349] Call Trace:
> [    7.680605]  ? device_add+0x146/0x810
> [    7.681021]  sg_alloc_table_from_pages+0x11/0x30
> [    7.681511]  vb2_dma_sg_alloc+0x162/0x280 [videobuf2_dma_sg]
>
> Cc: stable@xxxxxxxxxxxxxxx
> Fixes: efc42bc98058 ("scatterlist: add sg_alloc_table_from_pages function")
> Signed-off-by: Ricardo Ribalda <ribalda@xxxxxxxxxxxx>
> ---
>  lib/scatterlist.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/lib/scatterlist.c b/lib/scatterlist.c
> index a59778946404..1e83b6a3d930 100644
> --- a/lib/scatterlist.c
> +++ b/lib/scatterlist.c
> @@ -435,6 +435,9 @@ struct scatterlist *__sg_alloc_table_from_pages(struct sg_table *sgt,
>         unsigned int added_nents = 0;
>         struct scatterlist *s = prv;
>
> +       if (n_pages == 0)
> +               return ERR_PTR(-EINVAL);
> +
>         /*
>          * The algorithm below requires max_segment to be aligned to PAGE_SIZE
>          * otherwise it can overshoot.
> --
> 2.30.1.766.gb4fecdf3b7-goog
>


-- 
Ricardo Ribalda