netdev - Re: [PATCH bpf-next 1/2] bpf: test_run: fix overflow in xdp frags parsing

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Date:   Mon, 7 Feb 2022 14:53:30 +0100
From:   Lorenzo Bianconi <lorenzo@...nel.org>
To:     Stanislav Fomichev <sdf@...gle.com>
Cc:     netdev@...r.kernel.org, bpf@...r.kernel.org, ast@...nel.org,
        daniel@...earbox.net, andrii@...nel.org,
        syzbot <syzkaller@...glegroups.com>
Subject: Re: [PATCH bpf-next 1/2] bpf: test_run: fix overflow in xdp frags
 parsing

> When kattr->test.data_size_in > INT_MAX, signed min_t will assign
> negative value to data_len. This negative value then gets passed
> over to copy_from_user where it is converted to (big) unsigned.
> 
> Use unsigned min_t to avoid this overflow.

Thx for fixing it.

Acked-by: Lorenzo Bianconi <lorenzo@...nel.org>
> 
> usercopy: Kernel memory overwrite attempt detected to wrapped address
> (offset 0, size 18446612140539162846)!
> ------------[ cut here ]------------
> kernel BUG at mm/usercopy.c:102!
> invalid opcode: 0000 [#1] SMP KASAN
> Modules linked in:
> CPU: 0 PID: 3781 Comm: syz-executor226 Not tainted 4.15.0-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> Google 01/01/2011
> RIP: 0010:usercopy_abort+0xbd/0xbf mm/usercopy.c:102
> RSP: 0018:ffff8801e9703a38 EFLAGS: 00010286
> RAX: 000000000000006c RBX: ffffffff84fc7040 RCX: 0000000000000000
> RDX: 0000000000000000 RSI: ffffffff816560a2 RDI: ffffed003d2e0739
> RBP: ffff8801e9703a90 R08: 000000000000006c R09: 0000000000000001
> R10: 0000000000000000 R11: 0000000000000000 R12: ffffffff84fc73a0
> R13: ffffffff84fc7180 R14: ffffffff84fc7040 R15: ffffffff84fc7040
> FS:  00007f54e0bec300(0000) GS:ffff8801f6600000(0000)
> knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000000020000280 CR3: 00000001e90ea000 CR4: 00000000003426f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>  check_bogus_address mm/usercopy.c:155 [inline]
>  __check_object_size mm/usercopy.c:263 [inline]
>  __check_object_size.cold+0x8c/0xad mm/usercopy.c:253
>  check_object_size include/linux/thread_info.h:112 [inline]
>  check_copy_size include/linux/thread_info.h:143 [inline]
>  copy_from_user include/linux/uaccess.h:142 [inline]
>  bpf_prog_test_run_xdp+0xe57/0x1240 net/bpf/test_run.c:989
>  bpf_prog_test_run kernel/bpf/syscall.c:3377 [inline]
>  __sys_bpf+0xdf2/0x4a50 kernel/bpf/syscall.c:4679
>  SYSC_bpf kernel/bpf/syscall.c:4765 [inline]
>  SyS_bpf+0x26/0x50 kernel/bpf/syscall.c:4763
>  do_syscall_64+0x21a/0x3e0 arch/x86/entry/common.c:305
>  entry_SYSCALL_64_after_hwframe+0x46/0xbb
> 
> Cc: Lorenzo Bianconi <lorenzo@...nel.org>
> Fixes: 1c1949982524 ("bpf: introduce frags support to bpf_prog_test_run_xdp()")
> Reported-by: syzbot <syzkaller@...glegroups.com>
> Signed-off-by: Stanislav Fomichev <sdf@...gle.com>
> ---
>  net/bpf/test_run.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/net/bpf/test_run.c b/net/bpf/test_run.c
> index 0220b0822d77..5819a7a5e3c6 100644
> --- a/net/bpf/test_run.c
> +++ b/net/bpf/test_run.c
> @@ -960,7 +960,7 @@ int bpf_prog_test_run_xdp(struct bpf_prog *prog, const union bpf_attr *kattr,
>  		while (size < kattr->test.data_size_in) {
>  			struct page *page;
>  			skb_frag_t *frag;
> -			int data_len;
> +			u32 data_len;
>  
>  			if (sinfo->nr_frags == MAX_SKB_FRAGS) {
>  				ret = -ENOMEM;
> @@ -976,7 +976,7 @@ int bpf_prog_test_run_xdp(struct bpf_prog *prog, const union bpf_attr *kattr,
>  			frag = &sinfo->frags[sinfo->nr_frags++];
>  			__skb_frag_set_page(frag, page);
>  
> -			data_len = min_t(int, kattr->test.data_size_in - size,
> +			data_len = min_t(u32, kattr->test.data_size_in - size,
>  					 PAGE_SIZE);
>  			skb_frag_size_set(frag, data_len);
>  
> -- 
> 2.35.0.263.gb82422642f-goog
> 

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