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

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Message-Id: <20220204235849.14658-1-sdf@google.com>
Date:   Fri,  4 Feb 2022 15:58:48 -0800
From:   Stanislav Fomichev <sdf@...gle.com>
To:     netdev@...r.kernel.org, bpf@...r.kernel.org
Cc:     ast@...nel.org, daniel@...earbox.net, andrii@...nel.org,
        Stanislav Fomichev <sdf@...gle.com>,
        Lorenzo Bianconi <lorenzo@...nel.org>,
        syzbot <syzkaller@...glegroups.com>
Subject: [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.

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