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charset=utf-8 Content-Transfer-Encoding: quoted-printable Maciej Fijalkowski writes: > Jordy says: > > " > In the xsk_map_delete_elem function an unsigned integer > (map->max_entries) is compared with a user-controlled signed integer > (k). Due to implicit type conversion, a large unsigned value for > map->max_entries can bypass the intended bounds check: > > if (k >=3D map->max_entries) > return -EINVAL; > > This allows k to hold a negative value (between -2147483648 and -2), > which is then used as an array index in m->xsk_map[k], which results > in an out-of-bounds access. > > spin_lock_bh(&m->lock); > map_entry =3D &m->xsk_map[k]; // Out-of-bounds map_entry > old_xs =3D unrcu_pointer(xchg(map_entry, NULL)); // Oob write > if (old_xs) > xsk_map_sock_delete(old_xs, map_entry); > spin_unlock_bh(&m->lock); > > The xchg operation can then be used to cause an out-of-bounds write. > Moreover, the invalid map_entry passed to xsk_map_sock_delete can lead > to further memory corruption. > " > > It indeed results in following splat: > > [76612.897343] BUG: unable to handle page fault for address: ffffc8fc2e46= 1108 > [76612.904330] #PF: supervisor write access in kernel mode > [76612.909639] #PF: error_code(0x0002) - not-present page > [76612.914855] PGD 0 P4D 0 > [76612.917431] Oops: Oops: 0002 [#1] PREEMPT SMP > [76612.921859] CPU: 11 UID: 0 PID: 10318 Comm: a.out Not tainted 6.12.0-r= c1+ #470 > [76612.929189] Hardware name: Intel Corporation S2600WFT/S2600WFT, BIOS S= E5C620.86B.02.01.0008.031920191559 03/19/2019 > [76612.939781] RIP: 0010:xsk_map_delete_elem+0x2d/0x60 > [76612.944738] Code: 00 00 41 54 55 53 48 63 2e 3b 6f 24 73 38 4c 8d a7 f= 8 00 00 00 48 89 fb 4c 89 e7 e8 2d bf 05 00 48 8d b4 eb 00 01 00 00 31 ff <= 48> 87 3e 48 85 ff 74 05 e8 16 ff ff ff 4c 89 e7 e8 3e bc 05 00 31 > [76612.963774] RSP: 0018:ffffc9002e407df8 EFLAGS: 00010246 > [76612.969079] RAX: 0000000000000000 RBX: ffffc9002e461000 RCX: 000000000= 0000000 > [76612.976323] RDX: 0000000000000001 RSI: ffffc8fc2e461108 RDI: 000000000= 0000000 > [76612.983569] RBP: ffffffff80000001 R08: 0000000000000000 R09: 000000000= 0000007 > [76612.990812] R10: ffffc9002e407e18 R11: ffff888108a38858 R12: ffffc9002= e4610f8 > [76612.998060] R13: ffff888108a38858 R14: 00007ffd1ae0ac78 R15: ffffc9002= e4610c0 > [76613.005303] FS: 00007f80b6f59740(0000) GS:ffff8897e0ec0000(0000) knlG= S:0000000000000000 > [76613.013517] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > [76613.019349] CR2: ffffc8fc2e461108 CR3: 000000011e3ef001 CR4: 000000000= 07726f0 > [76613.026595] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 000000000= 0000000 > [76613.033841] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 000000000= 0000400 > [76613.041086] PKRU: 55555554 > [76613.043842] Call Trace: > [76613.046331] > [76613.048468] ? __die+0x20/0x60 > [76613.051581] ? page_fault_oops+0x15a/0x450 > [76613.055747] ? search_extable+0x22/0x30 > [76613.059649] ? search_bpf_extables+0x5f/0x80 > [76613.063988] ? exc_page_fault+0xa9/0x140 > [76613.067975] ? asm_exc_page_fault+0x22/0x30 > [76613.072229] ? xsk_map_delete_elem+0x2d/0x60 > [76613.076573] ? xsk_map_delete_elem+0x23/0x60 > [76613.080914] __sys_bpf+0x19b7/0x23c0 > [76613.084555] __x64_sys_bpf+0x1a/0x20 > [76613.088194] do_syscall_64+0x37/0xb0 > [76613.091832] entry_SYSCALL_64_after_hwframe+0x4b/0x53 > [76613.096962] RIP: 0033:0x7f80b6d1e88d > [76613.100592] Code: 5b 41 5c c3 66 0f 1f 84 00 00 00 00 00 f3 0f 1e fa 4= 8 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <= 48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 73 b5 0f 00 f7 d8 64 89 01 48 > [76613.119631] RSP: 002b:00007ffd1ae0ac68 EFLAGS: 00000206 ORIG_RAX: 0000= 000000000141 > [76613.131330] RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f80b= 6d1e88d > [76613.142632] RDX: 0000000000000098 RSI: 00007ffd1ae0ad20 RDI: 000000000= 0000003 > [76613.153967] RBP: 00007ffd1ae0adc0 R08: 0000000000000000 R09: 000000000= 0000000 > [76613.166030] R10: 00007f80b6f77040 R11: 0000000000000206 R12: 00007ffd1= ae0aed8 > [76613.177130] R13: 000055ddf42ce1e9 R14: 000055ddf42d0d98 R15: 00007f80b= 6fab040 > [76613.188129] > > Fix this by simply changing key type from int to u32. > > Fixes: fbfc504a24f5 ("bpf: introduce new bpf AF_XDP map type BPF_MAP_TYPE= _XSKMAP") > Reported-by: Jordy Zomer > Suggested-by: Jordy Zomer > Signed-off-by: Maciej Fijalkowski Nice find! Reviewed-by: Toke H=C3=B8iland-J=C3=B8rgensen