Re: ethtool_get_rxnfc: Buffer overflow detected (8 < 192)!

Salvatore Bonaccorso
2021-09-21T04:48:23Z

Hi Michal,

On Mon, Sep 20, 2021 at 11:12:25AM +0200, Michal Kubecek wrote:
> On Sat, Sep 18, 2021 at 05:52:00PM -0700, Randy Dunlap wrote:
> > [adding netdev]
> >
> > On 9/18/21 5:16 PM, Kelly Anderson wrote:
> > > New patches in 5.14.6 cause a problem in ethtool_get_rxnfc.
> > >
> > > It seems someone has allocated a variable length struct @958:ioctl.c: struct ethtool_rxnfc info.
> > > Unfortunately depending on the calls being made the struct cannot hold the variable length part of the data.
> > > Luckily the error checking caught this, otherwise it would be messing up the stack.
> > >
> > >
> > > Sep 18 15:11:27 bbb.internal kernel: Buffer overflow detected (8 < 192)!
> > > Sep 18 15:11:27 bbb.internal kernel: WARNING: CPU: 4 PID: 1434 at include/linux/thread_info.h:200 ethtool_rxnfc_copy_to_user+0x26/0xa0
> > > Sep 18 15:11:27 bbb.internal kernel: Modules linked in: xt_CHECKSUM xt_MASQUERADE ipt_REJECT nf_reject_ipv4 ip6table_mangle ip6table_nat iptable_mangle iptable_nat nf_nat ip6table_filter ip6_tables xt_tcpudp xt_set xt_LOG nf_log_syslog xt_conntrack nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 iptable_filter bpfilter ip_set_hash_ipport ip_set_list_set ip_set_hash_net ip_set_hash_ip ip_set nfnetlink amdgpu iommu_v2 gpu_sched snd_hda_codec_realtek snd_hda_codec_generic ledtrig_audio snd_hda_codec_hdmi wmi_bmof mxm_wmi sp5100_tco crct10dif_pclmul ghash_clmulni_intel pcspkr fam15h_power k10temp radeon ixgbe i2c_piix4 ptp i2c_algo_bit drm_ttm_helper snd_hda_intel pps_core ttm snd_intel_dspcfg mdio snd_intel_sdw_acpi dca drm_kms_helper snd_hda_codec xhci_pci xhci_pci_renesas snd_hda_core cec snd_pcm fb_sys_fops snd_timer syscopyarea sysfillrect snd sysimgblt soundcore wmi evdev sch_fq_codel xt_limit vhost_net vhost vhost_iotlb tap tun sha512_ssse3 sha1_ssse3 sg rpcsec_gss_krb5 r8169 realtek mdio_devres libphy macvlan
> > > Sep 18 15:11:27 bbb.internal kernel: kvm_amd ccp rng_core kvm irqbypass it87 hwmon_vid hwmon msr ftdi_sio cpuid camellia_aesni_avx_x86_64 camellia_x86_64 br_netfilter bridge stp llc aesni_intel crypto_simd cryptd drm nfsd configfs ip_tables x_tables
> > > Sep 18 15:11:27 bbb.internal kernel: CPU: 4 PID: 1434 Comm: nmbd Tainted: G T 5.14.6 #1
> > > Sep 18 15:11:27 bbb.internal kernel: Hardware name: To be filled by O.E.M. To be filled by O.E.M./SABERTOOTH 990FX R2.0, BIOS 2901 05/04/2016
> > > Sep 18 15:11:27 bbb.internal kernel: RIP: 0010:ethtool_rxnfc_copy_to_user+0x26/0xa0
> > > Sep 18 15:11:27 bbb.internal kernel: Code: ff 0f 1f 00 41 55 65 48 8b 04 25 00 6d 01 00 41 54 55 53 f6 40 10 02 75 23 be 08 00 00 00 48 c7 c7 68 16 30 aa e8 01 85 13 00 <0f> 0b 41 bc f2 ff ff ff 5b 44 89 e0 5d 41 5c 41 5d c3 48 89 fb 49
> > > Sep 18 15:11:27 bbb.internal kernel: RSP: 0018:ffffb9ca819bbb10 EFLAGS: 00010282
> > > Sep 18 15:11:27 bbb.internal kernel: RAX: 0000000000000000 RBX: ffffffffc071a440 RCX: 0000000000000027
> > > Sep 18 15:11:27 bbb.internal kernel: RDX: ffff9d78ded17508 RSI: 0000000000000001 RDI: ffff9d78ded17500
> > > Sep 18 15:11:27 bbb.internal kernel: RBP: ffffb9ca819bbb40 R08: 0000000000000000 R09: ffffb9ca819bb948
> > > Sep 18 15:11:27 bbb.internal kernel: R10: ffffb9ca819bb940 R11: ffffffffaa6beda8 R12: 0000000000000000
> > > Sep 18 15:11:27 bbb.internal kernel: R13: 00007ffe1b458980 R14: 0000000000000000 R15: ffff9d71c7e08000
> > > Sep 18 15:11:27 bbb.internal kernel: FS: 00007fcd84c55a40(0000) GS:ffff9d78ded00000(0000) knlGS:0000000000000000
> > > Sep 18 15:11:27 bbb.internal kernel: CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > > Sep 18 15:11:27 bbb.internal kernel: CR2: 00005576720f14d8 CR3: 0000000243892000 CR4: 00000000000406e0
> > > Sep 18 15:11:27 bbb.internal kernel: Call Trace:
> > > Sep 18 15:11:27 bbb.internal kernel: ethtool_get_rxnfc+0xce/0x1b0
> > > Sep 18 15:11:27 bbb.internal kernel: dev_ethtool+0xc26/0x2d90
> > > Sep 18 15:11:27 bbb.internal kernel: ? inet_ioctl+0xe5/0x210
> > > Sep 18 15:11:27 bbb.internal kernel: dev_ioctl+0x188/0x490
> > > Sep 18 15:11:27 bbb.internal kernel: sock_do_ioctl+0xe9/0x180
> > > Sep 18 15:11:27 bbb.internal kernel: sock_ioctl+0x273/0x370
> > > Sep 18 15:11:27 bbb.internal kernel: __x64_sys_ioctl+0x7c/0xb0
> > > Sep 18 15:11:27 bbb.internal kernel: do_syscall_64+0x64/0x90
> > > Sep 18 15:11:27 bbb.internal kernel: ? sock_alloc_file+0x56/0xa0
> > > Sep 18 15:11:27 bbb.internal kernel: ? get_vtime_delta+0xa/0xb0
> > > Sep 18 15:11:27 bbb.internal kernel: ? vtime_user_enter+0x17/0x70
> > > Sep 18 15:11:27 bbb.internal kernel: ? __context_tracking_enter+0x5c/0x60
> > > Sep 18 15:11:27 bbb.internal kernel: ? syscall_exit_to_user_mode+0x39/0x40
> > > Sep 18 15:11:27 bbb.internal kernel: ? do_syscall_64+0x71/0x90
> > > Sep 18 15:11:27 bbb.internal kernel: ? syscall_exit_to_user_mode+0x39/0x40
> > > Sep 18 15:11:27 bbb.internal kernel: ? do_syscall_64+0x71/0x90
> > > Sep 18 15:11:27 bbb.internal kernel: ? vtime_user_enter+0x17/0x70
> > > Sep 18 15:11:27 bbb.internal kernel: ? __context_tracking_enter+0x5c/0x60
> > > Sep 18 15:11:27 bbb.internal kernel: entry_SYSCALL_64_after_hwframe+0x44/0xae
> > > Sep 18 15:11:27 bbb.internal kernel: RIP: 0033:0x7fcd84b1a767
> > > Sep 18 15:11:27 bbb.internal kernel: Code: 3c 1c e8 2c ff ff ff 85 c0 79 97 49 c7 c4 ff ff ff ff 5b 5d 4c 89 e0 41 5c c3 66 0f 1f 84 00 00 00 00 00 b8 10 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 99 16 0f 00 f7 d8 64 89 01 48
> > > Sep 18 15:11:27 bbb.internal kernel: RSP: 002b:00007ffe1b458938 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
> > > Sep 18 15:11:27 bbb.internal kernel: RAX: ffffffffffffffda RBX: 00005576720f0160 RCX: 00007fcd84b1a767
> > > Sep 18 15:11:27 bbb.internal kernel: RDX: 00007ffe1b458950 RSI: 0000000000008946 RDI: 000000000000000f
> > > Sep 18 15:11:27 bbb.internal kernel: RBP: 00007ffe1b458a50 R08: 0000000000000000 R09: 00007fcd84b6e070
> > > Sep 18 15:11:27 bbb.internal kernel: R10: 0000000000000040 R11: 0000000000000246 R12: 00007ffe1b458ee8
> > > Sep 18 15:11:27 bbb.internal kernel: R13: 00005576702c9649 R14: 00007fcd85187c40 R15: 000055767030a350
> > > Sep 18 15:11:27 bbb.internal kernel: ---[ end trace d48f50afc5752bb2 ]---
>
> Looking at the code, I think this is the problem:
>
> static int ethtool_rxnfc_copy_to_user(void __user *useraddr,
> const struct ethtool_rxnfc *rxnfc,
> size_t size, const u32 *rule_buf)
> {
> ...
> ret = copy_to_user(useraddr, &rxnfc, size);
> ...
> }
>
> This was introduced in mainline commit dd98d2895de6 ("ethtool: improve
> compat ioctl handling"), backported into 5.14.6 stable. Unlike info
> variable in the original code, rxnfc is a pointer, not the structure, so
> that second parameter to copy_to_user() should be "rxnfc", not "&rxnfc".
>
> This was already fixed in 5.15-rc1 by commit 9b29a161ef38 ("ethtool: Fix
> rxnfc copy to user buffer overflow") which provides correct Fixes tag
> (and both in fact reached mainline in the same merge) so that it's
> rather surprising that the original commit got into stable-5.14.y
> without the follow-up fix.

FTR, it looks this followup commit has been queued as well now for the
next rounds of stable updates where this is relevant.

Regards,
Salvatore