netdev - [PATCH V2 net 1/1] net/tls(TLS_SW): Fix list_del double free caused by a race condition in tls_tx

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Date:   Tue, 17 Sep 2019 21:13:56 +0000
From:   Pooja Trivedi <poojatrivedi@...il.com>
To:     netdev@...r.kernel.org
Cc:     davem@...emloft.net, jakub.kicinski@...ronome.com,
        daniel@...earbox.net, john.fastabend@...il.com, davejwatson@...com,
        aviadye@...lanox.com, borisp@...lanox.com,
        Pooja Trivedi <pooja.trivedi@...ckpath.com>
Subject: [PATCH V2 net 1/1] net/tls(TLS_SW): Fix list_del double free caused by a race condition in tls_tx_records

From: Pooja Trivedi <pooja.trivedi@...ckpath.com>

Enclosing tls_tx_records within lock_sock/release_sock pair to ensure
write-synchronization is not sufficient because socket lock gets released
under memory pressure situation by sk_wait_event while it sleeps waiting
for memory, allowing another writer into tls_tx_records. This causes a
race condition with record deletion post transmission.

To fix this bug, use a flag set in tx_bitmask field of TLS context to
ensure single writer in tls_tx_records at a time

The bug resulted in the following crash:

[  270.888952] ------------[ cut here ]------------
[  270.890450] list_del corruption, ffff91cc3753a800->prev is
LIST_POISON2 (dead000000000122)
[  270.891194] WARNING: CPU: 1 PID: 7387 at lib/list_debug.c:50
__list_del_entry_valid+0x62/0x90
[  270.892037] Modules linked in: n5pf(OE) netconsole tls(OE) bonding
intel_rapl_msr intel_rapl_common sb_edac x86_pkg_temp_thermal
intel_powerclamp coretemp kvm_intel kvm iTCO_wdt iTCO_vendor_support
irqbypass crct10dif_pclmul crc32_pclmul ghash_clmulni_intel
aesni_intel crypto_simd mei_me cryptd glue_helper ipmi_si sg mei
lpc_ich pcspkr joydev ioatdma i2c_i801 ipmi_devintf ipmi_msghandler
wmi ip_tables xfs libcrc32c sd_mod mgag200 drm_vram_helper ttm
drm_kms_helper syscopyarea sysfillrect sysimgblt fb_sys_fops drm isci
libsas ahci scsi_transport_sas libahci crc32c_intel serio_raw igb
libata ptp pps_core dca i2c_algo_bit dm_mirror dm_region_hash dm_log
dm_mod [last unloaded: nitrox_drv]
[  270.896836] CPU: 1 PID: 7387 Comm: uperf Kdump: loaded Tainted: G
        OE     5.3.0-rc4 #1
[  270.897711] Hardware name: Supermicro SYS-1027R-N3RF/X9DRW, BIOS
3.0c 03/24/2014
[  270.898597] RIP: 0010:__list_del_entry_valid+0x62/0x90
[  270.899478] Code: 00 00 00 c3 48 89 fe 48 89 c2 48 c7 c7 e0 f9 ee
8d e8 b2 cf c8 ff 0f 0b 31 c0 c3 48 89 fe 48 c7 c7 18 fa ee 8d e8 9e
cf c8 ff <0f> 0b 31 c0 c3 48 89 f2 48 89 fe 48 c7 c7 50 fa ee 8d e8 87
cf c8
[  270.901321] RSP: 0018:ffffb6ea86eb7c20 EFLAGS: 00010282
[  270.902240] RAX: 0000000000000000 RBX: ffff91cc3753c000 RCX: 0000000000000000
[  270.903157] RDX: ffff91bc3f867080 RSI: ffff91bc3f857738 RDI: ffff91bc3f857738
[  270.904074] RBP: ffff91bc36020940 R08: 0000000000000560 R09: 0000000000000000
[  270.904988] R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
[  270.905902] R13: ffff91cc3753a800 R14: ffff91cc37cc6400 R15: ffff91cc3753a800
[  270.906809] FS:  00007f454a88d700(0000) GS:ffff91bc3f840000(0000)
knlGS:0000000000000000
[  270.907715] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  270.908606] CR2: 00007f453c00292c CR3: 000000103554e003 CR4: 00000000001606e0
[  270.909490] Call Trace:
[  270.910373]  tls_tx_records+0x138/0x1c0 [tls]
[  270.911262]  tls_sw_sendpage+0x3e0/0x420 [tls]
[  270.912154]  inet_sendpage+0x52/0x90
[  270.913045]  ? direct_splice_actor+0x40/0x40
[  270.913941]  kernel_sendpage+0x1a/0x30
[  270.914831]  sock_sendpage+0x20/0x30
[  270.915714]  pipe_to_sendpage+0x62/0x90
[  270.916592]  __splice_from_pipe+0x80/0x180
[  270.917461]  ? direct_splice_actor+0x40/0x40
[  270.918334]  splice_from_pipe+0x5d/0x90
[  270.919208]  direct_splice_actor+0x35/0x40
[  270.920086]  splice_direct_to_actor+0x103/0x230
[  270.920966]  ? generic_pipe_buf_nosteal+0x10/0x10
[  270.921850]  do_splice_direct+0x9a/0xd0
[  270.922733]  do_sendfile+0x1c9/0x3d0
[  270.923612]  __x64_sys_sendfile64+0x5c/0xc0

Signed-off-by: Pooja Trivedi <pooja.trivedi@...ckpath.com>
---
 include/net/tls.h | 1 +
 net/tls/tls_sw.c  | 7 +++++++
 2 files changed, 8 insertions(+)

diff --git a/include/net/tls.h b/include/net/tls.h
index 41b2d41..f346a54 100644
--- a/include/net/tls.h
+++ b/include/net/tls.h
@@ -161,6 +161,7 @@ struct tls_sw_context_tx {
 
 #define BIT_TX_SCHEDULED	0
 #define BIT_TX_CLOSING		1
+#define BIT_TX_IN_PROGRESS	2
 	unsigned long tx_bitmask;
 };
 
diff --git a/net/tls/tls_sw.c b/net/tls/tls_sw.c
index 91d21b0..6e99c61 100644
--- a/net/tls/tls_sw.c
+++ b/net/tls/tls_sw.c
@@ -367,6 +367,10 @@ int tls_tx_records(struct sock *sk, int flags)
 	struct sk_msg *msg_en;
 	int tx_flags, rc = 0;
 
+	/* If another writer is already in tls_tx_records, backoff and leave */
+	if (test_and_set_bit(BIT_TX_IN_PROGRESS, &ctx->tx_bitmask))
+		return 0;
+
 	if (tls_is_partially_sent_record(tls_ctx)) {
 		rec = list_first_entry(&ctx->tx_list,
 				       struct tls_rec, list);
@@ -415,6 +419,9 @@ int tls_tx_records(struct sock *sk, int flags)
 	if (rc < 0 && rc != -EAGAIN)
 		tls_err_abort(sk, EBADMSG);
 
+	/* clear the bit so another writer can get into tls_tx_records */
+	clear_bit(BIT_TX_IN_PROGRESS, &ctx->tx_bitmask);
+
 	return rc;
 }
 
-- 
1.8.3.1