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Subject[PATCH AUTOSEL 5.4 295/350] tun: fix data-race in gro_normal_list()
From: Petar Penkov <>

[ Upstream commit c39e342a050a4425348e6fe7f75827c0a1a7ebc5 ]

There is a race in the TUN driver between napi_busy_loop and
napi_gro_frags. This commit resolves the race by adding the NAPI struct
via netif_tx_napi_add, instead of netif_napi_add, which disables polling
for the NAPI struct.

KCSAN reported:
BUG: KCSAN: data-race in gro_normal_list.part.0 / napi_busy_loop

write to 0xffff8880b5d474b0 of 4 bytes by task 11205 on cpu 0:
gro_normal_list.part.0+0x77/0xb0 net/core/dev.c:5682
gro_normal_list net/core/dev.c:5678 [inline]
gro_normal_one net/core/dev.c:5692 [inline]
napi_frags_finish net/core/dev.c:5705 [inline]
napi_gro_frags+0x625/0x770 net/core/dev.c:5778
tun_get_user+0x2150/0x26a0 drivers/net/tun.c:1976
tun_chr_write_iter+0x79/0xd0 drivers/net/tun.c:2022
call_write_iter include/linux/fs.h:1895 [inline]
do_iter_readv_writev+0x487/0x5b0 fs/read_write.c:693
do_iter_write fs/read_write.c:970 [inline]
do_iter_write+0x13b/0x3c0 fs/read_write.c:951
vfs_writev+0x118/0x1c0 fs/read_write.c:1015
do_writev+0xe3/0x250 fs/read_write.c:1058
__do_sys_writev fs/read_write.c:1131 [inline]
__se_sys_writev fs/read_write.c:1128 [inline]
__x64_sys_writev+0x4e/0x60 fs/read_write.c:1128
do_syscall_64+0xcc/0x370 arch/x86/entry/common.c:290

read to 0xffff8880b5d474b0 of 4 bytes by task 11168 on cpu 1:
gro_normal_list net/core/dev.c:5678 [inline]
napi_busy_loop+0xda/0x4f0 net/core/dev.c:6126
sk_busy_loop include/net/busy_poll.h:108 [inline]
__skb_recv_udp+0x4ad/0x560 net/ipv4/udp.c:1689
udpv6_recvmsg+0x29e/0xe90 net/ipv6/udp.c:288
inet6_recvmsg+0xbb/0x240 net/ipv6/af_inet6.c:592
sock_recvmsg_nosec net/socket.c:871 [inline]
sock_recvmsg net/socket.c:889 [inline]
sock_recvmsg+0x92/0xb0 net/socket.c:885
sock_read_iter+0x15f/0x1e0 net/socket.c:967
call_read_iter include/linux/fs.h:1889 [inline]
new_sync_read+0x389/0x4f0 fs/read_write.c:414
__vfs_read+0xb1/0xc0 fs/read_write.c:427
vfs_read fs/read_write.c:461 [inline]
vfs_read+0x143/0x2c0 fs/read_write.c:446
ksys_read+0xd5/0x1b0 fs/read_write.c:587
__do_sys_read fs/read_write.c:597 [inline]
__se_sys_read fs/read_write.c:595 [inline]
__x64_sys_read+0x4c/0x60 fs/read_write.c:595
do_syscall_64+0xcc/0x370 arch/x86/entry/common.c:290

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 11168 Comm: syz-executor.0 Not tainted 5.4.0-rc6+ #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011

Fixes: 943170998b20 ("tun: enable NAPI for TUN/TAP driver")
Signed-off-by: Petar Penkov <>
Reported-by: syzbot <>
Reviewed-by: Eric Dumazet <>
Signed-off-by: David S. Miller <>
Signed-off-by: Sasha Levin <>
drivers/net/tun.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index a8d3141582a53..16564ebcde500 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -313,8 +313,8 @@ static void tun_napi_init(struct tun_struct *tun, struct tun_file *tfile,
tfile->napi_enabled = napi_en;
tfile->napi_frags_enabled = napi_en && napi_frags;
if (napi_en) {
- netif_napi_add(tun->dev, &tfile->napi, tun_napi_poll,
+ netif_tx_napi_add(tun->dev, &tfile->napi, tun_napi_poll,
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