On 2/25/20 9:39 AM, Marc Kleine-Budde wrote: > Syzbot found the use of uninitialzied memory when injecting non conformant > CANFD frames via a tun device into the kernel: > > | BUG: KMSAN: uninit-value in number+0x9f8/0x2000 lib/vsprintf.c:459 > | CPU: 1 PID: 11897 Comm: syz-executor136 Not tainted 5.6.0-rc2-syzkaller #0 > | Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 > | Call Trace: > | __dump_stack lib/dump_stack.c:77 [inline] > | dump_stack+0x1c9/0x220 lib/dump_stack.c:118 > | kmsan_report+0xf7/0x1e0 mm/kmsan/kmsan_report.c:118 > | __msan_warning+0x58/0xa0 mm/kmsan/kmsan_instr.c:215 > | number+0x9f8/0x2000 lib/vsprintf.c:459 > | vsnprintf+0x1d85/0x31b0 lib/vsprintf.c:2640 > | vscnprintf+0xc2/0x180 lib/vsprintf.c:2677 > | vprintk_store+0xef/0x11d0 kernel/printk/printk.c:1917 > | vprintk_emit+0x2c0/0x860 kernel/printk/printk.c:1984 > | vprintk_default+0x90/0xa0 kernel/printk/printk.c:2029 > | vprintk_func+0x636/0x820 kernel/printk/printk_safe.c:386 > | printk+0x18b/0x1d3 kernel/printk/printk.c:2062 > | canfd_rcv+0x370/0x3a0 net/can/af_can.c:697 > | __netif_receive_skb_one_core net/core/dev.c:5198 [inline] > | __netif_receive_skb net/core/dev.c:5312 [inline] > | netif_receive_skb_internal net/core/dev.c:5402 [inline] > | netif_receive_skb+0xe77/0xf20 net/core/dev.c:5461 > | tun_rx_batched include/linux/skbuff.h:4321 [inline] > | tun_get_user+0x6aef/0x6f60 drivers/net/tun.c:1997 > | tun_chr_write_iter+0x1f2/0x360 drivers/net/tun.c:2026 > | call_write_iter include/linux/fs.h:1901 [inline] > | new_sync_write fs/read_write.c:483 [inline] > | __vfs_write+0xa5a/0xca0 fs/read_write.c:496 > | vfs_write+0x44a/0x8f0 fs/read_write.c:558 > | ksys_write+0x267/0x450 fs/read_write.c:611 > | __do_sys_write fs/read_write.c:623 [inline] > | __se_sys_write+0x92/0xb0 fs/read_write.c:620 > | __x64_sys_write+0x4a/0x70 fs/read_write.c:620 > | do_syscall_64+0xb8/0x160 arch/x86/entry/common.c:296 > | entry_SYSCALL_64_after_hwframe+0x44/0xa9 > > In canfd_rcv() the non conformant CANFD frame (i.e. skb too short) is detected, > but the pr_warn_once() accesses uninitialized memory or the skb->data out of > bounds to print the warning message. > > This problem exists in both can_rcv() and canfd_rcv(). This patch removes the > access to the skb->data from the pr_warn_once() in both functions. > > Reported-by: syzbot+9bcb0c9409066696d3aa@xxxxxxxxxxxxxxxxxxxxxxxxx > Signed-off-by: Marc Kleine-Budde <mkl@xxxxxxxxxxxxxx> > --- > Hello, > > changes since RFC: > - print cfd->len if backed by skb, -1 otherwise > (Requested by Oliver) Doh! I have to adjust the patch description. Will do in next iteration. Marc -- Pengutronix e.K. | Marc Kleine-Budde | Embedded Linux | https://www.pengutronix.de | Vertretung West/Dortmund | Phone: +49-231-2826-924 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |
