KASAN: slab-out-of-bounds Read in fb_pad_aligned_buffer

Tue Jan 21 08:07:08 UTC 2020

Hello,

syzbot found the following crash on:

HEAD commit:    2747d5fd Add linux-next specific files for 20200116
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=14c99b59e00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=22f506e7a3a37fe2
dashboard link: https://syzkaller.appspot.com/bug?extid=be70641646cda31e78d9
compiler:       gcc (GCC) 9.0.0 20181231 (experimental)

Unfortunately, I don't have any reproducer for this crash yet.

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+be70641646cda31e78d9 at syzkaller.appspotmail.com

==================================================================
BUG: KASAN: slab-out-of-bounds in __fb_pad_aligned_buffer include/linux/fb.h:655 [inline]
BUG: KASAN: slab-out-of-bounds in fb_pad_aligned_buffer+0x138/0x160 drivers/video/fbdev/core/fbmem.c:116
Read of size 1 at addr ffff88804eb51fd0 by task syz-executor.4/12300

CPU: 0 PID: 12300 Comm: syz-executor.4 Not tainted 5.5.0-rc6-next-20200116-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+0x197/0x210 lib/dump_stack.c:118
 print_address_description.constprop.0.cold+0xd4/0x30b mm/kasan/report.c:374
 __kasan_report.cold+0x1b/0x32 mm/kasan/report.c:506
 kasan_report+0x12/0x20 mm/kasan/common.c:641
 __asan_report_load1_noabort+0x14/0x20 mm/kasan/generic_report.c:132
 __fb_pad_aligned_buffer include/linux/fb.h:655 [inline]
 fb_pad_aligned_buffer+0x138/0x160 drivers/video/fbdev/core/fbmem.c:116
 bit_putcs_aligned drivers/video/fbdev/core/bitblit.c:99 [inline]
 bit_putcs+0xd14/0xf10 drivers/video/fbdev/core/bitblit.c:185
 fbcon_putcs+0x33c/0x3e0 drivers/video/fbdev/core/fbcon.c:1359
 con_flush drivers/tty/vt/vt.c:2546 [inline]
 do_con_write.part.0+0xebd/0x1ef0 drivers/tty/vt/vt.c:2799
 do_con_write drivers/tty/vt/vt.c:2565 [inline]
 con_write+0x46/0xd0 drivers/tty/vt/vt.c:3135
 process_output_block drivers/tty/n_tty.c:595 [inline]
 n_tty_write+0x40e/0x1080 drivers/tty/n_tty.c:2333
 do_tty_write drivers/tty/tty_io.c:962 [inline]
 tty_write+0x496/0x7f0 drivers/tty/tty_io.c:1046
 __vfs_write+0x8a/0x110 fs/read_write.c:494
 vfs_write+0x268/0x5d0 fs/read_write.c:558
 ksys_write+0x14f/0x290 fs/read_write.c:611
 __do_sys_write fs/read_write.c:623 [inline]
 __se_sys_write fs/read_write.c:620 [inline]
 __x64_sys_write+0x73/0xb0 fs/read_write.c:620
 do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x45b349
Code: ad b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 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 0f 83 7b b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f7d0c75ac78 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007f7d0c75b6d4 RCX: 000000000045b349
RDX: 00000000000000fc RSI: 0000000020000180 RDI: 0000000000000007
RBP: 000000000075bfc8 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
R13: 0000000000000be9 R14: 00000000004c8999 R15: 000000000075bfd4

Allocated by task 10134:
 save_stack+0x23/0x90 mm/kasan/common.c:72
 set_track mm/kasan/common.c:80 [inline]
 __kasan_kmalloc mm/kasan/common.c:515 [inline]
 __kasan_kmalloc.constprop.0+0xcf/0xe0 mm/kasan/common.c:488
 kasan_kmalloc+0x9/0x10 mm/kasan/common.c:529
 __do_kmalloc mm/slab.c:3656 [inline]
 __kmalloc+0x163/0x770 mm/slab.c:3665
 kmalloc include/linux/slab.h:560 [inline]
 fbcon_set_font+0x32d/0x860 drivers/video/fbdev/core/fbcon.c:2669
 con_font_set drivers/tty/vt/vt.c:4538 [inline]
 con_font_op+0xe30/0x1270 drivers/tty/vt/vt.c:4603
 vt_ioctl+0x181a/0x26d0 drivers/tty/vt/vt_ioctl.c:965
 tty_ioctl+0xa37/0x14f0 drivers/tty/tty_io.c:2660
 vfs_ioctl fs/ioctl.c:47 [inline]
 ksys_ioctl+0x123/0x180 fs/ioctl.c:760
 __do_sys_ioctl fs/ioctl.c:769 [inline]
 __se_sys_ioctl fs/ioctl.c:767 [inline]
 __x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:767
 do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 9748:
 save_stack+0x23/0x90 mm/kasan/common.c:72
 set_track mm/kasan/common.c:80 [inline]
 kasan_set_free_info mm/kasan/common.c:337 [inline]
 __kasan_slab_free+0x102/0x150 mm/kasan/common.c:476
 kasan_slab_free+0xe/0x10 mm/kasan/common.c:485
 __cache_free mm/slab.c:3426 [inline]
 kfree+0x10a/0x2c0 mm/slab.c:3757
 skb_free_head+0x93/0xb0 net/core/skbuff.c:592
 pskb_expand_head+0x2bd/0xff0 net/core/skbuff.c:1662
 netlink_trim+0x1fe/0x260 net/netlink/af_netlink.c:1284
 netlink_broadcast_filtered+0x67/0xd20 net/netlink/af_netlink.c:1489
 netlink_broadcast net/netlink/af_netlink.c:1534 [inline]
 nlmsg_multicast include/net/netlink.h:968 [inline]
 nlmsg_notify+0x93/0x250 net/netlink/af_netlink.c:2520
 nfnetlink_send+0x63/0x80 net/netfilter/nfnetlink.c:141
 nf_tables_flowtable_notify+0x22f/0x380 net/netfilter/nf_tables_api.c:6441
 nf_tables_commit+0x1137/0x3c90 net/netfilter/nf_tables_api.c:7184
 nfnetlink_rcv_batch+0xdb5/0x1780 net/netfilter/nfnetlink.c:485
 nfnetlink_rcv_skb_batch net/netfilter/nfnetlink.c:543 [inline]
 nfnetlink_rcv+0x3e7/0x460 net/netfilter/nfnetlink.c:561
 netlink_unicast_kernel net/netlink/af_netlink.c:1302 [inline]
 netlink_unicast+0x59e/0x7e0 net/netlink/af_netlink.c:1328
 netlink_sendmsg+0x91c/0xea0 net/netlink/af_netlink.c:1917
 sock_sendmsg_nosec net/socket.c:652 [inline]
 sock_sendmsg+0xd7/0x130 net/socket.c:672
 ____sys_sendmsg+0x753/0x880 net/socket.c:2343
 ___sys_sendmsg+0x100/0x170 net/socket.c:2397
 __sys_sendmsg+0x105/0x1d0 net/socket.c:2430
 __do_sys_sendmsg net/socket.c:2439 [inline]
 __se_sys_sendmsg net/socket.c:2437 [inline]
 __x64_sys_sendmsg+0x78/0xb0 net/socket.c:2437
 do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x49/0xbe

The buggy address belongs to the object at ffff88804eb50000
 which belongs to the cache kmalloc-8k of size 8192
The buggy address is located 8144 bytes inside of
 8192-byte region [ffff88804eb50000, ffff88804eb52000)
The buggy address belongs to the page:
page:ffffea00013ad400 refcount:1 mapcount:0 mapping:ffff8880aa4021c0 index:0x0 compound_mapcount: 0
flags: 0xfffe0000010200(slab|head)
raw: 00fffe0000010200 ffffea00013ad308 ffffea00013b6c08 ffff8880aa4021c0
raw: 0000000000000000 ffff88804eb50000 0000000100000001 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff88804eb51e80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff88804eb51f00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff88804eb51f80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
                                                 ^
 ffff88804eb52000: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff88804eb52080: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================

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