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

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: ca04b3cca11a Merge tag 'armsoc-fixes' of git://git.kernel...
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1609e968400000
kernel config: https://syzkaller.appspot.com/x/.config?x=2ca6c7a31d407f86
dashboard link: https://syzkaller.appspot.com/bug?extid=65c6b72f284a39d416b4
compiler: gcc (GCC) 8.0.1 20180413 (experimental)
syzkaller repro:https://syzkaller.appspot.com/x/repro.syz?x=1704f6d0400000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=17188a78400000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+65c6b7...@syzkaller.appspotmail.com

random: sshd: uninitialized urandom read (32 bytes read)
random: sshd: uninitialized urandom read (32 bytes read)
random: sshd: uninitialized urandom read (32 bytes read)
random: sshd: uninitialized urandom read (32 bytes read)
==================================================================
BUG: KASAN: slab-out-of-bounds in memcpy include/linux/string.h:345 [inline]
BUG: KASAN: slab-out-of-bounds in pdu_read+0x90/0xd0 net/9p/protocol.c:59
Read of size 62219 at addr ffff8801c9e904ed by task syz-executor251/4548

CPU: 0 PID: 4548 Comm: syz-executor251 Not tainted 4.18.0-rc3+ #137
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+0x1c9/0x2b4 lib/dump_stack.c:113
print_address_description+0x6c/0x20b mm/kasan/report.c:256
kasan_report_error mm/kasan/report.c:354 [inline]
kasan_report.cold.7+0x242/0x2fe mm/kasan/report.c:412
check_memory_region_inline mm/kasan/kasan.c:260 [inline]
check_memory_region+0x13e/0x1b0 mm/kasan/kasan.c:267
memcpy+0x23/0x50 mm/kasan/kasan.c:302
memcpy include/linux/string.h:345 [inline]
pdu_read+0x90/0xd0 net/9p/protocol.c:59
p9pdu_vreadf net/9p/protocol.c:162 [inline]
p9pdu_readf+0x579/0x2170 net/9p/protocol.c:536
p9_client_version net/9p/client.c:986 [inline]
p9_client_create+0xde0/0x16c9 net/9p/client.c:1069
v9fs_session_init+0x21a/0x1a80 fs/9p/v9fs.c:400
v9fs_mount+0x7c/0x900 fs/9p/vfs_super.c:135
mount_fs+0xae/0x328 fs/super.c:1277
vfs_kern_mount.part.34+0xdc/0x4e0 fs/namespace.c:1037
vfs_kern_mount fs/namespace.c:1027 [inline]
do_new_mount fs/namespace.c:2518 [inline]
do_mount+0x581/0x30e0 fs/namespace.c:2848
ksys_mount+0x12d/0x140 fs/namespace.c:3064
__do_sys_mount fs/namespace.c:3078 [inline]
__se_sys_mount fs/namespace.c:3075 [inline]
__x64_sys_mount+0xbe/0x150 fs/namespace.c:3075
do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x440319
Code: 18 89 d0 c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 00 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 fb 13 fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007ffdfd76d4e8 EFLAGS: 00000206 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 0030656c69662f2e RCX: 0000000000440319
RDX: 0000000020000140 RSI: 0000000020000100 RDI: 0000000000000000
RBP: 69736f7030707070 R08: 0000000020000280 R09: 0000000000000001
R10: 0000000000010000 R11: 0000000000000206 R12: 4c50473070707028
R13: 64663d736e617274 R14: 0000000000000000 R15: 0000000000000000

Allocated by task 4548:
save_stack+0x43/0xd0 mm/kasan/kasan.c:448
set_track mm/kasan/kasan.c:460 [inline]
kasan_kmalloc+0xc4/0xe0 mm/kasan/kasan.c:553
__do_kmalloc mm/slab.c:3718 [inline]
__kmalloc+0x14e/0x760 mm/slab.c:3727
kmalloc include/linux/slab.h:518 [inline]
p9_fcall_alloc+0x1e/0x90 net/9p/client.c:236
p9_tag_alloc net/9p/client.c:306 [inline]
p9_client_prepare_req.part.8+0x754/0xcd0 net/9p/client.c:722
p9_client_prepare_req net/9p/client.c:757 [inline]
p9_client_rpc+0x1bd/0x1400 net/9p/client.c:757
p9_client_version net/9p/client.c:976 [inline]
p9_client_create+0xd09/0x16c9 net/9p/client.c:1069
v9fs_session_init+0x21a/0x1a80 fs/9p/v9fs.c:400
v9fs_mount+0x7c/0x900 fs/9p/vfs_super.c:135
mount_fs+0xae/0x328 fs/super.c:1277
vfs_kern_mount.part.34+0xdc/0x4e0 fs/namespace.c:1037
vfs_kern_mount fs/namespace.c:1027 [inline]
do_new_mount fs/namespace.c:2518 [inline]
do_mount+0x581/0x30e0 fs/namespace.c:2848
ksys_mount+0x12d/0x140 fs/namespace.c:3064
__do_sys_mount fs/namespace.c:3078 [inline]
__se_sys_mount fs/namespace.c:3075 [inline]
__x64_sys_mount+0xbe/0x150 fs/namespace.c:3075
do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 0:
(stack is not available)

The buggy address belongs to the object at ffff8801c9e904c0
which belongs to the cache kmalloc-16384 of size 16384
The buggy address is located 45 bytes inside of
16384-byte region [ffff8801c9e904c0, ffff8801c9e944c0)
The buggy address belongs to the page:
page:ffffea000727a400 count:1 mapcount:0 mapping:ffff8801da802200 index:0x0
compound_mapcount: 0
flags: 0x2fffc0000008100(slab|head)
raw: 02fffc0000008100 ffffea0006d88408 ffff8801da801c48 ffff8801da802200
raw: 0000000000000000 ffff8801c9e904c0 0000000100000001 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff8801c9e92380: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
ffff8801c9e92400: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> ffff8801c9e92480: 00 00 00 00 00 00 00 00 00 00 00 00 fc fc fc fc
^
ffff8801c9e92500: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff8801c9e92580: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================


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