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

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: bd6bf7c10484 Merge tag 'pci-v4.20-changes' of git://git.ke..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=16fd6bcb400000
kernel config: https://syzkaller.appspot.com/x/.config?x=2dd8629d56664133
dashboard link: https://syzkaller.appspot.com/bug?extid=5da0d0a72a9e7d791748
compiler: gcc (GCC) 8.0.1 20180413 (experimental)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=16b3ea33400000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=17f9f1bd400000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+5da0d0...@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: slab-out-of-bounds in sctp_getsockopt_pr_streamstatus
net/sctp/socket.c:7174 [inline]
BUG: KASAN: slab-out-of-bounds in sctp_getsockopt+0x7516/0x7cc2
net/sctp/socket.c:7582
Read of size 8 at addr ffff8801d89f0968 by task syz-executor278/5330

CPU: 1 PID: 5330 Comm: syz-executor278 Not tainted 4.19.0+ #303
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+0x244/0x39d lib/dump_stack.c:113
print_address_description.cold.7+0x9/0x1ff mm/kasan/report.c:256
kasan_report_error mm/kasan/report.c:354 [inline]
kasan_report.cold.8+0x242/0x309 mm/kasan/report.c:412
__asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:433
sctp_getsockopt_pr_streamstatus net/sctp/socket.c:7174 [inline]
sctp_getsockopt+0x7516/0x7cc2 net/sctp/socket.c:7582
sock_common_getsockopt+0x9a/0xe0 net/core/sock.c:2937
__sys_getsockopt+0x1ad/0x390 net/socket.c:1939
__do_sys_getsockopt net/socket.c:1950 [inline]
__se_sys_getsockopt net/socket.c:1947 [inline]
__x64_sys_getsockopt+0xbe/0x150 net/socket.c:1947
do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x445789
Code: e8 6c b6 02 00 48 83 c4 18 c3 0f 1f 80 00 00 00 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 2b 12 fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007effdb293db8 EFLAGS: 00000246 ORIG_RAX: 0000000000000037
RAX: ffffffffffffffda RBX: 00000000006dac48 RCX: 0000000000445789
RDX: 0000000000000074 RSI: 0000000000000084 RDI: 0000000000000003
RBP: 00000000006dac40 R08: 0000000020000040 R09: 0000000000000000
R10: 0000000020000080 R11: 0000000000000246 R12: 00000000006dac4c
R13: 00007ffcfc408c6f R14: 00007effdb2949c0 R15: 00000000006dad2c

Allocated by task 5329:
save_stack+0x43/0xd0 mm/kasan/kasan.c:448
set_track mm/kasan/kasan.c:460 [inline]
kasan_kmalloc+0xc7/0xe0 mm/kasan/kasan.c:553
kmem_cache_alloc_trace+0x152/0x750 mm/slab.c:3620
kmalloc include/linux/slab.h:513 [inline]
kzalloc include/linux/slab.h:707 [inline]
sctp_stream_init_ext+0x4f/0xf0 net/sctp/stream.c:237
sctp_sendmsg_to_asoc+0x1308/0x1a20 net/sctp/socket.c:1896
sctp_sendmsg+0x13c2/0x1da0 net/sctp/socket.c:2113
inet_sendmsg+0x1a1/0x690 net/ipv4/af_inet.c:798
sock_sendmsg_nosec net/socket.c:621 [inline]
sock_sendmsg+0xd5/0x120 net/socket.c:631
__sys_sendto+0x3d7/0x670 net/socket.c:1788
__do_sys_sendto net/socket.c:1800 [inline]
__se_sys_sendto net/socket.c:1796 [inline]
__x64_sys_sendto+0xe1/0x1a0 net/socket.c:1796
do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 3223:
save_stack+0x43/0xd0 mm/kasan/kasan.c:448
set_track mm/kasan/kasan.c:460 [inline]
__kasan_slab_free+0x102/0x150 mm/kasan/kasan.c:521
kasan_slab_free+0xe/0x10 mm/kasan/kasan.c:528
__cache_free mm/slab.c:3498 [inline]
kfree+0xcf/0x230 mm/slab.c:3813
kzfree+0x28/0x30 mm/slab_common.c:1543
aa_free_file_ctx security/apparmor/include/file.h:76 [inline]
apparmor_file_free_security+0x133/0x1a0 security/apparmor/lsm.c:448
security_file_free+0x4a/0x80 security/security.c:900
file_free fs/file_table.c:54 [inline]
__fput+0x4e8/0xa30 fs/file_table.c:294
____fput+0x15/0x20 fs/file_table.c:309
task_work_run+0x1e8/0x2a0 kernel/task_work.c:113
tracehook_notify_resume include/linux/tracehook.h:188 [inline]
exit_to_usermode_loop+0x318/0x380 arch/x86/entry/common.c:166
prepare_exit_to_usermode arch/x86/entry/common.c:197 [inline]
syscall_return_slowpath arch/x86/entry/common.c:268 [inline]
do_syscall_64+0x6be/0x820 arch/x86/entry/common.c:293
entry_SYSCALL_64_after_hwframe+0x49/0xbe

The buggy address belongs to the object at ffff8801d89f0900
which belongs to the cache kmalloc-96 of size 96
The buggy address is located 8 bytes to the right of
96-byte region [ffff8801d89f0900, ffff8801d89f0960)
The buggy address belongs to the page:
page:ffffea0007627c00 count:1 mapcount:0 mapping:ffff8801da8004c0 index:0x0
flags: 0x2fffc0000000100(slab)
raw: 02fffc0000000100 ffffea0007646748 ffffea0007613488 ffff8801da8004c0
raw: 0000000000000000 ffff8801d89f0000 0000000100000020 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff8801d89f0800: fb fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc
ffff8801d89f0880: fb fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc
> ffff8801d89f0900: 00 00 00 00 00 00 00 00 00 00 00 fc fc fc fc fc
^
ffff8801d89f0980: fb fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc
ffff8801d89f0a00: fb fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc
==================================================================


---
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[Xin Long]

On Sat, Oct 27, 2018 at 1:38 AM syzbot
<syzbot+5da0d0...@syzkaller.appspotmail.com> wrote:
>
> Hello,
>
> syzbot found the following crash on:
>
> HEAD commit: bd6bf7c10484 Merge tag 'pci-v4.20-changes' of git://git.ke..
> git tree: upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=16fd6bcb400000
> kernel config: https://syzkaller.appspot.com/x/.config?x=2dd8629d56664133
> dashboard link: https://syzkaller.appspot.com/bug?extid=5da0d0a72a9e7d791748
> compiler: gcc (GCC) 8.0.1 20180413 (experimental)
> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=16b3ea33400000
> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=17f9f1bd400000
>
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+5da0d0...@syzkaller.appspotmail.com
>
> ==================================================================
> BUG: KASAN: slab-out-of-bounds in sctp_getsockopt_pr_streamstatus
> net/sctp/socket.c:7174 [inline]

Forgot to change to use "&" in sctp_getsockopt_pr_streamstatus() in
"sctp: get pr_assoc and pr_stream all status with SCTP_PR_SCTP_ALL instead"

@@ -7158,7 +7158,7 @@ static int
sctp_getsockopt_pr_streamstatus(struct sock *sk, int len,
goto out;
}

- if (policy == SCTP_PR_SCTP_ALL) {
+ if (policy & SCTP_PR_SCTP_ALL) {

[Marcelo Ricardo Leitner]

Hmmm. This is trying to avoid the
streamoute->abandoned_unsent[__SCTP_PR_INDEX(policy)]
with possibly large 'policy' as policy may be SCTP_PR_SCTP_ALL | SCTP_PR_SCTP_MASK

That said, I don't think this is a good fix because the input
parameter was bogus and we would be trying to make some sense out of
it. So I suggest something along these lines:

diff --git a/net/sctp/socket.c b/net/sctp/socket.c
index fc0386e8ff23..b816956c69f5 100644
--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c
@@ -7144,6 +7144,8 @@ static int sctp_getsockopt_pr_streamstatus(struct sock *sk, int len,
policy = params.sprstat_policy;
if (!policy || (policy & ~(SCTP_PR_SCTP_MASK | SCTP_PR_SCTP_ALL)))
goto out;
+ if (policy & SCTP_PR_SCTP_ALL && policy & ~SCTP_PR_SCTP_ALL)
+ goto out;

asoc = sctp_id2assoc(sk, params.sprstat_assoc_id);
if (!asoc || params.sprstat_sid >= asoc->stream.outcnt)

To bail out if ALL is specificied together with anything else.
(the if condition probably could be optimized somehow)

[Xin Long]

sure, will change to:
@@ -7142,7 +7148,8 @@ static int

sctp_getsockopt_pr_streamstatus(struct sock *sk, int len,
}

policy = params.sprstat_policy;

- if (!policy || (policy & ~(SCTP_PR_SCTP_MASK | SCTP_PR_SCTP_ALL)))
+ if (!policy || (policy & ~(SCTP_PR_SCTP_MASK | SCTP_PR_SCTP_ALL)) ||
+ ((policy & SCTP_PR_SCTP_ALL) && (policy & SCTP_PR_SCTP_MASK)))
goto out;

including the one in sctp_getsockopt_pr_assocstatus(), thanks.