[syzbot] [net?] KASAN: stack-out-of-bounds Read in skb_splice_from_iter

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: e7c5433c5aaa tools: ynl: Remove duplicated include in hand..
git tree: net-next
console+strace: https://syzkaller.appspot.com/x/log.txt?x=109d3d1d280000
kernel config: https://syzkaller.appspot.com/x/.config?x=526f919910d4a671
dashboard link: https://syzkaller.appspot.com/bug?extid=d8486855ef44506fd675
compiler: gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=10f22943280000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=13e1363b280000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/13c08af1fd21/disk-e7c5433c.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/35820511752b/vmlinux-e7c5433c.xz
kernel image: https://storage.googleapis.com/syzbot-assets/6a8cbec0d40f/bzImage-e7c5433c.xz

The issue was bisected to:

commit 2dc334f1a63a8839b88483a3e73c0f27c9c1791c
Author: David Howells <dhow...@redhat.com>
Date: Wed Jun 7 18:19:09 2023 +0000

splice, net: Use sendmsg(MSG_SPLICE_PAGES) rather than ->sendpage()

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=149e0c8b280000
final oops: https://syzkaller.appspot.com/x/report.txt?x=169e0c8b280000
console output: https://syzkaller.appspot.com/x/log.txt?x=129e0c8b280000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+d84868...@syzkaller.appspotmail.com
Fixes: 2dc334f1a63a ("splice, net: Use sendmsg(MSG_SPLICE_PAGES) rather than ->sendpage()")

==================================================================
BUG: KASAN: stack-out-of-bounds in skb_splice_from_iter+0xcd6/0xd70 net/core/skbuff.c:6933
Read of size 8 at addr ffffc900039bf8f8 by task syz-executor193/5001

CPU: 1 PID: 5001 Comm: syz-executor193 Not tainted 6.4.0-rc5-syzkaller-00915-ge7c5433c5aaa #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/25/2023
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0xd9/0x150 lib/dump_stack.c:106
print_address_description.constprop.0+0x2c/0x3c0 mm/kasan/report.c:351
print_report mm/kasan/report.c:462 [inline]
kasan_report+0x11c/0x130 mm/kasan/report.c:572
skb_splice_from_iter+0xcd6/0xd70 net/core/skbuff.c:6933
__ip_append_data+0x1439/0x3c20 net/ipv4/ip_output.c:1210
ip_append_data net/ipv4/ip_output.c:1350 [inline]
ip_append_data+0x115/0x1a0 net/ipv4/ip_output.c:1329
raw_sendmsg+0xb50/0x30a0 net/ipv4/raw.c:641
inet_sendmsg+0x9d/0xe0 net/ipv4/af_inet.c:829
sock_sendmsg_nosec net/socket.c:724 [inline]
sock_sendmsg+0xde/0x190 net/socket.c:747
splice_to_socket+0x954/0xe30 fs/splice.c:917
do_splice_from fs/splice.c:969 [inline]
do_splice+0xb8c/0x1e50 fs/splice.c:1309
__do_splice+0x14e/0x270 fs/splice.c:1387
__do_sys_splice fs/splice.c:1598 [inline]
__se_sys_splice fs/splice.c:1580 [inline]
__x64_sys_splice+0x19c/0x250 fs/splice.c:1580
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x39/0xb0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x63/0xcd
RIP: 0033:0x7fba0bf36d29
Code: 28 c3 e8 2a 14 00 00 66 2e 0f 1f 84 00 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 73 01 c3 48 c7 c1 c0 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffe0d4bac38 EFLAGS: 00000246 ORIG_RAX: 0000000000000113
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007fba0bf36d29
RDX: 0000000000000005 RSI: 0000000000000000 RDI: 0000000000000003
RBP: 00007fba0befaed0 R08: 000000000004ffdd R09: 000000000000000d
R10: 0000000000000000 R11: 0000000000000246 R12: 00007fba0befaf60
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
</TASK>

The buggy address belongs to stack of task syz-executor193/5001
and is located at offset 408 in frame:
raw_sendmsg+0x0/0x30a0 include/net/sock.h:2733

This frame has 8 objects:
[48, 52) 'hdrincl'
[64, 68) 'err'
[80, 88) 'rt'
[112, 152) 'ipc'
[192, 240) 'state'
[272, 336) 'fl4'
[368, 392) 'rfv'
[432, 504) 'opt_copy'

The buggy address belongs to the virtual mapping at
[ffffc900039b8000, ffffc900039c1000) created by:
kernel_clone+0xeb/0x890 kernel/fork.c:2915

The buggy address belongs to the physical page:
page:ffffea0001d6c880 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x75b22
flags: 0xfff00000000000(node=0|zone=1|lastcpupid=0x7ff)
page_type: 0xffffffff()
raw: 00fff00000000000 0000000000000000 dead000000000122 0000000000000000
raw: 0000000000000000 0000000000000000 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 0, migratetype Unmovable, gfp_mask 0x2dc2(GFP_KERNEL|__GFP_HIGHMEM|__GFP_NOWARN|__GFP_ZERO), pid 4968, tgid 4968 (dhcpcd-run-hook), ts 47435778840, free_ts 47434086594
set_page_owner include/linux/page_owner.h:31 [inline]
post_alloc_hook+0x2db/0x350 mm/page_alloc.c:1731
prep_new_page mm/page_alloc.c:1738 [inline]
get_page_from_freelist+0xf41/0x2c00 mm/page_alloc.c:3502
__alloc_pages+0x1cb/0x4a0 mm/page_alloc.c:4768
alloc_pages+0x1aa/0x270 mm/mempolicy.c:2279
vm_area_alloc_pages mm/vmalloc.c:3009 [inline]
__vmalloc_area_node mm/vmalloc.c:3085 [inline]
__vmalloc_node_range+0xb1c/0x14a0 mm/vmalloc.c:3257
alloc_thread_stack_node kernel/fork.c:313 [inline]
dup_task_struct kernel/fork.c:1116 [inline]
copy_process+0x13bb/0x75c0 kernel/fork.c:2333
kernel_clone+0xeb/0x890 kernel/fork.c:2915
__do_sys_clone+0xba/0x100 kernel/fork.c:3058
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x39/0xb0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x63/0xcd
page last free stack trace:
reset_page_owner include/linux/page_owner.h:24 [inline]
free_pages_prepare mm/page_alloc.c:1302 [inline]
free_unref_page_prepare+0x62e/0xcb0 mm/page_alloc.c:2564
free_unref_page_list+0xe3/0xa70 mm/page_alloc.c:2705
release_pages+0xcd8/0x1380 mm/swap.c:1042
tlb_batch_pages_flush+0xa8/0x1a0 mm/mmu_gather.c:97
tlb_flush_mmu_free mm/mmu_gather.c:292 [inline]
tlb_flush_mmu mm/mmu_gather.c:299 [inline]
tlb_finish_mmu+0x14b/0x7e0 mm/mmu_gather.c:391
exit_mmap+0x2b2/0x930 mm/mmap.c:3123
__mmput+0x128/0x4c0 kernel/fork.c:1351
mmput+0x60/0x70 kernel/fork.c:1373
exit_mm kernel/exit.c:567 [inline]
do_exit+0x9b0/0x29b0 kernel/exit.c:861
do_group_exit+0xd4/0x2a0 kernel/exit.c:1024
__do_sys_exit_group kernel/exit.c:1035 [inline]
__se_sys_exit_group kernel/exit.c:1033 [inline]
__x64_sys_exit_group+0x3e/0x50 kernel/exit.c:1033
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x39/0xb0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x63/0xcd

Memory state around the buggy address:
ffffc900039bf780: f1 f1 04 f2 00 00 00 f2 f2 f2 00 00 00 00 00 f2
ffffc900039bf800: f2 f2 f2 f2 00 00 00 00 00 00 f2 f2 f2 f2 00 00
>ffffc900039bf880: 00 00 00 00 00 00 f2 f2 f2 f2 00 00 00 f2 f2 f2
^
ffffc900039bf900: f2 f2 00 00 00 00 00 00 00 00 00 f3 f3 f3 f3 f3
ffffc900039bf980: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
==================================================================


---
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If the bug is already fixed, let syzbot know by replying with:
#syz fix: exact-commit-title

If you want syzbot to run the reproducer, reply with:
#syz test: git://repo/address.git branch-or-commit-hash
If you attach or paste a git patch, syzbot will apply it before testing.

If you want to change bug's subsystems, reply with:
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If the bug is a duplicate of another bug, reply with:
#syz dup: exact-subject-of-another-report

If you want to undo deduplication, reply with:
#syz undup

[Jakub Kicinski]

Hi David, are you fighting all these fires reported by syzbot?
I see another one just rolled in from yesterdays KCM changes.

[David Howells]

Jakub Kicinski <ku...@kernel.org> wrote:

> Hi David, are you fighting all these fires reported by syzbot?
> I see another one just rolled in from yesterdays KCM changes.

I'm trying to pin down a bug in the old DIO code whilst attending the AFS
Workshop. I'll get to the sendpage reports in a bit. I think a bunch of them
are probably the same issue in AF_ALG hashing. They do at least have
reproducers.

David

[David Howells]

#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next.git main

commit b49195695a78f1fb56ecbfd3c3fd14dbe6844088
Author: David Howells <dhow...@redhat.com>
Date: Wed Jun 14 00:14:32 2023 +0100

ip, ip6: Handle splice to raw and ping sockets

Splicing to SOCK_RAW sockets may set MSG_SPLICE_PAGES, but in such a case,
__ip_append_data() will call skb_splice_from_iter() to access the 'from'
data, assuming it to point to a msghdr struct with an iter, instead of
using the provided getfrag function to access it.

In the case of raw_sendmsg(), however, this is not the case and 'from' will
point to a raw_frag_vec struct and raw_getfrag() will be the frag-getting
function. A similar issue may occur with rawv6_sendmsg().

Fix this by ignoring MSG_SPLICE_PAGES if getfrag != ip_generic_getfrag as
ip_generic_getfrag() expects "from" to be a msghdr*, but the other getfrags
don't. Note that this will prevent MSG_SPLICE_PAGES from being effective
for udplite.

This likely affects ping sockets too. udplite looks like it should be okay
as it expects "from" to be a msghdr.

Signed-off-by: David Howells <dhow...@redhat.com>
Reported-by: syzbot+d84868...@syzkaller.appspotmail.com
Link: https://lore.kernel.org/r/000000000000ae...@google.com/

Fixes: 2dc334f1a63a ("splice, net: Use sendmsg(MSG_SPLICE_PAGES) rather than ->sendpage()")

cc: Willem de Bruijn <willemdebr...@gmail.com>
cc: David Ahern <dsa...@kernel.org>
cc: "David S. Miller" <da...@davemloft.net>
cc: Eric Dumazet <edum...@google.com>
cc: Jakub Kicinski <ku...@kernel.org>
cc: Paolo Abeni <pab...@redhat.com>
cc: Jens Axboe <ax...@kernel.dk>
cc: Matthew Wilcox <wi...@infradead.org>
cc: net...@vger.kernel.org

diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
index 244fb9365d87..4b39ea99f00b 100644
--- a/net/ipv4/ip_output.c
+++ b/net/ipv4/ip_output.c
@@ -1040,7 +1040,8 @@ static int __ip_append_data(struct sock *sk,
} else if ((flags & MSG_SPLICE_PAGES) && length) {
if (inet->hdrincl)
return -EPERM;
- if (rt->dst.dev->features & NETIF_F_SG)
+ if (rt->dst.dev->features & NETIF_F_SG &&
+ getfrag == ip_generic_getfrag)
/* We need an empty buffer to attach stuff to */
paged = true;
else
diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
index c722cb881b2d..dd845139882c 100644
--- a/net/ipv6/ip6_output.c
+++ b/net/ipv6/ip6_output.c
@@ -1592,7 +1592,8 @@ static int __ip6_append_data(struct sock *sk,
} else if ((flags & MSG_SPLICE_PAGES) && length) {
if (inet_sk(sk)->hdrincl)
return -EPERM;
- if (rt->dst.dev->features & NETIF_F_SG)
+ if (rt->dst.dev->features & NETIF_F_SG &&
+ getfrag == ip_generic_getfrag)
/* We need an empty buffer to attach stuff to */
paged = true;
else

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-and-tested-by: syzbot+d84868...@syzkaller.appspotmail.com

Tested on:

commit: a9c47697 Merge branch 'tools-ynl-gen-improvements-for-..
git tree: git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next.git main
console output: https://syzkaller.appspot.com/x/log.txt?x=145cfc8b280000

kernel config: https://syzkaller.appspot.com/x/.config?x=526f919910d4a671
dashboard link: https://syzkaller.appspot.com/bug?extid=d8486855ef44506fd675
compiler: gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2

patch: https://syzkaller.appspot.com/x/patch.diff?x=14ed8d2d280000

Note: testing is done by a robot and is best-effort only.