On Thu, Oct 17, 2019 at 10:08 AM Ronnie Sahlberg <lsahlber@xxxxxxxxxx> wrote:
>
> List, Pavel,
>
> So I think there are two bugs we need to fix in this small block to make it safe against a race against other threads calling cifs_delete_mid() and similar.
>
> We need to to protect the list mutate functions and wrap them inside the GlobalMid_Lock mutex
> but we can not hold this lock across the callback call.
>
> But we still need to protect the mid_entry dereference and the ->callback call against the mid structure being freed
> by DeleteMidQEntry(). We can do that by taking out an extra reference to the mid while holding the GlobalMid_Lock
> and then dropping the reference again after the callback completes.
>
>
> I think something like this might work :
>
>
>
> diff --git a/fs/cifs/connect.c b/fs/cifs/connect.c
> index bdea4b3e8005..3a1a9b63bd9b 100644
> --- a/fs/cifs/connect.c
> +++ b/fs/cifs/connect.c
> @@ -572,11 +572,19 @@ cifs_reconnect(struct TCP_Server_Info *server)
> mutex_unlock(&server->srv_mutex);
>
> cifs_dbg(FYI, "%s: issuing mid callbacks\n", __func__);
> + spin_lock(&GlobalMid_Lock);
> list_for_each_safe(tmp, tmp2, &retry_list) {
> mid_entry = list_entry(tmp, struct mid_q_entry, qhead);
I think you need a reference before this and something like
if (mid->mid_flags ...) /* check for someone else already deleting it */
;
else
> list_del_init(&mid_entry->qhead);
I am still tracing and I do not see the root of the problem yet.
Unsurprisingly, it looks like a use after free though.
> + kref_get(&mid_entry->refcount);
> + spin_unlock(&GlobalMid_Lock);
> +
> mid_entry->callback(mid_entry);
> + cifs_mid_q_entry_release(mid_entry);
> +
> + spin_lock(&GlobalMid_Lock);
> }
> + spin_unlock(&GlobalMid_Lock);
>
> if (cifs_rdma_enabled(server)) {
> mutex_lock(&server->srv_mutex);
>
>
> Pavel, can you have a look at this and comment? It is very delicate code so it needs careful review.
>
>
> regards
> ronnie sahlberg
>
>
>
> ----- Original Message -----
> From: "David Wysochanski" <dwysocha@xxxxxxxxxx>
> To: "Ronnie Sahlberg" <lsahlber@xxxxxxxxxx>
> Cc: "linux-cifs" <linux-cifs@xxxxxxxxxxxxxxx>, "Frank Sorenson" <sorenson@xxxxxxxxxx>
> Sent: Thursday, 17 October, 2019 9:42:08 PM
> Subject: Re: list_del corruption while iterating retry_list in cifs_reconnect still seen on 5.4-rc3
>
> On Thu, Oct 17, 2019 at 5:05 AM Ronnie Sahlberg <lsahlber@xxxxxxxxxx> wrote:
> >
> >
> >
> > > > 575--> list_for_each_safe(tmp, tmp2, &retry_list) {
> > > > 576 mid_entry = list_entry(tmp, struct mid_q_entry, qhead);
> > > > 577 list_del_init(&mid_entry->qhead);
> > > > 578 mid_entry->callback(mid_entry);
> > > > 579 }
> >
> > This part (and a similar loop during shutting down the demultiplex thread) is the only place
> > where we add/remove to the ->qhead list without holding the GlobalMid_Lock.
> >
> > I wonder if it is racing against a different thread also modifying qhead for the same mid,
> > like cifs_delete_mid() for example.
> >
>
> Yes I agree, I was thinking along these same lines of reasoning as I
> read the code. I put the latest on the investigation into the bug:
> https://bugzilla.redhat.com/show_bug.cgi?id=1654538#c15
>
> Just before the crash, when we hit the iteration of retry_list
> something has gone wrong - the very first mid_entry on retry_list is a
> garbage address, when normally it should be the last address from the
> previous call to list_move in the loop above it.
>
>
> ----- Original Message -----
> > > From: "Ronnie Sahlberg" <lsahlber@xxxxxxxxxx>
> > > To: "David Wysochanski" <dwysocha@xxxxxxxxxx>
> > > Cc: "linux-cifs" <linux-cifs@xxxxxxxxxxxxxxx>, "Frank Sorenson" <sorenson@xxxxxxxxxx>
> > > Sent: Thursday, 17 October, 2019 10:17:18 AM
> > > Subject: Re: list_del corruption while iterating retry_list in cifs_reconnect still seen on 5.4-rc3
> > >
> > > I can not reproduce this :-(
> > >
> > > I have run it for a few hours, restarting samba in a loop with up to 30
> > > threads.
> > >
>
> I am not sure if it helps but I have 8 CPUs on my VM.
> I also have server signing and client signing mandatory.
> I can send you the smb.conf offline.
>
>
> > >
> > > Can you check
> > > 1, If this only reproduce for you for the root of the share or it also
> > > reproduces for a subdirectory?
> > > 2, Does it reproduce also if you use "nohandlecache" mount option?
> > > This disables the use of cached open of the root handle, i.e.
> > > open_shroot()
> > > 3, When this happens, can you check the content of the mid entry and what
> > > these fields are:
> > > mid->mid_flags, mid->handle (this is a function pointer, what does it
> > > point to)
> > > mid->command. Maybe print the whole structure.
> > >
>
> Ok I'll see what I can find out. So far I am not sure I have
> identified what else is touching the mid in between the two loops.
>
> > > regards
> > > ronnie sahlberg
> > >
> > >
> > >
> > >
> > > ----- Original Message -----
> > > > From: "David Wysochanski" <dwysocha@xxxxxxxxxx>
> > > > To: "linux-cifs" <linux-cifs@xxxxxxxxxxxxxxx>
> > > > Cc: "Frank Sorenson" <sorenson@xxxxxxxxxx>
> > > > Sent: Thursday, 17 October, 2019 5:27:02 AM
> > > > Subject: list_del corruption while iterating retry_list in cifs_reconnect
> > > > still seen on 5.4-rc3
> > > >
> > > > I think this has been there for a long time, since we first saw this
> > > > on a 4.18.0 based kernel but I just noticed the bug recently.
> > > > I just retested on 5.4-rc3 and it's still there. Easy to repro with a
> > > > fairly simple but invasive server restart test - takes only maybe a
> > > > couple minutes on my VM.
> > > >
> > > >
> > > > From Frank Sorenson:
> > > >
> > > > mount off a samba server:
> > > >
> > > > # mount //vm1/share /mnt/vm1
> > > > -overs=2.1,hard,sec=ntlmssp,credentials=/root/.smb_creds
> > > >
> > > >
> > > > on the client, start 10 'find' loops:
> > > >
> > > > # export test_path=/mnt/vm1
> > > > # do_find() { while true ; do find $test_path >/dev/null 2>&1 ; done }
> > > >
> > > > # for i in {1..10} ; do do_find & done
> > > >
> > > >
> > > > optional: also start something to monitor for when the hang occurs:
> > > >
> > > > # while true ; do count=$(grep smb2_reconnect /proc/*/stack -A3 |
> > > > grep -c open_shroot) ; [[ $count -gt 0 ]] && { echo "$(date):
> > > > reproduced bug" ; break ; } ; echo "$(date): stayin' alive" ; sleep 2
> > > > ; done
> > > >
> > > >
> > > >
> > > > On the samba server: restart smb.service (loop it in case it requires
> > > > more than one restart):
> > > >
> > > > # while true ; do echo "$(date): restarting" ; systemctl restart
> > > > smb.service ; sleep 5 ; done | tee /var/tmp/smb_restart_log.out
> > > >
> > > >
> > > >
> > > >
> > > > [ 430.454897] list_del corruption. prev->next should be
> > > > ffff98d3a8f316c0, but was 2e885cb266355469
> > > > [ 430.464668] ------------[ cut here ]------------
> > > > [ 430.466569] kernel BUG at lib/list_debug.c:51!
> > > > [ 430.468476] invalid opcode: 0000 [#1] SMP PTI
> > > > [ 430.470286] CPU: 0 PID: 13267 Comm: cifsd Kdump: loaded Not tainted
> > > > 5.4.0-rc3+ #19
> > > > [ 430.473472] Hardware name: Red Hat KVM, BIOS 0.5.1 01/01/2011
> > > > [ 430.475872] RIP: 0010:__list_del_entry_valid.cold+0x31/0x55
> > > > [ 430.478129] Code: 5e 15 8e e8 54 a3 c5 ff 0f 0b 48 c7 c7 78 5f 15
> > > > 8e e8 46 a3 c5 ff 0f 0b 48 89 f2 48 89 fe 48 c7 c7 38 5f 15 8e e8 32
> > > > a3 c5 ff <0f> 0b 48 89 fe 4c 89 c2 48 c7 c7 00 5f 15 8e e8 1e a3 c5 ff
> > > > 0f 0b
> > > > [ 430.485563] RSP: 0018:ffffb4db0042fd38 EFLAGS: 00010246
> > > > [ 430.487665] RAX: 0000000000000054 RBX: ffff98d3aabb8800 RCX:
> > > > 0000000000000000
> > > > [ 430.490513] RDX: 0000000000000000 RSI: ffff98d3b7a17908 RDI:
> > > > ffff98d3b7a17908
> > > > [ 430.493383] RBP: ffff98d3a8f316c0 R08: ffff98d3b7a17908 R09:
> > > > 0000000000000285
> > > > [ 430.496258] R10: ffffb4db0042fbf0 R11: ffffb4db0042fbf5 R12:
> > > > ffff98d3aabb89c0
> > > > [ 430.499113] R13: ffffb4db0042fd48 R14: 2e885cb266355469 R15:
> > > > ffff98d3b24c4480
> > > > [ 430.501981] FS: 0000000000000000(0000) GS:ffff98d3b7a00000(0000)
> > > > knlGS:0000000000000000
> > > > [ 430.505232] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > > > [ 430.507546] CR2: 00007f08cd17b9c0 CR3: 000000023484a000 CR4:
> > > > 00000000000406f0
> > > > [ 430.510426] Call Trace:
> > > > [ 430.511500] cifs_reconnect+0x25e/0x610 [cifs]
> > > > [ 430.513350] cifs_readv_from_socket+0x220/0x250 [cifs]
> > > > [ 430.515464] cifs_read_from_socket+0x4a/0x70 [cifs]
> > > > [ 430.517452] ? try_to_wake_up+0x212/0x650
> > > > [ 430.519122] ? cifs_small_buf_get+0x16/0x30 [cifs]
> > > > [ 430.521086] ? allocate_buffers+0x66/0x120 [cifs]
> > > > [ 430.523019] cifs_demultiplex_thread+0xdc/0xc30 [cifs]
> > > > [ 430.525116] kthread+0xfb/0x130
> > > > [ 430.526421] ? cifs_handle_standard+0x190/0x190 [cifs]
> > > > [ 430.528514] ? kthread_park+0x90/0x90
> > > > [ 430.530019] ret_from_fork+0x35/0x40
> > > > [ 430.531487] Modules linked in: cifs libdes libarc4 ip6t_rpfilter
> > > > ip6t_REJECT nf_reject_ipv6 xt_conntrack ebtable_nat ip6table_nat
> > > > ip6table_mangle ip6table_raw ip6table_security iptable_nat nf_nat
> > > > iptable_mangle iptable_raw iptable_security nf_conntrack
> > > > nf_defrag_ipv6 nf_defrag_ipv4 ip_set nfnetlink ebtable_filter ebtables
> > > > ip6table_filter ip6_tables crct10dif_pclmul crc32_pclmul joydev
> > > > virtio_balloon ghash_clmulni_intel i2c_piix4 nfsd nfs_acl lockd
> > > > auth_rpcgss grace sunrpc xfs libcrc32c virtio_net net_failover
> > > > crc32c_intel virtio_console serio_raw virtio_blk ata_generic failover
> > > > pata_acpi qemu_fw_cfg
> > > > [ 430.552782] ---[ end trace c91d4468f8689482 ]---
> > > > [ 430.554948] RIP: 0010:__list_del_entry_valid.cold+0x31/0x55
> > > > [ 430.557251] Code: 5e 15 8e e8 54 a3 c5 ff 0f 0b 48 c7 c7 78 5f 15
> > > > 8e e8 46 a3 c5 ff 0f 0b 48 89 f2 48 89 fe 48 c7 c7 38 5f 15 8e e8 32
> > > > a3 c5 ff <0f> 0b 48 89 fe 4c 89 c2 48 c7 c7 00 5f 15 8e e8 1e a3 c5 ff
> > > > 0f 0b
> > > > [ 430.565019] RSP: 0018:ffffb4db0042fd38 EFLAGS: 00010246
> > > > [ 430.567181] RAX: 0000000000000054 RBX: ffff98d3aabb8800 RCX:
> > > > 0000000000000000
> > > > [ 430.570073] RDX: 0000000000000000 RSI: ffff98d3b7a17908 RDI:
> > > > ffff98d3b7a17908
> > > > [ 430.572955] RBP: ffff98d3a8f316c0 R08: ffff98d3b7a17908 R09:
> > > > 0000000000000285
> > > > [ 430.575854] R10: ffffb4db0042fbf0 R11: ffffb4db0042fbf5 R12:
> > > > ffff98d3aabb89c0
> > > > [ 430.578745] R13: ffffb4db0042fd48 R14: 2e885cb266355469 R15:
> > > > ffff98d3b24c4480
> > > > [ 430.581624] FS: 0000000000000000(0000) GS:ffff98d3b7a00000(0000)
> > > > knlGS:0000000000000000
> > > > [ 430.584881] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > > > [ 430.587230] CR2: 00007f08cd17b9c0 CR3: 000000023484a000 CR4:
> > > > 00000000000406f0
> > > >
> > > >
> > > > crash> dis -lr cifs_reconnect+0x25e | tail --lines=20
> > > > 0xffffffffc062dc26 <cifs_reconnect+0x226>: movb
> > > > $0x0,0xbb36b(%rip) # 0xffffffffc06e8f98 <GlobalMid_Lock>
> > > > /mnt/build/kernel/fs/cifs/connect.c: 572
> > > > 0xffffffffc062dc2d <cifs_reconnect+0x22d>: mov %r12,%rdi
> > > > 0xffffffffc062dc30 <cifs_reconnect+0x230>: callq
> > > > 0xffffffff8d9d5a20 <mutex_unlock>
> > > > /mnt/build/kernel/fs/cifs/connect.c: 574
> > > > 0xffffffffc062dc35 <cifs_reconnect+0x235>: testb
> > > > $0x1,0xbb300(%rip) # 0xffffffffc06e8f3c <cifsFYI>
> > > > 0xffffffffc062dc3c <cifs_reconnect+0x23c>: je
> > > > 0xffffffffc062dc43 <cifs_reconnect+0x243>
> > > > /mnt/build/kernel/./arch/x86/include/asm/jump_label.h: 25
> > > > 0xffffffffc062dc3e <cifs_reconnect+0x23e>: data32 data32 data32
> > > > xchg %ax,%ax
> > > > /mnt/build/kernel/fs/cifs/connect.c: 575
> > > > 0xffffffffc062dc43 <cifs_reconnect+0x243>: mov 0x8(%rsp),%rbp
> > > > 0xffffffffc062dc48 <cifs_reconnect+0x248>: mov 0x0(%rbp),%r14
> > > > 0xffffffffc062dc4c <cifs_reconnect+0x24c>: cmp %r13,%rbp
> > > > 0xffffffffc062dc4f <cifs_reconnect+0x24f>: jne
> > > > 0xffffffffc062dc56 <cifs_reconnect+0x256>
> > > > 0xffffffffc062dc51 <cifs_reconnect+0x251>: jmp
> > > > 0xffffffffc062dc90 <cifs_reconnect+0x290>
> > > > 0xffffffffc062dc53 <cifs_reconnect+0x253>: mov %rax,%r14
> > > > /mnt/build/kernel/./include/linux/list.h: 190
> > > > 0xffffffffc062dc56 <cifs_reconnect+0x256>: mov %rbp,%rdi
> > > > 0xffffffffc062dc59 <cifs_reconnect+0x259>: callq
> > > > 0xffffffff8d4e6b00 <__list_del_entry_valid>
> > > > 0xffffffffc062dc5e <cifs_reconnect+0x25e>: test %al,%al
> > > >
> > > >
> > > > fs/cifs/connect.c
> > > > 566 mid_entry = list_entry(tmp, struct mid_q_entry, qhead);
> > > > 567 if (mid_entry->mid_state == MID_REQUEST_SUBMITTED)
> > > > 568 mid_entry->mid_state = MID_RETRY_NEEDED;
> > > > 569 list_move(&mid_entry->qhead, &retry_list);
> > > > 570 }
> > > > 571 spin_unlock(&GlobalMid_Lock);
> > > > 572 mutex_unlock(&server->srv_mutex);
> > > > 573
> > > > 574 cifs_dbg(FYI, "%s: issuing mid callbacks\n", __func__);
> > > > 575--> list_for_each_safe(tmp, tmp2, &retry_list) {
> > > > 576 mid_entry = list_entry(tmp, struct mid_q_entry, qhead);
> > > > 577 list_del_init(&mid_entry->qhead);
> > > > 578 mid_entry->callback(mid_entry);
> > > > 579 }
> > > > 580
> > > > 581 if (cifs_rdma_enabled(server)) {
> > > > 582 mutex_lock(&server->srv_mutex);
> > > > 583 smbd_destroy(server);
> > > > 584 mutex_unlock(&server->srv_mutex);
> > > >
> > >
>
>
>
> --
> Dave Wysochanski
> Principal Software Maintenance Engineer
> T: 919-754-4024
--
Dave Wysochanski
Principal Software Maintenance Engineer
T: 919-754-4024
