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Date: Fri, 23 Jun 2023 08:48:05 -0500
From: Dave Kleikamp <dave.kleikamp@...cle.com>
To: Immad Mir <mirimmad17@...il.com>
Cc: Immad Mir <mirimmad@...look.com>,
"skhan@...uxfoundation.org" <skhan@...uxfoundation.org>,
"syzbot+f1faa20eec55e0c8644c@...kaller.appspotmail.com"
<syzbot+f1faa20eec55e0c8644c@...kaller.appspotmail.com>,
"jfs-discussion@...ts.sourceforge.net"
<jfs-discussion@...ts.sourceforge.net>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] FS: JFS: Fix null-ptr-deref Read in txBegin
On 6/23/23 8:40AM, Immad Mir wrote:
> Thanks for the feedback. I've prepared two patches to fix the bug.
>
> >Does this test case attempt to remount a read-only file system as
> read-write? I see a potential bug there.
> I'm not really sure about this.
>
> > Should be setting rc to an error here. I suggest -EROFS, but anything
> is better than returning zero. Calling jfs_error() might also be in
> order, as that would explicitly mark the file system to read-only. (The
> default behavior at least.)
>
> I've incorporated your suggested changes.
>
> > It'd be nice if we could move the check to txBegin(), but it is
> assumed to always succeed, so there's no good error recovery there
> without changing all of the callers. Maybe we can call jfs_error() there
> in case we get there from another syscall.
>
> I am not sure what to do here. I am calling jfs_error and returning 0
> which is not what the caller would expect.
jfs_error returns void. What it does is mark the superblock dirty and
either panics, marks sets the filesystem read-only, or does nothing
else, depending on a mount flag which I doubt anyone uses, so the
default action is to set it read-only. You still have to set a return
code, etc. after calling it.
I'm sorry I wasn't more specific the first time.
>
> Thanks,
> Immad.
>
>
> On Thu, Jun 22, 2023 at 8:38 PM Dave Kleikamp <dave.kleikamp@...cle.com
> <mailto:dave.kleikamp@...cle.com>> wrote:
>
> On 6/20/23 10:53PM, Immad Mir wrote:
>
>>
>>
>> Hi. May I please request a review on this patch.
>
> Sorry for the delay. See below.
>
>>
>> Thanks,
>> Immad
>>
>> ------------------------------------------------------------------------
>> *From:* mirimmad@...look.com <mailto:mirimmad@...look.com>
>> <mirimmad@...look.com> <mailto:mirimmad@...look.com>
>> *Sent:* Sunday, March 26, 2023 9:51:15 PM
>> *Cc:* mirimmad@...look.com <mailto:mirimmad@...look.com>
>> <mirimmad@...look.com> <mailto:mirimmad@...look.com>;
>> skhan@...uxfoundation.org <mailto:skhan@...uxfoundation.org>
>> <skhan@...uxfoundation.org> <mailto:skhan@...uxfoundation.org>;
>> Immad Mir <mirimmad17@...il.com> <mailto:mirimmad17@...il.com>;
>> syzbot+f1faa20eec55e0c8644c@...kaller.appspotmail.com
>> <mailto:syzbot+f1faa20eec55e0c8644c@...kaller.appspotmail.com>
>> <syzbot+f1faa20eec55e0c8644c@...kaller.appspotmail.com>
>> <mailto:syzbot+f1faa20eec55e0c8644c@...kaller.appspotmail.com>;
>> Dave Kleikamp <shaggy@...nel.org> <mailto:shaggy@...nel.org>;
>> jfs-discussion@...ts.sourceforge.net
>> <mailto:jfs-discussion@...ts.sourceforge.net>
>> <jfs-discussion@...ts.sourceforge.net>
>> <mailto:jfs-discussion@...ts.sourceforge.net>;
>> linux-kernel@...r.kernel.org <mailto:linux-kernel@...r.kernel.org>
>> <linux-kernel@...r.kernel.org> <mailto:linux-kernel@...r.kernel.org>
>> *Subject:* [PATCH] FS: JFS: Fix null-ptr-deref Read in txBegin
>>
>> From: Immad Mir <mirimmad17@...il.com> <mailto:mirimmad17@...il.com>
>>
>> syzkaller reported the following issue:
>>
>> BUG: KASAN: null-ptr-deref in instrument_atomic_read
>> include/linux/instrumented.h:72 [inline]
>> BUG: KASAN: null-ptr-deref in _test_bit
>> include/asm-generic/bitops/instrumented-non-atomic.h:141 [inline]
>> BUG: KASAN: null-ptr-deref in txBegin+0x131/0x6c0
>> fs/jfs/jfs_txnmgr.c:366
>> Read of size 8 at addr 0000000000000040 by task syz-executor.0/5098
>>
>> CPU: 0 PID: 5098 Comm: syz-executor.0 Not tainted
>> 6.3.0-rc3-syzkaller-00005-g7d31677bb7b1 #0
>> Hardware name: Google Compute Engine/Google Compute Engine, BIOS
>> Google 03/02/2023
>> Call Trace:
>> <TASK>
>> __dump_stack lib/dump_stack.c:88 [inline]
>> dump_stack_lvl+0x1e7/0x2d0 lib/dump_stack.c:106
>> print_report+0xe6/0x540 mm/kasan/report.c:433
>> kasan_report+0x176/0x1b0 mm/kasan/report.c:536
>> kasan_check_range+0x283/0x290 mm/kasan/generic.c:187
>> instrument_atomic_read include/linux/instrumented.h:72 [inline]
>> _test_bit
>> include/asm-generic/bitops/instrumented-non-atomic.h:141 [inline]
>> txBegin+0x131/0x6c0 fs/jfs/jfs_txnmgr.c:366
>> jfs_link+0x1ac/0x5e0 fs/jfs/namei.c:802
>> vfs_link+0x4ed/0x680 fs/namei.c:4522
>> do_linkat+0x5cc/0x9e0 fs/namei.c:4593
>> __do_sys_linkat fs/namei.c:4621 [inline]
>> __se_sys_linkat fs/namei.c:4618 [inline]
>> __x64_sys_linkat+0xdd/0xf0 fs/namei.c:4618
>> do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>> do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
>> entry_SYSCALL_64_after_hwframe+0x63/0xcd
>>
>> The issue can be resolved by checking whethere "log"
>> for a given superblock exists in the jfs_link function
>> before beginning a transaction.
>
> I'm not sure how we got here. log should only be null if the file
> system is mounted read-only. Does this test case attempt to remount
> a read-only file system as read-write? I see a potential bug there.
>
>>
>> Tested with syzbot.
>> Reported-by: syzbot+f1faa20eec55e0c8644c@...kaller.appspotmail.com
>> <mailto:syzbot+f1faa20eec55e0c8644c@...kaller.appspotmail.com>
>> Link:
>> https://syzkaller.appspot.com/bug?id=be7e52c50c5182cc09a09ea6fc456446b2039de3 <https://syzkaller.appspot.com/bug?id=be7e52c50c5182cc09a09ea6fc456446b2039de3>
>>
>> Signed-off-by: Immad Mir <mirimmad17@...il.com>
>> <mailto:mirimmad17@...il.com>
>> ---
>> fs/jfs/namei.c | 2 ++
>> 1 file changed, 2 insertions(+)
>>
>> diff --git a/fs/jfs/namei.c b/fs/jfs/namei.c
>> index b29d68b5e..cd43b68e2 100644
>> --- a/fs/jfs/namei.c
>> +++ b/fs/jfs/namei.c
>> @@ -799,6 +799,8 @@ static int jfs_link(struct dentry *old_dentry,
>> if (rc)
>> goto out;
>>
>> + if (!(JFS_SBI(ip->i_sb)->log))
>> + goto out;
>
> Should be setting rc to an error here. I suggest -EROFS, but
> anything is better than returning zero. Calling jfs_error() might
> also be in order, as that would explicitly mark the file system to
> read-only. (The default behavior at least.)
>
>> tid = txBegin(ip->i_sb, 0);
> It'd be nice if we could move the check to txBegin(), but it is
> assumed to always succeed, so there's no good error recovery there
> without changing all of the callers. Maybe we can call jfs_error()
> there in case we get there from another syscall.
>>
>> mutex_lock_nested(&JFS_IP(dir)->commit_mutex, COMMIT_MUTEX_PARENT);
>> --
>> 2.40.0
>>
>>
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