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Date:   Wed, 1 Nov 2023 09:46:36 -0500
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Subject: Re: [PATCH] UBSAN: array-index-out-of-bounds in dtSplitRoot
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To:     Osama Muhammad <osmtendev@gmail.com>
Cc:     jfs-discussion@lists.sourceforge.net, linux-kernel@vger.kernel.org,
        syzbot+d4b1df2e9d4ded6488ec@syzkaller.appspotmail.com
References: <20231013191028.17382-1-osmtendev@gmail.com>
From:   Dave Kleikamp <dave.kleikamp@oracle.com>
In-Reply-To: <20231013191028.17382-1-osmtendev@gmail.com>
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On 10/13/23 2:10PM, Osama Muhammad wrote:
> Syzkaller reported the following issue:
> 
> oop0: detected capacity change from 0 to 32768
> 
> UBSAN: array-index-out-of-bounds in fs/jfs/jfs_dtree.c:1971:9
> index -2 is out of range for type 'struct dtslot [128]'
> CPU: 0 PID: 3613 Comm: syz-executor270 Not tainted 6.0.0-syzkaller-09423-g493ffd6605b2 #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/22/2022
> Call Trace:
>   <TASK>
>   __dump_stack lib/dump_stack.c:88 [inline]
>   dump_stack_lvl+0x1b1/0x28e lib/dump_stack.c:106
>   ubsan_epilogue lib/ubsan.c:151 [inline]
>   __ubsan_handle_out_of_bounds+0xdb/0x130 lib/ubsan.c:283
>   dtSplitRoot+0x8d8/0x1900 fs/jfs/jfs_dtree.c:1971
>   dtSplitUp fs/jfs/jfs_dtree.c:985 [inline]
>   dtInsert+0x1189/0x6b80 fs/jfs/jfs_dtree.c:863
>   jfs_mkdir+0x757/0xb00 fs/jfs/namei.c:270
>   vfs_mkdir+0x3b3/0x590 fs/namei.c:4013
>   do_mkdirat+0x279/0x550 fs/namei.c:4038
>   __do_sys_mkdirat fs/namei.c:4053 [inline]
>   __se_sys_mkdirat fs/namei.c:4051 [inline]
>   __x64_sys_mkdirat+0x85/0x90 fs/namei.c:4051
>   do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>   do_syscall_64+0x3d/0xb0 arch/x86/entry/common.c:80
>   entry_SYSCALL_64_after_hwframe+0x63/0xcd
> RIP: 0033:0x7fcdc0113fd9
> Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 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:00007ffeb8bc67d8 EFLAGS: 00000246 ORIG_RAX: 0000000000000102
> RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007fcdc0113fd9
> RDX: 0000000000000000 RSI: 0000000020000340 RDI: 0000000000000003
> RBP: 00007fcdc00d37a0 R08: 0000000000000000 R09: 00007fcdc00d37a0
> R10: 00005555559a72c0 R11: 0000000000000246 R12: 00000000f8008000
> R13: 0000000000000000 R14: 00083878000000f8 R15: 0000000000000000
>   </TASK>
> 
> The issue is caused when the value of fsi becomes less than -1.
> The check to break the loop when fsi value becomes -1 is present
> but syzbot was able to produce value less than -1 which cause the error.
> This patch simply add the change for the values less than 0.
> 
> The patch is tested via syzbot.

Looks good.

Thanks,
Shaggy

> 
> Reported-and-tested-by: syzbot+d4b1df2e9d4ded6488ec@syzkaller.appspotmail.com
> Link: https://syzkaller.appspot.com/bug?extid=d4b1df2e9d4ded6488ec
> Signed-off-by: Osama Muhammad <osmtendev@gmail.com>
> ---
>   fs/jfs/jfs_dtree.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/jfs/jfs_dtree.c b/fs/jfs/jfs_dtree.c
> index 92b7c533407c..f3d3e8b3f50c 100644
> --- a/fs/jfs/jfs_dtree.c
> +++ b/fs/jfs/jfs_dtree.c
> @@ -1970,7 +1970,7 @@ static int dtSplitRoot(tid_t tid,
>   		do {
>   			f = &rp->slot[fsi];
>   			fsi = f->next;
> -		} while (fsi != -1);
> +		} while (fsi >= 0);
>   
>   		f->next = n;
>   	}