Message-ID: <104766d8-7429-4ba5-8b3b-bbbd0244c6e3@collabora.com>
Date:   Thu, 7 Sep 2023 18:27:03 +0500
From:   Muhammad Usama Anjum <usama.anjum@...labora.com>
To:     syzbot <syzbot+6e5f2db05775244c73b7@...kaller.appspotmail.com>,
        adilger.kernel@...ger.ca, Theodore Ts'o <tytso@....edu>,
        Allison Henderson <achender@...ibm.com>,
        Alex Tomas <alex@...sterfs.com>
Cc:     Muhammad Usama Anjum <usama.anjum@...labora.com>,
        linux-fsdevel@...r.kernel.org, syzkaller-bugs@...glegroups.com,
        linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [syzbot] [ext4?] KASAN: out-of-bounds Read in
 ext4_ext_remove_space

On 9/7/23 5:56 PM, Muhammad Usama Anjum wrote:
> On 7/14/23 4:50 PM, syzbot wrote:
>> Hello,
>>
>> syzbot found the following issue on:
>>
>> HEAD commit: 06c2afb862f9 Linux 6.5-rc1
>> git tree: upstream
>> console output: https://syzkaller.appspot.com/x/log.txt?x=13d550a2a80000
>> kernel config: https://syzkaller.appspot.com/x/.config?x=29fd3392a08741ef
>> dashboard link: https://syzkaller.appspot.com/bug?extid=6e5f2db05775244c73b7
>> compiler: Debian clang version 15.0.7, GNU ld (GNU Binutils for Debian) 2.35.2
>> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=11fc4702a80000
>> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=172a98eca80000
> The last crash on upstream/mainline happened at e6fda526d9db. On the latest
> mainline 7ba2090ca64ea, there is no crash. I've searched on mailing lists
Just tested mainline with syzbot, the issue got triggered:
https://groups.google.com/g/syzkaller-bugs/c/G6zS-LKgDW0/m/wwiAavVlBQAJ

There must be some race condition which wasn't triggering on mainline for me.

> if some fix has been merged. I've not found anything. The same bug is
> present on LTS kernels.
> 
> In fs/ext4/extents.c:
> 
> memmove(ex, ex+1,
> 	(EXT_LAST_EXTENT(eh) - ex) * sizeof(struct ext4_extent));
> 
> When crash happens:
> EXT_LAST_EXTENT(eh) = 0xFFFF888130260000
> ex = 0xFFFF88813026006C
> 
> These are wrong values. EXT_LAST_EXTENT(eh) - ex results in negative value
> as ex is bigger. The bigger ex is bug in itself. ex is the member of this
> list with header eh. Any help would be much appreciated.
> 
>>
>> Downloadable assets:
>> disk image: https://storage.googleapis.com/syzbot-assets/b66ebf11f3d4/disk-06c2afb8.raw.xz
>> vmlinux: https://storage.googleapis.com/syzbot-assets/e277ce7d54f6/vmlinux-06c2afb8.xz
>> kernel image: https://storage.googleapis.com/syzbot-assets/5d0b981e9278/bzImage-06c2afb8.xz
>> mounted in repro: https://storage.googleapis.com/syzbot-assets/c48fda4748ae/mount_0.gz
>>
>> IMPORTANT: if you fix the issue, please add the following tag to the commit:
>> Reported-by: syzbot+6e5f2db05775244c73b7@...kaller.appspotmail.com
>>
>> EXT4-fs error (device loop0) in ext4_mb_clear_bb:6537: Corrupt filesystem
>> ==================================================================
>> BUG: KASAN: out-of-bounds in ext4_ext_rm_leaf fs/ext4/extents.c:2736 [inline]
>> BUG: KASAN: out-of-bounds in ext4_ext_remove_space+0x2482/0x4d90 fs/ext4/extents.c:2958
>> Read of size 18446744073709551508 at addr ffff888073aea078 by task syz-executor420/6443
>>
>> CPU: 1 PID: 6443 Comm: syz-executor420 Not tainted 6.5.0-rc1-syzkaller #0
>> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/03/2023
>> Call Trace:
>> <TASK>
>> __dump_stack lib/dump_stack.c:88 [inline]
>> dump_stack_lvl+0x1e7/0x2d0 lib/dump_stack.c:106
>> print_address_description mm/kasan/report.c:364 [inline]
>> print_report+0x163/0x540 mm/kasan/report.c:475
>> kasan_report+0x175/0x1b0 mm/kasan/report.c:588
>> kasan_check_range+0x27e/0x290 mm/kasan/generic.c:187
>> __asan_memmove+0x29/0x70 mm/kasan/shadow.c:94
>> ext4_ext_rm_leaf fs/ext4/extents.c:2736 [inline]
>> ext4_ext_remove_space+0x2482/0x4d90 fs/ext4/extents.c:2958
>> ext4_punch_hole+0x7a0/0xc10 fs/ext4/inode.c:3977
>> ext4_fallocate+0x311/0x1f90 fs/ext4/extents.c:4706
>> vfs_fallocate+0x551/0x6b0 fs/open.c:324
>> do_vfs_ioctl+0x22cb/0x2b30 fs/ioctl.c:849
>> __do_sys_ioctl fs/ioctl.c:868 [inline]
>> __se_sys_ioctl+0x81/0x170 fs/ioctl.c:856
>> 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
>> RIP: 0033:0x7ff03605dce9
>> Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 a1 15 00 00 90 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 b8 ff ff ff f7 d8 64 89 01 48
>> RSP: 002b:00007ff02dc072f8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
>> RAX: ffffffffffffffda RBX: 00007ff0360e27c0 RCX: 00007ff03605dce9
>> RDX: 0000000020000080 RSI: 000000004030582b RDI: 0000000000000004
>> RBP: 00007ff0360af678 R08: 00007ff02dc07700 R09: 0000000000000000
>> R10: 00007ff02dc07700 R11: 0000000000000246 R12: 65766f6365726f6e
>> R13: 0031656c69662f2e R14: 6f6f6c2f7665642f R15: 00007ff0360e27c8
>> </TASK>
>>
>> The buggy address belongs to the physical page:
>> page:ffffea0001ceba80 refcount:2 mapcount:0 mapping:ffff88801e21cd80 index:0x2b pfn:0x73aea
>> memcg:ffff888141652000
>> aops:def_blk_aops ino:700000
>> flags: 0xfff00000002036(referenced|uptodate|lru|active|private|node=0|zone=1|lastcpupid=0x7ff)
>> page_type: 0xffffffff()
>> raw: 00fff00000002036 ffffea0001c164c8 ffffea0001f600c8 ffff88801e21cd80
>> raw: 000000000000002b ffff8880729c1d98 00000002ffffffff ffff888141652000
>> page dumped because: kasan: bad access detected
>> page_owner tracks the page as allocated
>> page last allocated via order 0, migratetype Movable, gfp_mask 0x148c48(GFP_NOFS|__GFP_NOFAIL|__GFP_COMP|__GFP_HARDWALL|__GFP_MOVABLE), pid 6428, tgid 6426 (syz-executor420), ts 165572616396, free_ts 165556735464
>> set_page_owner include/linux/page_owner.h:31 [inline]
>> post_alloc_hook+0x1e6/0x210 mm/page_alloc.c:1570
>> prep_new_page mm/page_alloc.c:1577 [inline]
>> get_page_from_freelist+0x31e8/0x3370 mm/page_alloc.c:3221
>> __alloc_pages+0x255/0x670 mm/page_alloc.c:4477
>> folio_alloc+0x1e/0x60 mm/mempolicy.c:2289
>> filemap_alloc_folio+0xde/0x500 mm/filemap.c:979
>> __filemap_get_folio+0x323/0xa00 mm/filemap.c:1933
>> grow_dev_page fs/buffer.c:1063 [inline]
>> grow_buffers fs/buffer.c:1123 [inline]
>> __getblk_slow fs/buffer.c:1150 [inline]
>> __getblk_gfp+0x218/0x630 fs/buffer.c:1445
>> sb_getblk_gfp include/linux/buffer_head.h:376 [inline]
>> ext4_ext_grow_indepth fs/ext4/extents.c:1334 [inline]
>> ext4_ext_create_new_leaf fs/ext4/extents.c:1435 [inline]
>> ext4_ext_insert_extent+0xfe3/0x4e60 fs/ext4/extents.c:2102
>> ext4_ext_map_blocks+0x1bdc/0x71d0 fs/ext4/extents.c:4306
>> ext4_map_blocks+0xa2f/0x1cb0 fs/ext4/inode.c:621
>> _ext4_get_block+0x238/0x6a0 fs/ext4/inode.c:763
>> ext4_block_write_begin+0x53d/0x1570 fs/ext4/inode.c:1043
>> ext4_write_begin+0x619/0x10b0
>> ext4_da_write_begin+0x300/0xa40 fs/ext4/inode.c:2867
>> generic_perform_write+0x31b/0x630 mm/filemap.c:3923
>> ext4_buffered_write_iter+0xc6/0x350 fs/ext4/file.c:299
>> page last free stack trace:
>> reset_page_owner include/linux/page_owner.h:24 [inline]
>> free_pages_prepare mm/page_alloc.c:1161 [inline]
>> free_unref_page_prepare+0x903/0xa30 mm/page_alloc.c:2348
>> free_unref_page_list+0x596/0x830 mm/page_alloc.c:2489
>> release_pages+0x2193/0x2470 mm/swap.c:1042
>> tlb_batch_pages_flush mm/mmu_gather.c:97 [inline]
>> tlb_flush_mmu_free mm/mmu_gather.c:292 [inline]
>> tlb_flush_mmu+0x100/0x210 mm/mmu_gather.c:299
>> tlb_finish_mmu+0xd4/0x1f0 mm/mmu_gather.c:391
>> unmap_region+0x258/0x2a0 mm/mmap.c:2317
>> do_vmi_align_munmap+0x135d/0x1630 mm/mmap.c:2556
>> do_vmi_munmap+0x24d/0x2d0 mm/mmap.c:2623
>> __vm_munmap+0x230/0x450 mm/mmap.c:2905
>> __do_sys_munmap mm/mmap.c:2922 [inline]
>> __se_sys_munmap mm/mmap.c:2919 [inline]
>> __x64_sys_munmap+0x69/0x80 mm/mmap.c:2919
>> 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
>>
>> Memory state around the buggy address:
>> ffff888073ae9f00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>> ffff888073ae9f80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>>> ffff888073aea000: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>> ^
>> ffff888073aea080: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>> ffff888073aea100: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>> ==================================================================
>>
>>
>> ---
>> This report is generated by a bot. It may contain errors.
>> See https://goo.gl/tpsmEJ for more information about syzbot.
>> syzbot engineers can be reached at syzkaller@...glegroups.com.
>>
>> syzbot will keep track of this issue. See:
>> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
>>
>> 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:
>> #syz set subsystems: new-subsystem
>> (See the list of subsystem names on the web dashboard)
>>
>> 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
> 

-- 
BR,
Muhammad Usama Anjum

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