[syzbot] [ext4?] KASAN: use-after-free Read in ext4_find_extent (3)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 8a28a0b6f1a1 Merge tag 'net-6.4-rc8' of git://git.kernel.o..
git tree: upstream
console+strace: https://syzkaller.appspot.com/x/log.txt?x=12f5b40b280000
kernel config: https://syzkaller.appspot.com/x/.config?x=e74b395fe4978721
dashboard link: https://syzkaller.appspot.com/bug?extid=7ec4ebe875a7076ebb31
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=15a2b5c0a80000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1181c5c0a80000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/1e2a94b42e4e/disk-8a28a0b6.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/7b1e26b25d39/vmlinux-8a28a0b6.xz
kernel image: https://storage.googleapis.com/syzbot-assets/bd8294ebd044/bzImage-8a28a0b6.xz
mounted in repro #1: https://storage.googleapis.com/syzbot-assets/52d75ce070c3/mount_0.gz
mounted in repro #2: https://storage.googleapis.com/syzbot-assets/8168124ab578/mount_5.gz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+7ec4eb...@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: use-after-free in ext4_ext_binsearch fs/ext4/extents.c:837 [inline]
BUG: KASAN: use-after-free in ext4_find_extent+0xbc8/0xde0 fs/ext4/extents.c:953
Read of size 4 at addr ffff888073caa838 by task syz-executor976/4999

CPU: 0 PID: 4999 Comm: syz-executor976 Not tainted 6.4.0-rc7-syzkaller-00194-g8a28a0b6f1a1 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/27/2023
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:351 [inline]
print_report+0x163/0x540 mm/kasan/report.c:462
kasan_report+0x176/0x1b0 mm/kasan/report.c:572
ext4_ext_binsearch fs/ext4/extents.c:837 [inline]
ext4_find_extent+0xbc8/0xde0 fs/ext4/extents.c:953
ext4_ext_map_blocks+0x2d1/0x7210 fs/ext4/extents.c:4102
ext4_map_blocks+0xa4c/0x1cf0 fs/ext4/inode.c:623
_ext4_get_block+0x238/0x6a0 fs/ext4/inode.c:779
__block_write_begin_int+0x548/0x1a50 fs/buffer.c:2064
__block_write_begin fs/buffer.c:2114 [inline]
block_page_mkwrite+0x2fc/0x620 fs/buffer.c:2588
ext4_page_mkwrite+0x4ff/0x1290 fs/ext4/inode.c:6142
do_page_mkwrite+0x1a4/0x600 mm/memory.c:2931
wp_page_shared mm/memory.c:3280 [inline]
do_wp_page+0x501/0x3690 mm/memory.c:3362
handle_pte_fault mm/memory.c:4964 [inline]
__handle_mm_fault mm/memory.c:5089 [inline]
handle_mm_fault+0x2371/0x5860 mm/memory.c:5243
do_user_addr_fault arch/x86/mm/fault.c:1440 [inline]
handle_page_fault arch/x86/mm/fault.c:1534 [inline]
exc_page_fault+0x7d2/0x910 arch/x86/mm/fault.c:1590
asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:570
RIP: 0033:0x7f4b17ab09d5
Code: 73 00 e9 06 f8 ff ff 66 c7 04 25 00 01 00 20 2e 00 e9 28 f8 ff ff b8 00 36 00 20 48 8d 35 0b 4e 0a 00 b9 25 00 00 00 48 89 c7 <f3> 48 a5 0f b6 06 88 07 e9 38 f8 ff ff 50 b9 00 36 00 20 ba ac 04
RSP: 002b:00007ffcb22cf580 EFLAGS: 00010246
RAX: 0000000020003600 RBX: 00007ffcb22cf5b8 RCX: 0000000000000025
RDX: 40854a4c23aebd1f RSI: 00007f4b17b557d8 RDI: 0000000020003600
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 00000000ffffffff R11: 0000000000000246 R12: 00007ffcb22cf5b0
R13: 0000000000000000 R14: 431bde82d7b634db R15: 0000000000000000
</TASK>

The buggy address belongs to the physical page:
page:ffffea0001cf2a80 refcount:0 mapcount:0 mapping:0000000000000000 index:0x1 pfn:0x73caa
flags: 0xfff00000000000(node=0|zone=1|lastcpupid=0x7ff)
page_type: 0xffffffff()
raw: 00fff00000000000 ffffea0001cf2ac8 ffffea0001cf2a48 0000000000000000
raw: 0000000000000001 0000000000000000 00000000ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as freed
page last allocated via order 0, migratetype Movable, gfp_mask 0x140dca(GFP_HIGHUSER_MOVABLE|__GFP_COMP|__GFP_ZERO), pid 4990, tgid 4990 (sshd), ts 67865553810, free_ts 68052578311
set_page_owner include/linux/page_owner.h:31 [inline]
post_alloc_hook+0x1e6/0x210 mm/page_alloc.c:1731
prep_new_page mm/page_alloc.c:1738 [inline]
get_page_from_freelist+0x321c/0x33a0 mm/page_alloc.c:3502
__alloc_pages+0x255/0x670 mm/page_alloc.c:4768
__folio_alloc+0x13/0x30 mm/page_alloc.c:4800
vma_alloc_folio+0x48a/0x9a0 mm/mempolicy.c:2240
do_anonymous_page mm/memory.c:4085 [inline]
do_pte_missing mm/memory.c:3645 [inline]
handle_pte_fault mm/memory.c:4947 [inline]
__handle_mm_fault mm/memory.c:5089 [inline]
handle_mm_fault+0x2942/0x5860 mm/memory.c:5243
do_user_addr_fault arch/x86/mm/fault.c:1349 [inline]
handle_page_fault arch/x86/mm/fault.c:1534 [inline]
exc_page_fault+0x274/0x910 arch/x86/mm/fault.c:1590
asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:570
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+0x903/0xa30 mm/page_alloc.c:2564
free_unref_page_list+0x596/0x830 mm/page_alloc.c:2705
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
exit_mmap+0x3da/0xaf0 mm/mmap.c:3120
__mmput+0x115/0x3c0 kernel/fork.c:1351
exit_mm+0x227/0x310 kernel/exit.c:567
do_exit+0x612/0x2290 kernel/exit.c:861
do_group_exit+0x206/0x2c0 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+0x3f/0x40 kernel/exit.c:1033
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:
ffff888073caa700: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
ffff888073caa780: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff888073caa800: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
^
ffff888073caa880: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
ffff888073caa900: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
==================================================================


---
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[Theodore Ts'o]

#syz set prio: low

On Tue, Jun 27, 2023 at 09:16:56AM -0700, syzbot wrote:
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit: 8a28a0b6f1a1 Merge tag 'net-6.4-rc8' of git://git.kernel.o..
> git tree: upstream
> console+strace: https://syzkaller.appspot.com/x/log.txt?x=12f5b40b280000
> kernel config: https://syzkaller.appspot.com/x/.config?x=e74b395fe4978721
> dashboard link: https://syzkaller.appspot.com/bug?extid=7ec4ebe875a7076ebb31
> 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=15a2b5c0a80000
> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1181c5c0a80000

This report is via writing to the block device, while the file system
is mounted.

- Ted

[syzbot]

syzbot suspects this issue was fixed by commit:

commit 6f861765464f43a71462d52026fbddfc858239a5
Author: Jan Kara <ja...@suse.cz>
Date: Wed Nov 1 17:43:10 2023 +0000

fs: Block writes to mounted block devices

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=17b36eefe80000
start commit: c42d9eeef8e5 Merge tag 'hardening-v6.7-rc2' of git://git.k..
git tree: upstream
kernel config: https://syzkaller.appspot.com/x/.config?x=d05dd66e2eb2c872
dashboard link: https://syzkaller.appspot.com/bug?extid=7ec4ebe875a7076ebb31
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1585ea50e80000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=157ef53f680000

If the result looks correct, please mark the issue as fixed by replying with:

#syz fix: fs: Block writes to mounted block devices

For information about bisection process see: https://goo.gl/tpsmEJ#bisection

[Theodore Ts'o]