Message-ID: <68dc6b7f.050a0220.25d7ab.076b.GAE@google.com>
Date: Tue, 30 Sep 2025 16:45:03 -0700
From: syzbot <syzbot+9db318d6167044609878@...kaller.appspotmail.com>
To: kartikey406@...il.com, linux-kernel@...r.kernel.org, 
	syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [ext4?] KASAN: use-after-free Read in ext4_ext_insert_extent

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
KASAN: slab-out-of-bounds Read in ext4_ext_insert_extent

EXT4-fs (loop4): stripe (1570) is not aligned with cluster size (16), stripe is disabled
==================================================================
BUG: KASAN: slab-out-of-bounds in ext4_ext_insert_extent+0x41b6/0x4af0 fs/ext4/extents.c:2096
Read of size 4 at addr ffff88805b641c18 by task syz.4.165/7385

CPU: 0 UID: 0 PID: 7385 Comm: syz.4.165 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
Call Trace:
 <TASK>
 dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
 print_address_description mm/kasan/report.c:378 [inline]
 print_report+0xca/0x240 mm/kasan/report.c:482
 kasan_report+0x118/0x150 mm/kasan/report.c:595
 ext4_ext_insert_extent+0x41b6/0x4af0 fs/ext4/extents.c:2096
 ext4_ext_map_blocks+0x1bc9/0x3890 fs/ext4/extents.c:4420
 ext4_map_create_blocks fs/ext4/inode.c:609 [inline]
 ext4_map_blocks+0x860/0x1740 fs/ext4/inode.c:811
 _ext4_get_block+0x200/0x4c0 fs/ext4/inode.c:910
 ext4_get_block_unwritten+0x2e/0x100 fs/ext4/inode.c:943
 ext4_block_write_begin+0x993/0x1710 fs/ext4/inode.c:1198
 ext4_write_begin+0xc04/0x19a0 fs/ext4/ext4_jbd2.h:-1
 ext4_da_write_begin+0x445/0xda0 fs/ext4/inode.c:3129
 generic_perform_write+0x2c2/0x900 mm/filemap.c:4175
 ext4_buffered_write_iter+0xce/0x3a0 fs/ext4/file.c:299
 ext4_file_write_iter+0x298/0x1bc0 fs/ext4/file.c:-1
 new_sync_write fs/read_write.c:593 [inline]
 vfs_write+0x5c9/0xb30 fs/read_write.c:686
 ksys_pwrite64 fs/read_write.c:793 [inline]
 __do_sys_pwrite64 fs/read_write.c:801 [inline]
 __se_sys_pwrite64 fs/read_write.c:798 [inline]
 __x64_sys_pwrite64+0x193/0x220 fs/read_write.c:798
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fbff2b8e969
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 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fbff3a58038 EFLAGS: 00000246 ORIG_RAX: 0000000000000012
RAX: ffffffffffffffda RBX: 00007fbff2db5fa0 RCX: 00007fbff2b8e969
RDX: 000000000000fdef RSI: 0000200000000140 RDI: 0000000000000004
RBP: 00007fbff2c10ab1 R08: 0000000000000000 R09: 0000000000000000
R10: 000000000000fecc R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 00007fbff2db5fa0 R15: 00007ffc69cdac78
 </TASK>

Allocated by task 6339:
 kasan_save_stack mm/kasan/common.c:47 [inline]
 kasan_save_track+0x3e/0x80 mm/kasan/common.c:68
 poison_kmalloc_redzone mm/kasan/common.c:388 [inline]
 __kasan_kmalloc+0x93/0xb0 mm/kasan/common.c:405
 kasan_kmalloc include/linux/kasan.h:260 [inline]
 __do_kmalloc_node mm/slub.c:4376 [inline]
 __kvmalloc_node_noprof+0x30d/0x5f0 mm/slub.c:5067
 alloc_netdev_mqs+0xa3/0x11b0 net/core/dev.c:11812
 rtnl_create_link+0x31f/0xd10 net/core/rtnetlink.c:3633
 rtnl_newlink_create+0x25c/0xb00 net/core/rtnetlink.c:3815
 __rtnl_newlink net/core/rtnetlink.c:3942 [inline]
 rtnl_newlink+0x16d6/0x1c70 net/core/rtnetlink.c:4057
 rtnetlink_rcv_msg+0x7cf/0xb70 net/core/rtnetlink.c:6946
 netlink_rcv_skb+0x205/0x470 net/netlink/af_netlink.c:2552
 netlink_unicast_kernel net/netlink/af_netlink.c:1320 [inline]
 netlink_unicast+0x82c/0x9e0 net/netlink/af_netlink.c:1346
 netlink_sendmsg+0x805/0xb30 net/netlink/af_netlink.c:1896
 sock_sendmsg_nosec net/socket.c:714 [inline]
 __sock_sendmsg+0x21c/0x270 net/socket.c:729
 __sys_sendto+0x3bd/0x520 net/socket.c:2231
 __do_sys_sendto net/socket.c:2238 [inline]
 __se_sys_sendto net/socket.c:2234 [inline]
 __x64_sys_sendto+0xde/0x100 net/socket.c:2234
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

The buggy address belongs to the object at ffff88805b640000
 which belongs to the cache kmalloc-cg-4k of size 4096
The buggy address is located 3696 bytes to the right of
 allocated 3496-byte region [ffff88805b640000, ffff88805b640da8)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x5b640
head: order:3 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
memcg:ffff88802ed031c1
flags: 0xfff00000000040(head|node=0|zone=1|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 00fff00000000040 ffff88801a04b500 dead000000000122 0000000000000000
raw: 0000000000000000 0000000000040004 00000000f5000000 ffff88802ed031c1
head: 00fff00000000040 ffff88801a04b500 dead000000000122 0000000000000000
head: 0000000000000000 0000000000040004 00000000f5000000 ffff88802ed031c1
head: 00fff00000000003 ffffea00016d9001 00000000ffffffff 00000000ffffffff
head: ffffffffffffffff 0000000000000000 00000000ffffffff 0000000000000008
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 3, migratetype Unmovable, gfp_mask 0xd60c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_RETRY_MAYFAIL|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 6339, tgid 6339 (syz-executor), ts 122638337757, free_ts 82614727744
 set_page_owner include/linux/page_owner.h:32 [inline]
 post_alloc_hook+0x240/0x2a0 mm/page_alloc.c:1851
 prep_new_page mm/page_alloc.c:1859 [inline]
 get_page_from_freelist+0x21d5/0x22b0 mm/page_alloc.c:3858
 __alloc_frozen_pages_noprof+0x181/0x370 mm/page_alloc.c:5148
 alloc_pages_mpol+0x232/0x4a0 mm/mempolicy.c:2416
 alloc_slab_page mm/slub.c:2492 [inline]
 allocate_slab+0x8a/0x370 mm/slub.c:2660
 new_slab mm/slub.c:2714 [inline]
 ___slab_alloc+0xbeb/0x1420 mm/slub.c:3901
 __slab_alloc mm/slub.c:3992 [inline]
 __slab_alloc_node mm/slub.c:4067 [inline]
 slab_alloc_node mm/slub.c:4228 [inline]
 __do_kmalloc_node mm/slub.c:4375 [inline]
 __kvmalloc_node_noprof+0x429/0x5f0 mm/slub.c:5067
 alloc_netdev_mqs+0xa3/0x11b0 net/core/dev.c:11812
 rtnl_create_link+0x31f/0xd10 net/core/rtnetlink.c:3633
 rtnl_newlink_create+0x25c/0xb00 net/core/rtnetlink.c:3815
 __rtnl_newlink net/core/rtnetlink.c:3942 [inline]
 rtnl_newlink+0x16d6/0x1c70 net/core/rtnetlink.c:4057
 rtnetlink_rcv_msg+0x7cf/0xb70 net/core/rtnetlink.c:6946
 netlink_rcv_skb+0x205/0x470 net/netlink/af_netlink.c:2552
 netlink_unicast_kernel net/netlink/af_netlink.c:1320 [inline]
 netlink_unicast+0x82c/0x9e0 net/netlink/af_netlink.c:1346
 netlink_sendmsg+0x805/0xb30 net/netlink/af_netlink.c:1896
 sock_sendmsg_nosec net/socket.c:714 [inline]
 __sock_sendmsg+0x21c/0x270 net/socket.c:729
page last free pid 5876 tgid 5876 stack trace:
 reset_page_owner include/linux/page_owner.h:25 [inline]
 free_pages_prepare mm/page_alloc.c:1395 [inline]
 __free_frozen_pages+0xbb1/0xd20 mm/page_alloc.c:2895
 vfree+0x25a/0x400 mm/vmalloc.c:3434
 kcov_put kernel/kcov.c:439 [inline]
 kcov_close+0x28/0x50 kernel/kcov.c:535
 __fput+0x44c/0xa70 fs/file_table.c:468
 task_work_run+0x1d1/0x260 kernel/task_work.c:227
 exit_task_work include/linux/task_work.h:40 [inline]
 do_exit+0x6b5/0x2300 kernel/exit.c:961
 do_group_exit+0x21c/0x2d0 kernel/exit.c:1102
 get_signal+0x125e/0x1310 kernel/signal.c:3034
 arch_do_signal_or_restart+0x9a/0x750 arch/x86/kernel/signal.c:337
 exit_to_user_mode_loop+0x75/0x110 kernel/entry/common.c:40
 exit_to_user_mode_prepare include/linux/irq-entry-common.h:225 [inline]
 syscall_exit_to_user_mode_work include/linux/entry-common.h:175 [inline]
 syscall_exit_to_user_mode include/linux/entry-common.h:210 [inline]
 do_syscall_64+0x2bd/0x3b0 arch/x86/entry/syscall_64.c:100
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Memory state around the buggy address:
 ffff88805b641b00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff88805b641b80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff88805b641c00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
                            ^
 ffff88805b641c80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff88805b641d00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================


Tested on:

commit:         22bdd6e6 Merge tag 'x86_apic_for_v6.18_rc1' of git://g..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=108366e2580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=6899ea2dd30a3ed1
dashboard link: https://syzkaller.appspot.com/bug?extid=9db318d6167044609878
compiler:       Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
patch:          https://syzkaller.appspot.com/x/patch.diff?x=13088092580000

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