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Message-ID: <6911dcc0.a70a0220.22f260.00ed.GAE@google.com> Date: Mon, 10 Nov 2025 04:38:24 -0800 From: syzbot <syzbot+e07658f51ca22ab65b4e@...kaller.appspotmail.com> To: brauner@...nel.org, jack@...e.cz, linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com, viro@...iv.linux.org.uk Subject: [syzbot] [fs?] KASAN: null-ptr-deref Read in drop_buffers (5) Hello, syzbot found the following issue on: HEAD commit: 7bb4d6512545 Merge tag 'v6.18rc4-SMB-client-fixes' of git:.. git tree: upstream console output: https://syzkaller.appspot.com/x/log.txt?x=17170412580000 kernel config: https://syzkaller.appspot.com/x/.config?x=b944b1e5afd39857 dashboard link: https://syzkaller.appspot.com/bug?extid=e07658f51ca22ab65b4e compiler: gcc (Debian 12.2.0-14+deb12u1) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40 Unfortunately, I don't have any reproducer for this issue yet. Downloadable assets: disk image: https://storage.googleapis.com/syzbot-assets/f75c0b0bb6c3/disk-7bb4d651.raw.xz vmlinux: https://storage.googleapis.com/syzbot-assets/f7a1ee597ee0/vmlinux-7bb4d651.xz kernel image: https://storage.googleapis.com/syzbot-assets/bd9a86dba20d/bzImage-7bb4d651.xz IMPORTANT: if you fix the issue, please add the following tag to the commit: Reported-by: syzbot+e07658f51ca22ab65b4e@...kaller.appspotmail.com ================================================================== BUG: KASAN: null-ptr-deref in instrument_atomic_read include/linux/instrumented.h:68 [inline] BUG: KASAN: null-ptr-deref in atomic_read include/linux/atomic/atomic-instrumented.h:32 [inline] BUG: KASAN: null-ptr-deref in buffer_busy fs/buffer.c:2886 [inline] BUG: KASAN: null-ptr-deref in drop_buffers.constprop.0+0x89/0x340 fs/buffer.c:2898 Read of size 4 at addr 0000000000000060 by task kswapd0/85 CPU: 0 UID: 0 PID: 85 Comm: kswapd0 Not tainted syzkaller #0 PREEMPT(full) Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025 Call Trace: <TASK> __dump_stack lib/dump_stack.c:94 [inline] dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:120 kasan_report+0xe0/0x110 mm/kasan/report.c:595 check_region_inline mm/kasan/generic.c:194 [inline] kasan_check_range+0x100/0x1b0 mm/kasan/generic.c:200 instrument_atomic_read include/linux/instrumented.h:68 [inline] atomic_read include/linux/atomic/atomic-instrumented.h:32 [inline] buffer_busy fs/buffer.c:2886 [inline] drop_buffers.constprop.0+0x89/0x340 fs/buffer.c:2898 try_to_free_buffers+0x21c/0x2d0 fs/buffer.c:2952 filemap_release_folio+0x219/0x280 mm/filemap.c:4423 shrink_folio_list+0x28a5/0x4800 mm/vmscan.c:1519 evict_folios+0x79c/0x1b30 mm/vmscan.c:4745 try_to_shrink_lruvec+0x585/0x9b0 mm/vmscan.c:4908 shrink_one+0x3e3/0x7a0 mm/vmscan.c:4953 shrink_many mm/vmscan.c:5016 [inline] lru_gen_shrink_node mm/vmscan.c:5094 [inline] shrink_node+0x26cb/0x3d80 mm/vmscan.c:6081 kswapd_shrink_node mm/vmscan.c:6941 [inline] balance_pgdat+0xbb8/0x1a50 mm/vmscan.c:7124 kswapd+0x590/0xb90 mm/vmscan.c:7389 kthread+0x3c5/0x780 kernel/kthread.c:463 ret_from_fork+0x675/0x7d0 arch/x86/kernel/process.c:158 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245 </TASK> ================================================================== Oops: general protection fault, probably for non-canonical address 0xdffffc000000000c: 0000 [#1] SMP KASAN NOPTI KASAN: null-ptr-deref in range [0x0000000000000060-0x0000000000000067] CPU: 0 UID: 0 PID: 85 Comm: kswapd0 Tainted: G B syzkaller #0 PREEMPT(full) Tainted: [B]=BAD_PAGE Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025 RIP: 0010:arch_atomic_read arch/x86/include/asm/atomic.h:23 [inline] RIP: 0010:raw_atomic_read include/linux/atomic/atomic-arch-fallback.h:457 [inline] RIP: 0010:atomic_read include/linux/atomic/atomic-instrumented.h:33 [inline] RIP: 0010:buffer_busy fs/buffer.c:2886 [inline] RIP: 0010:drop_buffers.constprop.0+0x90/0x340 fs/buffer.c:2898 Code: 4d 8b 76 08 4c 39 f3 0f 84 84 00 00 00 e8 f8 28 72 ff 4d 8d 66 60 be 04 00 00 00 4c 89 e7 e8 d7 cc d9 ff 4c 89 e0 48 c1 e8 03 <0f> b6 0c 28 4c 89 e0 83 e0 07 83 c0 03 38 c8 7c 08 84 c9 0f 85 2d RSP: 0018:ffffc9000239f0b0 EFLAGS: 00010216 RAX: 000000000000000c RBX: ffff888057ccd3e0 RCX: ffffffff817b40ef RDX: ffff88801ef18000 RSI: ffffffff82246d87 RDI: 0000000000000007 RBP: dffffc0000000000 R08: 0000000000000007 R09: 0000000000000000 R10: 0000000000000000 R11: 3d3d3d3d3d3d3d3d R12: 0000000000000060 R13: ffffea0000a77880 R14: 0000000000000000 R15: ffffea0000a778a8 FS: 0000000000000000(0000) GS:ffff888124a07000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 000055e34233c168 CR3: 0000000030ecb000 CR4: 0000000000350ef0 Call Trace: <TASK> try_to_free_buffers+0x21c/0x2d0 fs/buffer.c:2952 filemap_release_folio+0x219/0x280 mm/filemap.c:4423 shrink_folio_list+0x28a5/0x4800 mm/vmscan.c:1519 evict_folios+0x79c/0x1b30 mm/vmscan.c:4745 try_to_shrink_lruvec+0x585/0x9b0 mm/vmscan.c:4908 shrink_one+0x3e3/0x7a0 mm/vmscan.c:4953 shrink_many mm/vmscan.c:5016 [inline] lru_gen_shrink_node mm/vmscan.c:5094 [inline] shrink_node+0x26cb/0x3d80 mm/vmscan.c:6081 kswapd_shrink_node mm/vmscan.c:6941 [inline] balance_pgdat+0xbb8/0x1a50 mm/vmscan.c:7124 kswapd+0x590/0xb90 mm/vmscan.c:7389 kthread+0x3c5/0x780 kernel/kthread.c:463 ret_from_fork+0x675/0x7d0 arch/x86/kernel/process.c:158 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245 </TASK> Modules linked in: ---[ end trace 0000000000000000 ]--- RIP: 0010:arch_atomic_read arch/x86/include/asm/atomic.h:23 [inline] RIP: 0010:raw_atomic_read include/linux/atomic/atomic-arch-fallback.h:457 [inline] RIP: 0010:atomic_read include/linux/atomic/atomic-instrumented.h:33 [inline] RIP: 0010:buffer_busy fs/buffer.c:2886 [inline] RIP: 0010:drop_buffers.constprop.0+0x90/0x340 fs/buffer.c:2898 Code: 4d 8b 76 08 4c 39 f3 0f 84 84 00 00 00 e8 f8 28 72 ff 4d 8d 66 60 be 04 00 00 00 4c 89 e7 e8 d7 cc d9 ff 4c 89 e0 48 c1 e8 03 <0f> b6 0c 28 4c 89 e0 83 e0 07 83 c0 03 38 c8 7c 08 84 c9 0f 85 2d RSP: 0018:ffffc9000239f0b0 EFLAGS: 00010216 RAX: 000000000000000c RBX: ffff888057ccd3e0 RCX: ffffffff817b40ef RDX: ffff88801ef18000 RSI: ffffffff82246d87 RDI: 0000000000000007 RBP: dffffc0000000000 R08: 0000000000000007 R09: 0000000000000000 R10: 0000000000000000 R11: 3d3d3d3d3d3d3d3d R12: 0000000000000060 R13: ffffea0000a77880 R14: 0000000000000000 R15: ffffea0000a778a8 FS: 0000000000000000(0000) GS:ffff888124a07000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 000055e34233c168 CR3: 0000000030ecb000 CR4: 0000000000350ef0 ---------------- Code disassembly (best guess): 0: 4d 8b 76 08 mov 0x8(%r14),%r14 4: 4c 39 f3 cmp %r14,%rbx 7: 0f 84 84 00 00 00 je 0x91 d: e8 f8 28 72 ff call 0xff72290a 12: 4d 8d 66 60 lea 0x60(%r14),%r12 16: be 04 00 00 00 mov $0x4,%esi 1b: 4c 89 e7 mov %r12,%rdi 1e: e8 d7 cc d9 ff call 0xffd9ccfa 23: 4c 89 e0 mov %r12,%rax 26: 48 c1 e8 03 shr $0x3,%rax * 2a: 0f b6 0c 28 movzbl (%rax,%rbp,1),%ecx <-- trapping instruction 2e: 4c 89 e0 mov %r12,%rax 31: 83 e0 07 and $0x7,%eax 34: 83 c0 03 add $0x3,%eax 37: 38 c8 cmp %cl,%al 39: 7c 08 jl 0x43 3b: 84 c9 test %cl,%cl 3d: 0f .byte 0xf 3e: 85 .byte 0x85 3f: 2d .byte 0x2d --- 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 report is already addressed, let syzbot know by replying with: #syz fix: exact-commit-title If you want to overwrite report's subsystems, reply with: #syz set subsystems: new-subsystem (See the list of subsystem names on the web dashboard) If the report is a duplicate of another one, reply with: #syz dup: exact-subject-of-another-report If you want to undo deduplication, reply with: #syz undup
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