Hi, We found a bug in Linux 6.10 using syzkaller. It is possibly a null pointer dereference bug. The reprodcuer is https://gist.github.com/freexxxyyy/315733cb1dc3bc8cbe055b457c1918c0 The bug report is: Syzkaller hit 'general protection fault in get_mem_cgroup_from_objcg' bug. Oops: general protection fault, probably for non-canonical address 0xdffffc000000000a: 0000 [#1] PREEMPT SMP KASAN PTI KASAN: null-ptr-deref in range [0x0000000000000050-0x0000000000000057] CPU: 0 PID: 8129 Comm: syz-executor347 Not tainted 6.10.0 #13 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014 RIP: 0010:css_tryget include/linux/cgroup_refcnt.h:44 [inline] RIP: 0010:get_mem_cgroup_from_objcg+0xb1/0x150 include/linux/memcontrol.h:536 Code: 49 83 c4 10 4c 89 e5 48 c1 ed 03 42 80 7c 2d 00 00 74 08 4c 89 e7 e8 3e 3e f8 ff 4d 8b 3c 24 49 8d 5f 54 48 89 d8 48 c1 e8 03 <42> 0f b6 04 28 84 c0 75 14 f6 03 01 75 25 49 8d 7f 10 e8 a8 ac 00 RSP: 0018:ffffc9000abb74e8 EFLAGS: 00010207 RAX: 000000000000000a RBX: 0000000000000054 RCX: ffff888014bd5a00 RDX: 0000000000000000 RSI: ffffffff8ba956c0 RDI: ffffffff8ba95680 RBP: 1ffff110057e4c72 R08: dffffc0000000000 R09: 1ffffffff221f8b0 R10: dffffc0000000000 R11: fffffbfff221f8b1 R12: ffff88802bf26390 R13: dffffc0000000000 R14: ffffffff81fc1db9 R15: 0000000000000000 FS: 0000000000000000(0000) GS:ffff888063a00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007f5504f14000 CR3: 000000001e6f2000 CR4: 0000000000350ef0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Call Trace: <TASK> obj_cgroup_uncharge_pages mm/memcontrol.c:3392 [inline] refill_obj_stock+0x41e/0x6b0 mm/memcontrol.c:3665 obj_cgroup_uncharge mm/memcontrol.c:3714 [inline] __memcg_slab_free_hook+0x1db/0x310 mm/memcontrol.c:3801 memcg_slab_free_hook mm/slub.c:2130 [inline] slab_free mm/slub.c:4435 [inline] kmem_cache_free+0x194/0x280 mm/slub.c:4513 anon_vma_chain_free mm/rmap.c:147 [inline] unlink_anon_vmas+0x58b/0x5e0 mm/rmap.c:447 free_pgtables+0x215/0xbb0 mm/memory.c:386 exit_mmap+0x435/0xa20 mm/mmap.c:3352 __mmput+0x114/0x3b0 kernel/fork.c:1346 exit_mm+0x207/0x2e0 kernel/exit.c:567 do_exit+0x996/0x2560 kernel/exit.c:863 do_group_exit+0x1fd/0x2b0 kernel/exit.c:1025 get_signal+0x1697/0x1730 kernel/signal.c:2909 arch_do_signal_or_restart+0x92/0x7f0 arch/x86/kernel/signal.c:310 exit_to_user_mode_loop kernel/entry/common.c:111 [inline] exit_to_user_mode_prepare include/linux/entry-common.h:328 [inline] __syscall_exit_to_user_mode_work kernel/entry/common.c:207 [inline] syscall_exit_to_user_mode+0x95/0x280 kernel/entry/common.c:218 do_syscall_64+0x8a/0x150 arch/x86/entry/common.c:89 entry_SYSCALL_64_after_hwframe+0x67/0x6f RIP: 0033:0x7f3ec1159bed Code: Unable to access opcode bytes at 0x7f3ec1159bc3. RSP: 002b:00007fff23d68ba8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010 RAX: 0000000000000002 RBX: 0000000000000003 RCX: 00007f3ec1159bed RDX: 0000000020000080 RSI: 0000000000000001 RDI: 0000000000000003 RBP: 0000000000000000 R08: 002367732f766564 R09: 00007fff23d68c30 R10: 000000000000000f R11: 0000000000000246 R12: 0000000000000001 R13: 00007fff23d68bf0 R14: 0000000000000000 R15: 00007fff23d68c30 </TASK> Modules linked in: ---[ end trace 0000000000000000 ]--- RIP: 0010:css_tryget include/linux/cgroup_refcnt.h:44 [inline] RIP: 0010:get_mem_cgroup_from_objcg+0xb1/0x150 include/linux/memcontrol.h:536 Code: 49 83 c4 10 4c 89 e5 48 c1 ed 03 42 80 7c 2d 00 00 74 08 4c 89 e7 e8 3e 3e f8 ff 4d 8b 3c 24 49 8d 5f 54 48 89 d8 48 c1 e8 03 <42> 0f b6 04 28 84 c0 75 14 f6 03 01 75 25 49 8d 7f 10 e8 a8 ac 00 RSP: 0018:ffffc9000abb74e8 EFLAGS: 00010207 RAX: 000000000000000a RBX: 0000000000000054 RCX: ffff888014bd5a00 RDX: 0000000000000000 RSI: ffffffff8ba956c0 RDI: ffffffff8ba95680 RBP: 1ffff110057e4c72 R08: dffffc0000000000 R09: 1ffffffff221f8b0 R10: dffffc0000000000 R11: fffffbfff221f8b1 R12: ffff88802bf26390 R13: dffffc0000000000 R14: ffffffff81fc1db9 R15: 0000000000000000 FS: 0000000000000000(0000) GS:ffff888063a00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007f5504f14000 CR3: 000000001a258000 CR4: 0000000000350ef0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 ---------------- Code disassembly (best guess): 0: 49 83 c4 10 add $0x10,%r12 4: 4c 89 e5 mov %r12,%rbp 7: 48 c1 ed 03 shr $0x3,%rbp b: 42 80 7c 2d 00 00 cmpb $0x0,0x0(%rbp,%r13,1) 11: 74 08 je 0x1b 13: 4c 89 e7 mov %r12,%rdi 16: e8 3e 3e f8 ff call 0xfff83e59 1b: 4d 8b 3c 24 mov (%r12),%r15 1f: 49 8d 5f 54 lea 0x54(%r15),%rbx 23: 48 89 d8 mov %rbx,%rax 26: 48 c1 e8 03 shr $0x3,%rax * 2a: 42 0f b6 04 28 movzbl (%rax,%r13,1),%eax <-- trapping instruction 2f: 84 c0 test %al,%al 31: 75 14 jne 0x47 33: f6 03 01 testb $0x1,(%rbx) 36: 75 25 jne 0x5d 38: 49 8d 7f 10 lea 0x10(%r15),%rdi 3c: e8 .byte 0xe8 3d: a8 ac test $0xac,%al -- Yours sincerely, Xingyu
