The syzbot reported the below general protection fault: general protection fault, probably for non-canonical address 0xe00eeaee0000003b: 0000 [#1] PREEMPT SMP KASAN KASAN: maybe wild-memory-access in range [0x00777770000001d8-0x00777770000001df] CPU: 1 PID: 10488 Comm: syz-executor721 Not tainted 5.9.0-rc3-syzkaller #0 RIP: 0010:unlink_file_vma+0x57/0xb0 mm/mmap.c:164 Call Trace: free_pgtables+0x1b3/0x2f0 mm/memory.c:415 exit_mmap+0x2c0/0x530 mm/mmap.c:3184 __mmput+0x122/0x470 kernel/fork.c:1076 mmput+0x53/0x60 kernel/fork.c:1097 exit_mm kernel/exit.c:483 [inline] do_exit+0xa8b/0x29f0 kernel/exit.c:793 do_group_exit+0x125/0x310 kernel/exit.c:903 get_signal+0x428/0x1f00 kernel/signal.c:2757 arch_do_signal+0x82/0x2520 arch/x86/kernel/signal.c:811 exit_to_user_mode_loop kernel/entry/common.c:136 [inline] exit_to_user_mode_prepare+0x1ae/0x200 kernel/entry/common.c:167 syscall_exit_to_user_mode+0x7e/0x2e0 kernel/entry/common.c:242 entry_SYSCALL_64_after_hwframe+0x44/0xa9 It's because the ->mmap() callback can change vma->vm_file and fput the original file. But the commit d70cec898324 ("mm: mmap: merge vma after call_mmap() if possible") failed to catch this case and always fput() the original file, hence add an extra fput(). [ Thanks Hillf for pointing this extra fput() out. ]
Unified · Split
| @@ -1781,7 +1781,11 @@ unsigned long mmap_region(struct file *file, unsigned long addr, · 1780 unmodified lines | |||
| 1781 | merge = vma_merge(mm, prev, vma->vm_start, vma->vm_end, vma->vm_flags, | 1781 | merge = vma_merge(mm, prev, vma->vm_start, vma->vm_end, vma->vm_flags, |
| 1782 | NULL, vma->vm_file, vma->vm_pgoff, NULL, NULL_VM_UFFD_CTX); | 1782 | NULL, vma->vm_file, vma->vm_pgoff, NULL, NULL_VM_UFFD_CTX); |
| 1783 | if (merge) { | 1783 | if (merge) { |
| 1784 | fput(file); | 1784 | /* ->mmap() can change vma->vm_file and fput the original file. So |
| 1785 | * fput the vma->vm_file here or we would add an extra fput for file | ||
| 1786 | * and cause general protection fault ultimately. | ||
| 1787 | */ | ||
| 1788 | fput(vma->vm_file); | ||
| 1785 | vm_area_free(vma); | 1789 | vm_area_free(vma); |
| 1786 | vma = merge; | 1790 | vma = merge; |
| 1787 | /* Update vm_flags and possible addr to pick up the change. We don't | 1791 | /* Update vm_flags and possible addr to pick up the change. We don't |