From: Manas <manas18244@xxxxxxxxxxx> syzbot has pointed to a possible null pointer dereference in pfnmap_lockdep_assert. vm_file member of vm_area_struct is being dereferenced without any checks. This fix assigns mapping only if vm_file is not NULL. Reported-by: syzbot+093d096417e7038a689b@xxxxxxxxxxxxxxxxxxxxxxxxx Closes: https://syzkaller.appspot.com/bug?extid=093d096417e7038a689b --- This bug[1] triggers a general protection fault in follow_pfnmap_start function. An assertion pfnmap_lockdep_assert inside this function dereferences vm_file member of vm_area_struct. And panic gets triggered when vm_file is NULL. This patch assigns mapping only if vm_file is not NULL. [1] https://syzkaller.appspot.com/bug?extid=093d096417e7038a689b Signed-off-by: Manas <manas18244@xxxxxxxxxxx> --- Changes in v4: - v4: simplify ternary conditional - Link to v3: https://lore.kernel.org/r/20241004-fix-null-deref-v3-1-f9459b1cc95f@xxxxxxxxxxx Changes in v3: - v3: use assigned var instead of accessing member again - Link to v2: https://lore.kernel.org/r/20241004-fix-null-deref-v2-1-23ad90999cd1@xxxxxxxxxxx Changes in v2: - v2: use ternary operator according to feedback - Link to v1: https://lore.kernel.org/r/20241003-fix-null-deref-v1-1-0a45df9d016a@xxxxxxxxxxx --- mm/memory.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/mm/memory.c b/mm/memory.c index 2366578015ad..4e4d598496a8 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -6346,10 +6346,13 @@ static inline void pfnmap_args_setup(struct follow_pfnmap_args *args, static inline void pfnmap_lockdep_assert(struct vm_area_struct *vma) { #ifdef CONFIG_LOCKDEP - struct address_space *mapping = vma->vm_file->f_mapping; + struct address_space *mapping = NULL; + + if (vma->vm_file) + mapping = vma->vm_file->f_mapping; if (mapping) - lockdep_assert(lockdep_is_held(&vma->vm_file->f_mapping->i_mmap_rwsem) || + lockdep_assert(lockdep_is_held(&mapping->i_mmap_rwsem) || lockdep_is_held(&vma->vm_mm->mmap_lock)); else lockdep_assert(lockdep_is_held(&vma->vm_mm->mmap_lock)); --- base-commit: 9852d85ec9d492ebef56dc5f229416c925758edc change-id: 20241003-fix-null-deref-6bfa0337efc3 Best regards, -- Manas <manas18244@xxxxxxxxxxx>
