The patch titled Subject: hugetlb: fix null-ptr-deref in hugetlb_vma_lock_write has been added to the -mm mm-hotfixes-unstable branch. Its filename is hugetlb-fix-null-ptr-deref-in-hugetlb_vma_lock_write.patch

This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...

This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------ From: Mike Kravetz mike.kravetz@oracle.com Subject: hugetlb: fix null-ptr-deref in hugetlb_vma_lock_write Date: Mon, 13 Nov 2023 17:20:33 -0800

The routine __vma_private_lock tests for the existence of a reserve map associated with a private hugetlb mapping. A pointer to the reserve map is in vma->vm_private_data. __vma_private_lock was checking the pointer for NULL. However, it is possible that the low bits of the pointer could be used as flags. In such instances, vm_private_data is not NULL and not a valid pointer. This results in the null-ptr-deref reported by syzbot:

general protection fault, probably for non-canonical address 0xdffffc000000001d: 0000 [#1] PREEMPT SMP KASAN KASAN: null-ptr-deref in range [0x00000000000000e8-0x00000000000000ef] CPU: 0 PID: 5048 Comm: syz-executor139 Not tainted 6.6.0-rc7-syzkaller-00142-g88 8cf78c29e2 #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 1 0/09/2023 RIP: 0010:__lock_acquire+0x109/0x5de0 kernel/locking/lockdep.c:5004 ... Call Trace: <TASK> lock_acquire kernel/locking/lockdep.c:5753 [inline] lock_acquire+0x1ae/0x510 kernel/locking/lockdep.c:5718 down_write+0x93/0x200 kernel/locking/rwsem.c:1573 hugetlb_vma_lock_write mm/hugetlb.c:300 [inline] hugetlb_vma_lock_write+0xae/0x100 mm/hugetlb.c:291 __hugetlb_zap_begin+0x1e9/0x2b0 mm/hugetlb.c:5447 hugetlb_zap_begin include/linux/hugetlb.h:258 [inline] unmap_vmas+0x2f4/0x470 mm/memory.c:1733 exit_mmap+0x1ad/0xa60 mm/mmap.c:3230 __mmput+0x12a/0x4d0 kernel/fork.c:1349 mmput+0x62/0x70 kernel/fork.c:1371 exit_mm kernel/exit.c:567 [inline] do_exit+0x9ad/0x2a20 kernel/exit.c:861 __do_sys_exit kernel/exit.c:991 [inline] __se_sys_exit kernel/exit.c:989 [inline] __x64_sys_exit+0x42/0x50 kernel/exit.c:989 do_syscall_x64 arch/x86/entry/common.c:50 [inline] do_syscall_64+0x38/0xb0 arch/x86/entry/common.c:80 entry_SYSCALL_64_after_hwframe+0x63/0xcd

Mask off low bit flags before checking for NULL pointer. In addition, the reserve map only 'belongs' to the OWNER (parent in parent/child relationships) so also check for the OWNER flag.

Link: https://lkml.kernel.org/r/20231114012033.259600-1-mike.kravetz@oracle.com Reported-by: syzbot+6ada951e7c0f7bc8a71e@syzkaller.appspotmail.com Closes: https://lore.kernel.org/linux-mm/00000000000078d1e00608d7878b@google.com/ Fixes: bf4916922c60 ("hugetlbfs: extend hugetlb_vma_lock to private VMAs") Signed-off-by: Mike Kravetz mike.kravetz@oracle.com Reviewed-by: Rik van Riel riel@surriel.com Cc: Edward Adam Davis eadavis@qq.com Cc: Muchun Song muchun.song@linux.dev Cc: Nathan Chancellor nathan@kernel.org Cc: Nick Desaulniers ndesaulniers@google.com Cc: Tom Rix trix@redhat.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

include/linux/hugetlb.h | 5 +---- mm/hugetlb.c | 7 +++++++ 2 files changed, 8 insertions(+), 4 deletions(-)

--- a/include/linux/hugetlb.h~hugetlb-fix-null-ptr-deref-in-hugetlb_vma_lock_write +++ a/include/linux/hugetlb.h @@ -1268,10 +1268,7 @@ static inline bool __vma_shareable_lock( return (vma->vm_flags & VM_MAYSHARE) && vma->vm_private_data; }

-static inline bool __vma_private_lock(struct vm_area_struct *vma) -{ - return (!(vma->vm_flags & VM_MAYSHARE)) && vma->vm_private_data; -} +bool __vma_private_lock(struct vm_area_struct *vma);

/* * Safe version of huge_pte_offset() to check the locks. See comments --- a/mm/hugetlb.c~hugetlb-fix-null-ptr-deref-in-hugetlb_vma_lock_write +++ a/mm/hugetlb.c @@ -1182,6 +1182,13 @@ static int is_vma_resv_set(struct vm_are return (get_vma_private_data(vma) & flag) != 0; }

+bool __vma_private_lock(struct vm_area_struct *vma) +{ + return !(vma->vm_flags & VM_MAYSHARE) && + get_vma_private_data(vma) & ~HPAGE_RESV_MASK && + is_vma_resv_set(vma, HPAGE_RESV_OWNER); +} + void hugetlb_dup_vma_private(struct vm_area_struct *vma) { VM_BUG_ON_VMA(!is_vm_hugetlb_page(vma), vma); _

Patches currently in -mm which might be from mike.kravetz@oracle.com are

hugetlb-fix-null-ptr-deref-in-hugetlb_vma_lock_write.patch