vma_is_anonymous() relies on ->vm_ops being NULL to detect anonymous VMA. This is unreliable as ->mmap may not set ->vm_ops.

False-positive vma_is_anonymous() may lead to crashes:

next ffff8801ce5e7040 prev ffff8801d20eca50 mm ffff88019c1e13c0 prot 27 anon_vma ffff88019680cdd8 vm_ops 0000000000000000 pgoff 0 file ffff8801b2ec2d00 private_data 0000000000000000 flags: 0xff(read|write|exec|shared|mayread|maywrite|mayexec|mayshare) ------------[ cut here ]------------ kernel BUG at mm/memory.c:1422! invalid opcode: 0000 [#1] SMP KASAN CPU: 0 PID: 18486 Comm: syz-executor3 Not tainted 4.18.0-rc3+ #136 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 RIP: 0010:zap_pmd_range mm/memory.c:1421 [inline] RIP: 0010:zap_pud_range mm/memory.c:1466 [inline] RIP: 0010:zap_p4d_range mm/memory.c:1487 [inline] RIP: 0010:unmap_page_range+0x1c18/0x2220 mm/memory.c:1508 Code: ff 31 ff 4c 89 e6 42 c6 04 33 f8 e8 92 dd d0 ff 4d 85 e4 0f 85 4a eb ff ff e8 54 dc d0 ff 48 8b bd 10 fc ff ff e8 82 95 fe ff <0f> 0b e8 41 dc d0 ff 0f 0b 4c 89 ad 18 fc ff ff c7 85 7c fb ff ff RSP: 0018:ffff8801b0587330 EFLAGS: 00010286 RAX: 000000000000013c RBX: 1ffff100360b0e9c RCX: ffffc90002620000 RDX: 0000000000000000 RSI: ffffffff81631851 RDI: 0000000000000001 RBP: ffff8801b05877c8 R08: ffff880199d40300 R09: ffffed003b5c4fc0 R10: ffffed003b5c4fc0 R11: ffff8801dae27e07 R12: 0000000000000000 R13: ffff88019c1e13c0 R14: dffffc0000000000 R15: 0000000020e01000 FS: 00007fca32251700(0000) GS:ffff8801dae00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007f04c540d000 CR3: 00000001ac1f0000 CR4: 00000000001426f0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Call Trace: unmap_single_vma+0x1a0/0x310 mm/memory.c:1553 zap_page_range_single+0x3cc/0x580 mm/memory.c:1644 unmap_mapping_range_vma mm/memory.c:2792 [inline] unmap_mapping_range_tree mm/memory.c:2813 [inline] unmap_mapping_pages+0x3a7/0x5b0 mm/memory.c:2845 unmap_mapping_range+0x48/0x60 mm/memory.c:2880 truncate_pagecache+0x54/0x90 mm/truncate.c:800 truncate_setsize+0x70/0xb0 mm/truncate.c:826 simple_setattr+0xe9/0x110 fs/libfs.c:409 notify_change+0xf13/0x10f0 fs/attr.c:335 do_truncate+0x1ac/0x2b0 fs/open.c:63 do_sys_ftruncate+0x492/0x560 fs/open.c:205 __do_sys_ftruncate fs/open.c:215 [inline] __se_sys_ftruncate fs/open.c:213 [inline] __x64_sys_ftruncate+0x59/0x80 fs/open.c:213 do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290 entry_SYSCALL_64_after_hwframe+0x49/0xbe

Reproducer:

#include <stdio.h> #include <stddef.h> #include <stdint.h> #include <stdlib.h> #include <string.h> #include <sys/types.h> #include <sys/stat.h> #include <sys/ioctl.h> #include <sys/mman.h> #include <unistd.h> #include <fcntl.h>

#define KCOV_INIT_TRACE _IOR('c', 1, unsigned long) #define KCOV_ENABLE _IO('c', 100) #define KCOV_DISABLE _IO('c', 101) #define COVER_SIZE (1024<<10)

#define KCOV_TRACE_PC 0 #define KCOV_TRACE_CMP 1

int main(int argc, char **argv) { int fd; unsigned long *cover;

system("mount -t debugfs none /sys/kernel/debug"); fd = open("/sys/kernel/debug/kcov", O_RDWR); ioctl(fd, KCOV_INIT_TRACE, COVER_SIZE); cover = mmap(NULL, COVER_SIZE * sizeof(unsigned long), PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0); munmap(cover, COVER_SIZE * sizeof(unsigned long)); cover = mmap(NULL, COVER_SIZE * sizeof(unsigned long), PROT_READ | PROT_WRITE, MAP_PRIVATE, fd, 0); memset(cover, 0, COVER_SIZE * sizeof(unsigned long)); ftruncate(fd, 3UL << 20); return 0; }

This can be fixed by assigning anonymous VMAs own vm_ops and not relying on it being NULL.

If ->mmap() failed to set ->vm_ops, mmap_region() will set it to dummy_vm_ops. This way we will have non-NULL ->vm_ops for all VMAs.

Signed-off-by: Kirill A. Shutemov kirill.shutemov@linux.intel.com Reported-by: syzbot+3f84280d52be9b7083cc@syzkaller.appspotmail.com Cc: stable@vger.kernel.org Cc: Dmitry Vyukov dvyukov@google.com Cc: Oleg Nesterov oleg@redhat.com Cc: Andrea Arcangeli aarcange@redhat.com --- drivers/char/mem.c | 1 + fs/exec.c | 1 + fs/hugetlbfs/inode.c | 1 + include/linux/mm.h | 5 ++++- mm/khugepaged.c | 4 ++-- mm/mmap.c | 13 +++++++++++++ mm/shmem.c | 1 + 7 files changed, 23 insertions(+), 3 deletions(-)

diff --git a/drivers/char/mem.c b/drivers/char/mem.c index ffeb60d3434c..f0a8b0b1768b 100644 --- a/drivers/char/mem.c +++ b/drivers/char/mem.c @@ -708,6 +708,7 @@ static int mmap_zero(struct file *file, struct vm_area_struct *vma) #endif if (vma->vm_flags & VM_SHARED) return shmem_zero_setup(vma); + vma->vm_ops = &anon_vm_ops; return 0; }

diff --git a/fs/exec.c b/fs/exec.c index 2d4e0075bd24..a1a246062561 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -307,6 +307,7 @@ static int __bprm_mm_init(struct linux_binprm *bprm) * configured yet. */ BUILD_BUG_ON(VM_STACK_FLAGS & VM_STACK_INCOMPLETE_SETUP); + vma->vm_ops = &anon_vm_ops; vma->vm_end = STACK_TOP_MAX; vma->vm_start = vma->vm_end - PAGE_SIZE; vma->vm_flags = VM_SOFTDIRTY | VM_STACK_FLAGS | VM_STACK_INCOMPLETE_SETUP; diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c index d508c7844681..5ff73b1398ad 100644 --- a/fs/hugetlbfs/inode.c +++ b/fs/hugetlbfs/inode.c @@ -597,6 +597,7 @@ static long hugetlbfs_fallocate(struct file *file, int mode, loff_t offset, memset(&pseudo_vma, 0, sizeof(struct vm_area_struct)); pseudo_vma.vm_flags = (VM_HUGETLB | VM_MAYSHARE | VM_SHARED); pseudo_vma.vm_file = file; + pseudo_vma.vm_ops = &dummy_vm_ops;

for (index = start; index < end; index++) { /* diff --git a/include/linux/mm.h b/include/linux/mm.h index a0fbb9ffe380..9a35362bbc92 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -1536,9 +1536,12 @@ int clear_page_dirty_for_io(struct page *page);

int get_cmdline(struct task_struct *task, char *buffer, int buflen);

+extern const struct vm_operations_struct anon_vm_ops; +extern const struct vm_operations_struct dummy_vm_ops; + static inline bool vma_is_anonymous(struct vm_area_struct *vma) { - return !vma->vm_ops; + return vma->vm_ops == &anon_vm_ops; }

#ifdef CONFIG_SHMEM diff --git a/mm/khugepaged.c b/mm/khugepaged.c index d7b2a4bf8671..5ae34097aed1 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -440,7 +440,7 @@ int khugepaged_enter_vma_merge(struct vm_area_struct *vma, * page fault if needed. */ return 0; - if (vma->vm_ops || (vm_flags & VM_NO_KHUGEPAGED)) + if (!vma_is_anonymous(vma) || (vm_flags & VM_NO_KHUGEPAGED)) /* khugepaged not yet working on file or special mappings */ return 0; hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK; @@ -831,7 +831,7 @@ static bool hugepage_vma_check(struct vm_area_struct *vma) return IS_ALIGNED((vma->vm_start >> PAGE_SHIFT) - vma->vm_pgoff, HPAGE_PMD_NR); } - if (!vma->anon_vma || vma->vm_ops) + if (!vma->anon_vma || !vma_is_anonymous(vma)) return false; if (is_vma_temporary_stack(vma)) return false; diff --git a/mm/mmap.c b/mm/mmap.c index d1eb87ef4b1a..0729ed06b01c 100644 --- a/mm/mmap.c +++ b/mm/mmap.c @@ -71,6 +71,9 @@ int mmap_rnd_compat_bits __read_mostly = CONFIG_ARCH_MMAP_RND_COMPAT_BITS; static bool ignore_rlimit_data; core_param(ignore_rlimit_data, ignore_rlimit_data, bool, 0644);

+const struct vm_operations_struct anon_vm_ops = {}; +const struct vm_operations_struct dummy_vm_ops = {}; + static void unmap_region(struct mm_struct *mm, struct vm_area_struct *vma, struct vm_area_struct *prev, unsigned long start, unsigned long end); @@ -561,6 +564,8 @@ static unsigned long count_vma_pages_range(struct mm_struct *mm, void __vma_link_rb(struct mm_struct *mm, struct vm_area_struct *vma, struct rb_node **rb_link, struct rb_node *rb_parent) { + WARN_ONCE(!vma->vm_ops, "missing vma->vm_ops"); + /* Update tracking information for the gap following the new vma. */ if (vma->vm_next) vma_gap_update(vma->vm_next); @@ -1774,12 +1779,19 @@ unsigned long mmap_region(struct file *file, unsigned long addr, */ WARN_ON_ONCE(addr != vma->vm_start);

+ /* All mappings must have ->vm_ops set */ + if (!vma->vm_ops) + vma->vm_ops = &dummy_vm_ops; + addr = vma->vm_start; vm_flags = vma->vm_flags; } else if (vm_flags & VM_SHARED) { error = shmem_zero_setup(vma); if (error) goto free_vma; + } else { + /* vma_is_anonymous() relies on this. */ + vma->vm_ops = &anon_vm_ops; }

vma_link(mm, vma, prev, rb_link, rb_parent); @@ -2999,6 +3011,7 @@ static int do_brk_flags(unsigned long addr, unsigned long request, unsigned long

INIT_LIST_HEAD(&vma->anon_vma_chain); vma->vm_mm = mm; + vma->vm_ops = &anon_vm_ops; vma->vm_start = addr; vma->vm_end = addr + len; vma->vm_pgoff = pgoff; diff --git a/mm/shmem.c b/mm/shmem.c index 2cab84403055..db5c319161ca 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -1424,6 +1424,7 @@ static void shmem_pseudo_vma_init(struct vm_area_struct *vma, /* Bias interleave by inode number to distribute better across nodes */ vma->vm_pgoff = index + info->vfs_inode.i_ino; vma->vm_policy = mpol_shared_policy_lookup(&info->policy, index); + vma->vm_ops = &dummy_vm_ops; }

static void shmem_pseudo_vma_destroy(struct vm_area_struct *vma)