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ntfs: fix kunmap_local() of advanced pointers in check_mft_mirror()

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check_mft_mirror() compares the mft records of a page with the mirror
records by advancing kmft and kmirr by the record size for every record.
It then passes the advanced pointers to kunmap_local(). After the last
record of a page they point one page past the mapping.

With HIGHMEM kunmap_local() warns that the address does not match the
top of the kmap_local stack. What it does next depends on how the
architecture finds the page table entry:

- 32-bit ARM looks the entry up by that address. It clears the entry of
  the neighbouring fixmap slot and leaves the real mapping in place.
  The next kmap_local() on that CPU that reaches the slot hits the
  BUG_ON(!pte_none()) in __kmap_local_pfn_prot().
- x86-32 takes the entry from the stack index, so the wrong address
  does not select a wrong entry. In QEMU the mount carried on after the
  warning.

With 4 KiB pages and 1 KiB mft records the four mirror records fill
exactly one page, so every mount whose $MFT and $MFTMirr folios are in
highmem hits it. A fresh mkntfs volume on 32-bit ARM
(multi_v7_defconfig, 256 MiB of highmem) fails on the first mount:

  WARNING: mm/highmem.c:623 at kunmap_local_indexed+0x254/0x26c, CPU#1: mount/85
   kunmap_local_indexed from ntfs_fill_super+0x224c/0x35a0
   ntfs_fill_super from get_tree_bdev_flags+0x1d8/0x2a4
  ntfs: volume version 3.1, dev loop0, cluster size 4096
  kernel BUG at mm/highmem.c:565!
  PC is at __kmap_local_pfn_prot+0x210/0x214
   __kmap_local_page_prot from ntfs_check_logfile+0x1fc/0x1210

Found with syzkaller. Kernels without HIGHMEM do not show it.
kmap_local_folio() returns the direct map address there and
kunmap_local() has no mapping to remove.

Keep the addresses returned by kmap_local_folio() and unmap with those.

Fixes: 6251f0b0de ("ntfs: update super block operations")
Cc: stable@vger.kernel.org
Assisted-by: LLM
Signed-off-by: Karl Mehltretter <kmehltretter@gmail.com>
Reviewed-by: Hyunchul Lee <hyc.lee@gmail.com>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
This commit is contained in:
Karl Mehltretter 2026-10-06 06:51:35 +02:00 committed by Namjae Jeon
parent c10e0c3769
commit 16fcb1c446
1 changed files with 11 additions and 9 deletions
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20
fs/ntfs/super.c
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@ -1132,7 +1132,7 @@ static bool check_mft_mirror(struct ntfs_volume *vol)
struct super_block *sb = vol->sb;
struct ntfs_inode *mirr_ni;
struct folio *mft_folio = NULL, *mirr_folio = NULL;
u8 *kmft = NULL, *kmirr = NULL;
u8 *kmft = NULL, *kmirr = NULL, *kmft_base = NULL, *kmirr_base = NULL;
struct runlist_element *rl, rl2[2];
pgoff_t index;
int mrecs_per_page, i;
@ -1147,9 +1147,9 @@ static bool check_mft_mirror(struct ntfs_volume *vol)
/* Switch pages if necessary. */
if (!(i % mrecs_per_page)) {
if (index) {
kunmap_local(kmirr);
kunmap_local(kmirr_base);
folio_put(mirr_folio);
kunmap_local(kmft);
kunmap_local(kmft_base);
folio_put(mft_folio);
}
/* Get the $MFT page. */
@ -1159,7 +1159,8 @@ static bool check_mft_mirror(struct ntfs_volume *vol)
ntfs_error(sb, "Failed to read $MFT.");
return false;
}
kmft = kmap_local_folio(mft_folio, 0);
kmft_base = kmap_local_folio(mft_folio, 0);
kmft = kmft_base;
/* Get the $MFTMirr page. */
mirr_folio = read_mapping_folio(vol->mftmirr_ino->i_mapping,
index, NULL);
@ -1167,7 +1168,8 @@ static bool check_mft_mirror(struct ntfs_volume *vol)
ntfs_error(sb, "Failed to read $MFTMirr.");
goto mft_unmap_out;
}
kmirr = kmap_local_folio(mirr_folio, 0);
kmirr_base = kmap_local_folio(mirr_folio, 0);
kmirr = kmirr_base;
++index;
}
@ -1179,10 +1181,10 @@ static bool check_mft_mirror(struct ntfs_volume *vol)
"Incomplete multi sector transfer detected in mft record %i.",
i);
mm_unmap_out:
kunmap_local(kmirr);
kunmap_local(kmirr_base);
folio_put(mirr_folio);
mft_unmap_out:
kunmap_local(kmft);
kunmap_local(kmft_base);
folio_put(mft_folio);
return false;
}
@ -1218,9 +1220,9 @@ static bool check_mft_mirror(struct ntfs_volume *vol)
kmirr += vol->mft_record_size;
} while (++i < vol->mftmirr_size);
/* Release the last folios. */
kunmap_local(kmirr);
kunmap_local(kmirr_base);
folio_put(mirr_folio);
kunmap_local(kmft);
kunmap_local(kmft_base);
folio_put(mft_folio);
/* Construct the mft mirror runlist by hand. */