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ntfs: fix kmap_local leak in ntfs_check_logfile()

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ntfs_check_logfile() calls kmap_local_folio() on every iteration of its
search loop but kunmap_local() only once per folio. The loop visits
positions 0, 512, 1024, 2048, 4096 and so on. With 4 KiB pages the first
four are in one page, so a mount whose first LogFile folio is in highmem
leaves three entries on the kmap_local stack of the mounting task.
Kernels without HIGHMEM are not affected.

The leaked entries keep migration disabled. nr_pinned of the runqueue
the mount ran on stays raised after the task exits, so taking that CPU
offline blocks forever in balance_hotplug_wait().

The fifth mount in one task reaches KM_MAX_IDX (12 leaked entries plus
4 in the loop) and hits the BUG_ON() in kmap_local_idx_push():

  kernel BUG at mm/highmem.c:480!

On x86-32 the generic entry code also warns on return to user space:

  DEBUG_LOCKS_WARN_ON(current->kmap_ctrl.idx)
  WARNING: include/linux/highmem-internal.h:17 at __do_fast_syscall_32+0x21e/0x550

Map each page once, when it is read, and unmap that address.

Fixes: 5218cd102a ("ntfs: update misc 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 06:51:36 +02:00 committed by Namjae Jeon
parent 16fcb1c446
commit a5ec710849
1 changed files with 6 additions and 5 deletions
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11
fs/ntfs/logfile.c
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@ -457,7 +457,7 @@ bool ntfs_check_logfile(struct inode *log_vi, struct restart_page_header **rp)
struct ntfs_volume *vol = NTFS_SB(log_vi->i_sb);
struct address_space *mapping = log_vi->i_mapping;
struct folio *folio = NULL;
u8 *kaddr = NULL;
u8 *kaddr = NULL, *kbase = NULL;
struct restart_page_header *rstr1_ph = NULL;
struct restart_page_header *rstr2_ph = NULL;
int log_page_size, err;
@ -511,7 +511,7 @@ bool ntfs_check_logfile(struct inode *log_vi, struct restart_page_header **rp)
if (!folio || folio->index != idx) {
if (folio) {
kunmap_local(kaddr);
kunmap_local(kbase);
folio_put(folio);
}
folio = read_mapping_folio(mapping, idx, NULL);
@ -520,8 +520,9 @@ bool ntfs_check_logfile(struct inode *log_vi, struct restart_page_header **rp)
idx);
goto err_out;
}
kbase = kmap_local_folio(folio, 0);
}
kaddr = (u8 *)kmap_local_folio(folio, 0) + (pos & ~PAGE_MASK);
kaddr = kbase + (pos & ~PAGE_MASK);
/*
* A non-empty block means the logfile is not empty while an
* empty block after a non-empty block has been encountered
@ -574,7 +575,7 @@ bool ntfs_check_logfile(struct inode *log_vi, struct restart_page_header **rp)
* find a valid one further in the file.
*/
if (err != -EINVAL) {
kunmap_local(kaddr);
kunmap_local(kbase);
folio_put(folio);
goto err_out;
}
@ -583,7 +584,7 @@ bool ntfs_check_logfile(struct inode *log_vi, struct restart_page_header **rp)
pos = NTFS_BLOCK_SIZE >> 1;
}
if (folio) {
kunmap_local(kaddr);
kunmap_local(kbase);
folio_put(folio);
}
if (logfile_is_empty) {