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ntfs_init_fs_context() allocates a fresh ntfs_volume with vol->upcase
left as NULL. ntfs_free_fs_context() unconditionally calls
ntfs_volume_free() during fs_context teardown, even when ntfs_fill_super()
never ran or already cleaned up. ntfs_volume_free() then executes:
mutex_lock(&ntfs_lock);
if (vol->upcase == default_upcase) {
ntfs_nr_upcase_users--;
vol->upcase = NULL;
}
When the global default_upcase is also NULL (very first mount attempt,
or all prior mounts have released the table), the comparison is
NULL == NULL, and ntfs_nr_upcase_users is decremented even though this
volume never claimed a reference. ntfs_nr_upcase_users is unsigned long,
so the decrement wraps to ULONG_MAX.
A subsequent successful mount can then free the shared table while the
mounted volume still points at it:
1. ntfs_fill_super() does the temporary ntfs_nr_upcase_users++ at the
"Generate the global default upcase table if necessary" block. With
the prior wraparound this brings the counter back to 0.
2. If the volume's $UpCase matches the default, the match path does
ntfs_nr_upcase_users++ and sets vol->upcase = default_upcase. The
counter is now 1.
3. On the success path, !--ntfs_nr_upcase_users evaluates true and
default_upcase is kvfree()'d while vol->upcase still points at it.
Subsequent upcase comparisons through that mount touch freed
memory.
This was reproduced with KASAN by closing a fresh fsopen("ntfs") context,
then mounting an NTFS image whose $UpCase table matches
generate_default_upcase(), and finally doing a case-insensitive lookup.
KASAN reports the dangling vol->upcase access:
BUG: KASAN: use-after-free in ntfs_collate_names+0x3b4/0x420
Read of size 2 at addr ffff888008d40048 by task init/1
ntfs_collate_names+0x3b4/0x420
ntfs_lookup_inode_by_name+0x1921/0x3130
ntfs_lookup+0x193/0xc40
vfs_statx+0xc7/0x190
vfs_fstatat+0x4b/0xa0
__do_sys_newfstatat+0x92/0xf0
The same QEMU reproducer was rerun after this change with KASAN
enabled. It reached "reproducer finished", and the log contained no
KASAN, use-after-free, Oops, or panic signatures.
Guard each comparison with an explicit vol->upcase non-NULL check so a
volume that never took a reference cannot decrement the global users
counter. Apply the same guard to the other default_upcase release sites
so all cleanup paths follow the same ownership rule: only volumes that
actually hold a default_upcase reference may drop one.
Fixes:
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||
|---|---|---|
| arch | ||
| block | ||
| certs | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| io_uring | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| rust | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .clippy.toml | ||
| .cocciconfig | ||
| .editorconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| .pylintrc | ||
| .rustfmt.toml | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
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