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fs/ntfs3: preserve non-DOS attribute bits in system.dos_attrib

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[BUG]
A corrupted ntfs3 image can hit a NULL function pointer call in
generic_perform_write() after toggling system.ntfs_attrib and then
overwriting system.dos_attrib on the same file.

BUG: kernel NULL pointer dereference, address: 0000000000000000
\#PF: supervisor instruction fetch in kernel mode
\#PF: error_code(0x0010) - not-present page
PGD bed5067 P4D bed5067 PUD 0
Oops: Oops: 0010 [#1] SMP KASAN NOPTI
RIP: 0010:0x0
Code: Unable to access opcode bytes at 0xffffffffffffffd6.
RSP: 0018:ffff88801025f988 EFLAGS: 00010246
Call Trace:
 generic_perform_write+0x409/0x8c0 mm/filemap.c:4255
 __generic_file_write_iter+0x1bb/0x200 mm/filemap.c:4372
 ntfs_file_write_iter+0xcd9/0x1c20 fs/ntfs3/file.c:1253
 new_sync_write fs/read_write.c:593 [inline]
 vfs_write+0x63b/0xf70 fs/read_write.c:686
 ksys_write+0x133/0x250 fs/read_write.c:738
 __do_sys_write fs/read_write.c:749 [inline]
 __se_sys_write fs/read_write.c:746 [inline]
 __x64_sys_write+0x77/0xc0 fs/read_write.c:746
 ...

[CAUSE]
system.ntfs_attrib updates ATTR_DATA flags via ni_new_attr_flags()
and switches i_mapping->a_ops to ntfs_aops_cmpr when
FILE_ATTRIBUTE_COMPRESSED is set. system.dos_attrib then overwrites
ni->std_fa from a one-byte DOS attribute value, clearing the compression
bit without updating ATTR_DATA or the mapping operations.

Old buffered writes use is_compressed(ni) to choose
__generic_file_write_iter(). That leaves generic_perform_write() calling
a NULL write_begin callback from ntfs_aops_cmpr.

[FIX]
Treat system.dos_attrib as a low-byte DOS attribute update and preserve the
existing non-DOS attribute bits in ni->std_fa. This keeps compressed and
sparse state consistent with ATTR_DATA and the mapping operations while
keeping the existing DOS attribute semantics intact.

Signed-off-by: ZhengYuan Huang <gality369@gmail.com>
Signed-off-by: Konstantin Komarov <almaz.alexandrovich@paragon-software.com>
This commit is contained in:
ZhengYuan Huang 2026-04-27 11:24:18 +08:00 committed by Konstantin Komarov
parent d62cf685d1
commit b1c1101067
No known key found for this signature in database
GPG Key ID: A9B0331F832407B6
1 changed files with 3 additions and 1 deletions
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4
fs/ntfs3/xattr.c
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@ -867,7 +867,9 @@ static noinline int ntfs_setxattr(const struct xattr_handler *handler,
if (!strcmp(name, SYSTEM_DOS_ATTRIB)) {
if (sizeof(u8) != size)
goto out;
new_fa = cpu_to_le32(*(u8 *)value);
/* system.dos_attrib only covers the low DOS attribute byte. */
new_fa = (ni->std_fa & ~cpu_to_le32(0xff)) |
cpu_to_le32(*(u8 *)value);
goto set_new_fa;
}