Bug 2540455 (CVE-2026-97439)

Summary:	CVE-2026-97439 kernel: fs/ntfs3: preserve non-DOS attribute bits in system.dos_attrib
Product:	[Other] Security Response	Reporter:	OSIDB Bzimport <bzimport>
Component:	vulnerability	Assignee:	Product Security <prodsec-ir-bot>
Status:	NEW ---	QA Contact:
Severity:	medium	Docs Contact:
Priority:	medium
Version:	unspecified	CC:	akhatavk, aos-team-art-private, asdas, dpaolell, jdelft, jupierce, lgarciaa, mbiarnes, ppalepu, ppostler, prdhamdh, rhel-process-autobot, sghai, sidsharm, suppawar, vlaad, watson-tool-maintainers
Target Milestone:	---	Keywords:	Security
Target Release:	---
Hardware:	All
OS:	Linux
Whiteboard:
Fixed In Version:		Doc Type:	---
Doc Text:	A flaw was found in the Linux kernel's NTFS3 file system. A local user can cause a Denial of Service (DoS) by manipulating extended file attributes on a mounted NTFS volume. Improper attribute handling clears internal compression flags without synchronizing file mapping operations, triggering a kernel null pointer dereference and system crash during subsequent write operations.	Story Points:	---
Clone Of:		Environment:
Last Closed:		Type:	---
Regression:	---	Mount Type:	---
Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:

Description OSIDB Bzimport 2026-09-24 16:54:09 UTC

In the Linux kernel, the following vulnerability has been resolved:

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

[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.

Comment 1 Mauro Matteo Cascella 2026-09-29 14:29:36 UTC

Upstream advisory:
https://git.kernel.org/pub/scm/linux/security/vulns.git/plain/cve/published/2026/CVE-2026-97439.mbox