Bug 2422772 (CVE-2025-68261)

Summary:	CVE-2025-68261 kernel: Linux kernel: Denial of Service in ext4 due to a race condition
Product:	[Other] Security Response	Reporter:	OSIDB Bzimport <bzimport>
Component:	vulnerability	Assignee:	Product Security DevOps Team <prodsec-dev>
Status:	NEW ---	QA Contact:
Severity:	medium	Docs Contact:
Priority:	medium
Version:	unspecified	Keywords:	Security
Target Milestone:	---
Target Release:	---
Hardware:	All
OS:	Linux
Whiteboard:
Fixed In Version:		Doc Type:	---
Doc Text:	A flaw was discovered in the Linux kernel’s EXT4 filesystem implementation involving a race between inline data destruction and block mapping. In the function ext4_destroy_inline_data_nolock(), the inode layout is modified (clearing EXT4_INODE_INLINE_DATA and setting EXT4_INODE_EXTENTS) without holding the i_data_sem semaphore. Concurrently, another thread may execute ext4_map_blocks(), which tests the EXT4_INODE_EXTENTS flag to decide whether to call ext4_ext_map_blocks() or ext4_ind_map_blocks(). Without proper semaphore protection, ext4_ind_map_blocks() can be invoked with an inconsistent state, potentially triggering a kernel assertion and crash (BUG).	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 2025-12-16 15:03:54 UTC

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

ext4: add i_data_sem protection in ext4_destroy_inline_data_nolock()

Fix a race between inline data destruction and block mapping.

The function ext4_destroy_inline_data_nolock() changes the inode data
layout by clearing EXT4_INODE_INLINE_DATA and setting EXT4_INODE_EXTENTS.
At the same time, another thread may execute ext4_map_blocks(), which
tests EXT4_INODE_EXTENTS to decide whether to call ext4_ext_map_blocks()
or ext4_ind_map_blocks().

Without i_data_sem protection, ext4_ind_map_blocks() may receive inode
with EXT4_INODE_EXTENTS flag and triggering assert.

kernel BUG at fs/ext4/indirect.c:546!
EXT4-fs (loop2): unmounting filesystem.
invalid opcode: 0000 [#1] PREEMPT SMP KASAN NOPTI
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.12.0-1 04/01/2014
RIP: 0010:ext4_ind_map_blocks.cold+0x2b/0x5a fs/ext4/indirect.c:546

Call Trace:
 <TASK>
 ext4_map_blocks+0xb9b/0x16f0 fs/ext4/inode.c:681
 _ext4_get_block+0x242/0x590 fs/ext4/inode.c:822
 ext4_block_write_begin+0x48b/0x12c0 fs/ext4/inode.c:1124
 ext4_write_begin+0x598/0xef0 fs/ext4/inode.c:1255
 ext4_da_write_begin+0x21e/0x9c0 fs/ext4/inode.c:3000
 generic_perform_write+0x259/0x5d0 mm/filemap.c:3846
 ext4_buffered_write_iter+0x15b/0x470 fs/ext4/file.c:285
 ext4_file_write_iter+0x8e0/0x17f0 fs/ext4/file.c:679
 call_write_iter include/linux/fs.h:2271 [inline]
 do_iter_readv_writev+0x212/0x3c0 fs/read_write.c:735
 do_iter_write+0x186/0x710 fs/read_write.c:861
 vfs_iter_write+0x70/0xa0 fs/read_write.c:902
 iter_file_splice_write+0x73b/0xc90 fs/splice.c:685
 do_splice_from fs/splice.c:763 [inline]
 direct_splice_actor+0x10f/0x170 fs/splice.c:950
 splice_direct_to_actor+0x33a/0xa10 fs/splice.c:896
 do_splice_direct+0x1a9/0x280 fs/splice.c:1002
 do_sendfile+0xb13/0x12c0 fs/read_write.c:1255
 __do_sys_sendfile64 fs/read_write.c:1323 [inline]
 __se_sys_sendfile64 fs/read_write.c:1309 [inline]
 __x64_sys_sendfile64+0x1cf/0x210 fs/read_write.c:1309
 do_syscall_x64 arch/x86/entry/common.c:51 [inline]
 do_syscall_64+0x35/0x80 arch/x86/entry/common.c:81
 entry_SYSCALL_64_after_hwframe+0x6e/0xd8

Comment 1 Alexander B 2025-12-16 21:25:04 UTC

Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2025121614-CVE-2025-68261-4e23@gregkh/T