Bug 2400796 (CVE-2023-53485)

Summary:	CVE-2023-53485 kernel: fs: jfs: Fix UBSAN: array-index-out-of-bounds in dbAllocDmapLev
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 vulnerability has been identified in the Linux kernel component for the journaled file system (JFS) within the function dbAllocDmapLev(). Specifically, the leafidx variable can become negative, and then the code uses it in an array index operation dp->tree.stree[leafidx + LEAFIND] leading to damage of system availability	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 2025-10-01 12:07:53 UTC

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

fs: jfs: Fix UBSAN: array-index-out-of-bounds in dbAllocDmapLev

Syzkaller reported the following issue:

UBSAN: array-index-out-of-bounds in fs/jfs/jfs_dmap.c:1965:6
index -84 is out of range for type 's8[341]' (aka 'signed char[341]')
CPU: 1 PID: 4995 Comm: syz-executor146 Not tainted 6.4.0-rc6-syzkaller-00037-gb6dad5178cea #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/27/2023
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0x1e7/0x2d0 lib/dump_stack.c:106
 ubsan_epilogue lib/ubsan.c:217 [inline]
 __ubsan_handle_out_of_bounds+0x11c/0x150 lib/ubsan.c:348
 dbAllocDmapLev+0x3e5/0x430 fs/jfs/jfs_dmap.c:1965
 dbAllocCtl+0x113/0x920 fs/jfs/jfs_dmap.c:1809
 dbAllocAG+0x28f/0x10b0 fs/jfs/jfs_dmap.c:1350
 dbAlloc+0x658/0xca0 fs/jfs/jfs_dmap.c:874
 dtSplitUp fs/jfs/jfs_dtree.c:974 [inline]
 dtInsert+0xda7/0x6b00 fs/jfs/jfs_dtree.c:863
 jfs_create+0x7b6/0xbb0 fs/jfs/namei.c:137
 lookup_open fs/namei.c:3492 [inline]
 open_last_lookups fs/namei.c:3560 [inline]
 path_openat+0x13df/0x3170 fs/namei.c:3788
 do_filp_open+0x234/0x490 fs/namei.c:3818
 do_sys_openat2+0x13f/0x500 fs/open.c:1356
 do_sys_open fs/open.c:1372 [inline]
 __do_sys_openat fs/open.c:1388 [inline]
 __se_sys_openat fs/open.c:1383 [inline]
 __x64_sys_openat+0x247/0x290 fs/open.c:1383
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd
RIP: 0033:0x7f1f4e33f7e9
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 51 14 00 00 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 c0 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffc21129578 EFLAGS: 00000246 ORIG_RAX: 0000000000000101
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f1f4e33f7e9
RDX: 000000000000275a RSI: 0000000020000040 RDI: 00000000ffffff9c
RBP: 00007f1f4e2ff080 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f1f4e2ff110
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
 </TASK>

The bug occurs when the dbAllocDmapLev()function attempts to access
dp->tree.stree[leafidx + LEAFIND] while the leafidx value is negative.

To rectify this, the patch introduces a safeguard within the
dbAllocDmapLev() function. A check has been added to verify if leafidx is
negative. If it is, the function immediately returns an I/O error, preventing
any further execution that could potentially cause harm.

Tested via syzbot.

Comment 1 Jon Moroney 2025-10-01 18:55:32 UTC

Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2025100114-CVE-2023-53485-672c@gregkh/T