Subject: CVE-2024-43898: ext4: sanity check for NULL pointer after ext4_force_shutdown

From: Greg Kroah-Hartman <[email-masked]>

Description
===========

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

ext4: sanity check for NULL pointer after ext4_force_shutdown

Test case: 2 threads write short inline data to a file.
In ext4_page_mkwrite the resulting inline data is converted.
Handling ext4_grp_locked_error with description "block bitmap
and bg descriptor inconsistent: X vs Y free clusters" calls
ext4_force_shutdown. The conversion clears
EXT4_STATE_MAY_INLINE_DATA but fails for
ext4_destroy_inline_data_nolock and ext4_mark_iloc_dirty due
to ext4_forced_shutdown. The restoration of inline data fails
for the same reason not setting EXT4_STATE_MAY_INLINE_DATA.
Without the flag set a regular process path in ext4_da_write_end
follows trying to dereference page folio private pointer that has
not been set. The fix calls early return with -EIO error shall the
pointer to private be NULL.

Sample crash report:

Unable to handle kernel paging request at virtual address dfff800000000004
KASAN: null-ptr-deref in range [0x0000000000000020-0x0000000000000027]
Mem abort info:
  ESR = 0x0000000096000005
  EC = 0x25: DABT (current EL), IL = 32 bits
  SET = 0, FnV = 0
  EA = 0, S1PTW = 0
  FSC = 0x05: level 1 translation fault
Data abort info:
  ISV = 0, ISS = 0x00000005, ISS2 = 0x00000000
  CM = 0, WnR = 0, TnD = 0, TagAccess = 0
  GCS = 0, Overlay = 0, DirtyBit = 0, Xs = 0
[dfff800000000004] address between user and kernel address ranges
Internal error: Oops: 0000000096000005 [#1] PREEMPT SMP
Modules linked in:
CPU: 1 PID: 20274 Comm: syz-executor185 Not tainted 6.9.0-rc7-syzkaller-gfda5695d692c #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/27/2024
pstate: 80400005 (Nzcv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
pc : __block_commit_write+0x64/0x2b0 fs/buffer.c:2167
lr : __block_commit_write+0x3c/0x2b0 fs/buffer.c:2160
sp : ffff8000a1957600
x29: ffff8000a1957610 x28: dfff800000000000 x27: ffff0000e30e34b0
x26: 0000000000000000 x25: dfff800000000000 x24: dfff800000000000
x23: fffffdffc397c9e0 x22: 0000000000000020 x21: 0000000000000020
x20: 0000000000000040 x19: fffffdffc397c9c0 x18: 1fffe000367bd196
x17: ffff80008eead000 x16: ffff80008ae89e3c x15: 00000000200000c0
x14: 1fffe0001cbe4e04 x13: 0000000000000000 x12: 0000000000000000
x11: 0000000000000001 x10: 0000000000ff0100 x9 : 0000000000000000
x8 : 0000000000000004 x7 : 0000000000000000 x6 : 0000000000000000
x5 : fffffdffc397c9c0 x4 : 0000000000000020 x3 : 0000000000000020
x2 : 0000000000000040 x1 : 0000000000000020 x0 : fffffdffc397c9c0
Call trace:
 __block_commit_write+0x64/0x2b0 fs/buffer.c:2167
 block_write_end+0xb4/0x104 fs/buffer.c:2253
 ext4_da_do_write_end fs/ext4/inode.c:2955 [inline]
 ext4_da_write_end+0x2c4/0xa40 fs/ext4/inode.c:3028
 generic_perform_write+0x394/0x588 mm/filemap.c:3985
 ext4_buffered_write_iter+0x2c0/0x4ec fs/ext4/file.c:299
 ext4_file_write_iter+0x188/0x1780
 call_write_iter include/linux/fs.h:2110 [inline]
 new_sync_write fs/read_write.c:497 [inline]
 vfs_write+0x968/0xc3c fs/read_write.c:590
 ksys_write+0x15c/0x26c fs/read_write.c:643
 __do_sys_write fs/read_write.c:655 [inline]
 __se_sys_write fs/read_write.c:652 [inline]
 __arm64_sys_write+0x7c/0x90 fs/read_write.c:652
 __invoke_syscall arch/arm64/kernel/syscall.c:34 [inline]
 invoke_syscall+0x98/0x2b8 arch/arm64/kernel/syscall.c:48
 el0_svc_common+0x130/0x23c arch/arm64/kernel/syscall.c:133
 do_el0_svc+0x48/0x58 arch/arm64/kernel/syscall.c:152
 el0_svc+0x54/0x168 arch/arm64/kernel/entry-common.c:712
 el0t_64_sync_handler+0x84/0xfc arch/arm64/kernel/entry-common.c:730
 el0t_64_sync+0x190/0x194 arch/arm64/kernel/entry.S:598
Code: 97f85911 f94002da 91008356 d343fec8 (38796908)
---[ end trace 0000000000000000 ]---
----------------
Code disassembly (best guess):
   0:	97f85911 	bl	0xffffffffffe16444
   4:	f94002da 	ldr	x26, [x22]
   8:	91008356 	add	x22, x26, #0x20
   c:	d343fec8 	lsr	x8, x22, #3
* 10:	38796908 	ldrb	w8, [x8, x25] <-- trapping instruction

The Linux kernel CVE team has assigned CVE-2024-43898 to this issue.

Affected and fixed versions
===========================

	Fixed in 6.6.47 with commit 3f6bbe6e07e5
	Fixed in 6.10.5 with commit f619876ccbfd
	Fixed in 6.11-rc1 with commit 83f4414b8f84

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2024-43898
will be updated if fixes are backported, please check that for the most
up to date information about this issue.

Affected files
==============

The file(s) affected by this issue are:
	fs/buffer.c
	fs/ext4/inode.c

Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/3f6bbe6e07e5239294ecc3d2efa70d1f98aed52e
	https://git.kernel.org/stable/c/f619876ccbfd329ae785fe5d3289b9dcd6eb5901
	https://git.kernel.org/stable/c/83f4414b8f84249d538905825b088ff3ae555652