CVE-2024-40947

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

ima: Avoid blocking in RCU read-side critical section

A panic happens in ima_match_policy:

BUG: unable to handle kernel NULL pointer dereference at 0000000000000010

PGD 42f873067 P4D 0

Oops: 0000 [#1] SMP NOPTI

CPU: 5 PID: 1286325 Comm: kubeletmonit.sh

Kdump: loaded Tainted: P

Hardware name: QEMU Standard PC (i440FX + PIIX, 1996),

BIOS 0.0.0 02/06/2015

RIP: 0010:ima_match_policy+0x84/0x450

Code: 49 89 fc 41 89 cf 31 ed 89 44 24 14 eb 1c 44 39

7b 18 74 26 41 83 ff 05 74 20 48 8b 1b 48 3b 1d

f2 b9 f4 00 0f 84 9c 01 00 00 <44> 85 73 10 74 ea

44 8b 6b 14 41 f6 c5 01 75 d4 41 f6 c5 02 74 0f

RSP: 0018:ff71570009e07a80 EFLAGS: 00010207

RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000200

RDX: ffffffffad8dc7c0 RSI: 0000000024924925 RDI: ff3e27850dea2000

RBP: 0000000000000000 R08: 0000000000000000 R09: ffffffffabfce739

R10: ff3e27810cc42400 R11: 0000000000000000 R12: ff3e2781825ef970

R13: 00000000ff3e2785 R14: 000000000000000c R15: 0000000000000001

FS: 00007f5195b51740(0000)

GS:ff3e278b12d40000(0000) knlGS:0000000000000000

CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033

CR2: 0000000000000010 CR3: 0000000626d24002 CR4: 0000000000361ee0

DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000

DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400

Call Trace:

ima_get_action+0x22/0x30

process_measurement+0xb0/0x830

? page_add_file_rmap+0x15/0x170

? alloc_set_pte+0x269/0x4c0

? prep_new_page+0x81/0x140

? simple_xattr_get+0x75/0xa0

? selinux_file_open+0x9d/0xf0

ima_file_check+0x64/0x90

path_openat+0x571/0x1720

do_filp_open+0x9b/0x110

? page_counter_try_charge+0x57/0xc0

? files_cgroup_alloc_fd+0x38/0x60

? __alloc_fd+0xd4/0x250

? do_sys_open+0x1bd/0x250

do_sys_open+0x1bd/0x250

do_syscall_64+0x5d/0x1d0

entry_SYSCALL_64_after_hwframe+0x65/0xca

Commit c7423dbdbc9e ("ima: Handle -ESTALE returned by

ima_filter_rule_match()") introduced call to ima_lsm_copy_rule within a

RCU read-side critical section which contains kmalloc with GFP_KERNEL.

This implies a possible sleep and violates limitations of RCU read-side

critical sections on non-PREEMPT systems.

Sleeping within RCU read-side critical section might cause

synchronize_rcu() returning early and break RCU protection, allowing a

UAF to happen.

The root cause of this issue could be described as follows:

| Thread A | Thread B |

| |ima_match_policy |

| | rcu_read_lock |

|ima_lsm_update_rule | |

| synchronize_rcu | |

| | kmalloc(GFP_KERNEL)|

| | sleep |

==> synchronize_rcu returns early

| kfree(entry) | |

| | entry = entry->next|

==> UAF happens and entry now becomes NULL (or could be anything).

| | entry->action |

==> Accessing entry might cause panic.

To fix this issue, we are converting all kmalloc that is called within

RCU read-side critical section to use GFP_ATOMIC.

[PM: fixed missing comment, long lines, !CONFIG_IMA_LSM_RULES case]