On Fri, 2024-05-10 at 09:03 -0700, Casey Schaufler wrote: > On 5/6/2024 6:25 PM, GUO Zihua wrote: > > 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. > > > > Fixes: c7423dbdbc9e ("ima: Handle -ESTALE returned by ima_filter_rule_match()") > > Cc: stable@xxxxxxxxxxxxxxx > > Signed-off-by: GUO Zihua <guozihua@xxxxxxxxxx> > > Looks fine from the Smack perspective. > Reviewed-by: Casey Schaufler <casey@xxxxxxxxxxxxxxxx> Thanks, Casey. JJ? Paul?