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Fri, 5 Jul 2024 22:04:27 +0000 (GMT) Message-ID: Subject: Re: [PATCH] ima: Avoid blocking in RCU read-side critical section From: Mimi Zohar To: Roberto Sassu , stable@vger.kernel.org Cc: GUO Zihua , John Johansen , Casey Schaufler , Paul Moore , Roberto Sassu Date: Fri, 05 Jul 2024 18:04:27 -0400 In-Reply-To: <20240704104303.3330331-1-roberto.sassu@huaweicloud.com> References: <20240704104303.3330331-1-roberto.sassu@huaweicloud.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.28.5 (3.28.5-26.el8_10) Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: TC_sm4TCPCrftapOSYIocRTnc1Edmkp4 X-Proofpoint-GUID: TC_sm4TCPCrftapOSYIocRTnc1Edmkp4 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1039,Hydra:6.0.680,FMLib:17.12.28.16 definitions=2024-07-05_16,2024-07-05_01,2024-05-17_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 lowpriorityscore=0 impostorscore=0 mlxlogscore=999 clxscore=1015 adultscore=0 suspectscore=0 malwarescore=0 mlxscore=0 spamscore=0 bulkscore=0 priorityscore=1501 phishscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.19.0-2406140001 definitions=main-2407050162 On Thu, 2024-07-04 at 12:43 +0200, Roberto Sassu wrote: > From: GUO Zihua > > 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@vger.kernel.org > Signed-off-by: GUO Zihua > Acked-by: John Johansen > Reviewed-by: Mimi Zohar > Reviewed-by: Casey Schaufler > [PM: fixed missing comment, long lines, !CONFIG_IMA_LSM_RULES case] > Signed-off-by: Paul Moore > (cherry picked from commit 9a95c5bfbf02a0a7f5983280fe284a0ff0836c34) > Signed-off-by: Roberto Sassu > --- > Backporting notes: > - Remove security_audit_rule_init() documentation changes > - Add default return value parameter to call_int_hook() > in security_audit_rule_init() > - Can be backported to 6.1.x, 5.15.x, 5.10.x Thanks, Roberto. I'll post a similar one for linux-6.8.y - linux-6.4.y. Mimi