On Wed, Apr 17, 2024 at 12:49 AM GUO Zihua <guozihua@xxxxxxxxxx> 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
> ima_file_check+0x64/0x90
> path_openat+0x571/0x1720
> do_filp_open+0x9b/0x110
> do_sys_open+0x1bd/0x250
> do_syscall_64+0x5d/0x1d0
> entry_SYSCALL_64_after_hwframe+0x65/0xca
>
> (stack trace marked with ? is deleted)
>
> 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>
> ---
> security/integrity/ima/ima_policy.c | 2 +-
> security/selinux/ss/services.c | 2 +-
> 2 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
> index c0556907c2e6..c0cf9b6a01f0 100644
> --- a/security/integrity/ima/ima_policy.c
> +++ b/security/integrity/ima/ima_policy.c
> @@ -410,7 +410,7 @@ static struct ima_rule_entry *ima_lsm_copy_rule(struct ima_rule_entry *entry)
> * Immutable elements are copied over as pointers and data; only
> * lsm rules can change
> */
> - nentry = kmemdup(entry, sizeof(*nentry), GFP_KERNEL);
> + nentry = kmemdup(entry, sizeof(*nentry), GFP_ATOMIC);
> if (!nentry)
> return NULL;
>
> diff --git a/security/selinux/ss/services.c b/security/selinux/ss/services.c
> index e88b1b6c4adb..b7cfad1a2964 100644
> --- a/security/selinux/ss/services.c
> +++ b/security/selinux/ss/services.c
> @@ -3549,7 +3549,7 @@ int selinux_audit_rule_init(u32 field, u32 op, char *rulestr, void **vrule)
> return -EINVAL;
> }
>
> - tmprule = kzalloc(sizeof(struct selinux_audit_rule), GFP_KERNEL);
> + tmprule = kzalloc(sizeof(struct selinux_audit_rule), GFP_ATOMIC);
I would suggest passing in gfp flags from the callers and only using
GFP_ATOMIC for the particular call chain that requires atomic
allocations, or re-factoring the caller to perform the allocating
operations outside of the critical section.
Sidebar: the refactoring of the SELinux policy loading logic may have
made it possible to revisit the approaches here to permit holding a
reference to the policy from which the rule was derived so that we
don't have to return -ESTALE in this scenario.
> if (!tmprule)
> return -ENOMEM;
> context_init(&tmprule->au_ctxt);
> --
>
