[PATCH v2] ima: Avoid blocking in RCU read-side critical section
Casey Schaufler
casey at schaufler-ca.com
Sun Apr 28 16:39:53 UTC 2024
On 4/28/2024 2:10 AM, GUO Zihua wrote:
> A panic happens in ima_match_policy:
You need to add linux-security-module at vger.kernel.org to your CC list.
>
> 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 at vger.kernel.org
> Signed-off-by: GUO Zihua <guozihua at huawei.com>
> ---
>
> v2:
> Changed the audit_rule_init security hook to accept a new GFP flag, as
> per Stephen's suggestion.
>
> ---
> include/linux/lsm_hook_defs.h | 2 +-
> include/linux/security.h | 5 +++--
> kernel/auditfilter.c | 5 +++--
> security/apparmor/audit.c | 6 +++---
> security/apparmor/include/audit.h | 2 +-
> security/integrity/ima/ima_policy.c | 8 +++++---
> security/security.c | 6 ++++--
> security/selinux/include/audit.h | 4 +++-
> security/selinux/ss/services.c | 5 +++--
> security/smack/smack_lsm.c | 3 ++-
> 10 files changed, 28 insertions(+), 18 deletions(-)
>
> diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h
> index 334e00efbde4..7e539f6f8c67 100644
> --- a/include/linux/lsm_hook_defs.h
> +++ b/include/linux/lsm_hook_defs.h
> @@ -412,7 +412,7 @@ LSM_HOOK(void, LSM_RET_VOID, key_post_create_or_update, struct key *keyring,
>
> #ifdef CONFIG_AUDIT
> LSM_HOOK(int, 0, audit_rule_init, u32 field, u32 op, char *rulestr,
> - void **lsmrule)
> + void **lsmrule, gfp_t gfp)
> LSM_HOOK(int, 0, audit_rule_known, struct audit_krule *krule)
> LSM_HOOK(int, 0, audit_rule_match, u32 secid, u32 field, u32 op, void *lsmrule)
> LSM_HOOK(void, LSM_RET_VOID, audit_rule_free, void *lsmrule)
> diff --git a/include/linux/security.h b/include/linux/security.h
> index 41a8f667bdfa..5122e3ad83b1 100644
> --- a/include/linux/security.h
> +++ b/include/linux/security.h
> @@ -2048,7 +2048,8 @@ static inline void security_key_post_create_or_update(struct key *keyring,
>
> #ifdef CONFIG_AUDIT
> #ifdef CONFIG_SECURITY
> -int security_audit_rule_init(u32 field, u32 op, char *rulestr, void **lsmrule);
> +int security_audit_rule_init(u32 field, u32 op, char *rulestr, void **lsmrule,
> + gfp_t gfp);
> int security_audit_rule_known(struct audit_krule *krule);
> int security_audit_rule_match(u32 secid, u32 field, u32 op, void *lsmrule);
> void security_audit_rule_free(void *lsmrule);
> @@ -2056,7 +2057,7 @@ void security_audit_rule_free(void *lsmrule);
> #else
>
> static inline int security_audit_rule_init(u32 field, u32 op, char *rulestr,
> - void **lsmrule)
> + void **lsmrule, gfp_t gfp)
> {
> return 0;
> }
> diff --git a/kernel/auditfilter.c b/kernel/auditfilter.c
> index be8c680121e4..d6ef4f4f9cba 100644
> --- a/kernel/auditfilter.c
> +++ b/kernel/auditfilter.c
> @@ -529,7 +529,8 @@ static struct audit_entry *audit_data_to_entry(struct audit_rule_data *data,
> entry->rule.buflen += f_val;
> f->lsm_str = str;
> err = security_audit_rule_init(f->type, f->op, str,
> - (void **)&f->lsm_rule);
> + (void **)&f->lsm_rule,
> + GFP_KERNEL);
> /* Keep currently invalid fields around in case they
> * become valid after a policy reload. */
> if (err == -EINVAL) {
> @@ -799,7 +800,7 @@ static inline int audit_dupe_lsm_field(struct audit_field *df,
>
> /* our own (refreshed) copy of lsm_rule */
> ret = security_audit_rule_init(df->type, df->op, df->lsm_str,
> - (void **)&df->lsm_rule);
> + (void **)&df->lsm_rule, GFP_KERNEL);
> /* Keep currently invalid fields around in case they
> * become valid after a policy reload. */
> if (ret == -EINVAL) {
> diff --git a/security/apparmor/audit.c b/security/apparmor/audit.c
> index 45beb1c5f747..6b5181c668b5 100644
> --- a/security/apparmor/audit.c
> +++ b/security/apparmor/audit.c
> @@ -217,7 +217,7 @@ void aa_audit_rule_free(void *vrule)
> }
> }
>
> -int aa_audit_rule_init(u32 field, u32 op, char *rulestr, void **vrule)
> +int aa_audit_rule_init(u32 field, u32 op, char *rulestr, void **vrule, gfp_t gfp)
> {
> struct aa_audit_rule *rule;
>
> @@ -230,14 +230,14 @@ int aa_audit_rule_init(u32 field, u32 op, char *rulestr, void **vrule)
> return -EINVAL;
> }
>
> - rule = kzalloc(sizeof(struct aa_audit_rule), GFP_KERNEL);
> + rule = kzalloc(sizeof(struct aa_audit_rule), gfp);
>
> if (!rule)
> return -ENOMEM;
>
> /* Currently rules are treated as coming from the root ns */
> rule->label = aa_label_parse(&root_ns->unconfined->label, rulestr,
> - GFP_KERNEL, true, false);
> + gfp, true, false);
> if (IS_ERR(rule->label)) {
> int err = PTR_ERR(rule->label);
> aa_audit_rule_free(rule);
> diff --git a/security/apparmor/include/audit.h b/security/apparmor/include/audit.h
> index acbb03b9bd25..0c8cc86b417b 100644
> --- a/security/apparmor/include/audit.h
> +++ b/security/apparmor/include/audit.h
> @@ -200,7 +200,7 @@ static inline int complain_error(int error)
> }
>
> void aa_audit_rule_free(void *vrule);
> -int aa_audit_rule_init(u32 field, u32 op, char *rulestr, void **vrule);
> +int aa_audit_rule_init(u32 field, u32 op, char *rulestr, void **vrule, gfp_t gfp);
> int aa_audit_rule_known(struct audit_krule *rule);
> int aa_audit_rule_match(u32 sid, u32 field, u32 op, void *vrule);
>
> diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
> index c0556907c2e6..216ffe388ce5 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;
>
> @@ -425,7 +425,8 @@ static struct ima_rule_entry *ima_lsm_copy_rule(struct ima_rule_entry *entry)
>
> ima_filter_rule_init(nentry->lsm[i].type, Audit_equal,
> nentry->lsm[i].args_p,
> - &nentry->lsm[i].rule);
> + &nentry->lsm[i].rule,
> + GFP_ATOMIC);
> if (!nentry->lsm[i].rule)
> pr_warn("rule for LSM \'%s\' is undefined\n",
> nentry->lsm[i].args_p);
> @@ -1140,7 +1141,8 @@ static int ima_lsm_rule_init(struct ima_rule_entry *entry,
> entry->lsm[lsm_rule].type = audit_type;
> result = ima_filter_rule_init(entry->lsm[lsm_rule].type, Audit_equal,
> entry->lsm[lsm_rule].args_p,
> - &entry->lsm[lsm_rule].rule);
> + &entry->lsm[lsm_rule].rule,
> + GFP_KERNEL);
> if (!entry->lsm[lsm_rule].rule) {
> pr_warn("rule for LSM \'%s\' is undefined\n",
> entry->lsm[lsm_rule].args_p);
> diff --git a/security/security.c b/security/security.c
> index 0a9a0ac3f266..4fd3c839353e 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -5331,15 +5331,17 @@ void security_key_post_create_or_update(struct key *keyring, struct key *key,
> * @op: rule operator
> * @rulestr: rule context
> * @lsmrule: receive buffer for audit rule struct
> + * @gfp: GFP flag used for kmalloc
> *
> * Allocate and initialize an LSM audit rule structure.
> *
> * Return: Return 0 if @lsmrule has been successfully set, -EINVAL in case of
> * an invalid rule.
> */
> -int security_audit_rule_init(u32 field, u32 op, char *rulestr, void **lsmrule)
> +int security_audit_rule_init(u32 field, u32 op, char *rulestr, void **lsmrule,
> + gfp_t gfp)
> {
> - return call_int_hook(audit_rule_init, field, op, rulestr, lsmrule);
> + return call_int_hook(audit_rule_init, field, op, rulestr, lsmrule, gfp);
> }
>
> /**
> diff --git a/security/selinux/include/audit.h b/security/selinux/include/audit.h
> index 52aca71210b4..29c7d4c86f6d 100644
> --- a/security/selinux/include/audit.h
> +++ b/security/selinux/include/audit.h
> @@ -21,12 +21,14 @@
> * @op: the operator the rule uses
> * @rulestr: the text "target" of the rule
> * @rule: pointer to the new rule structure returned via this
> + * @gfp: GFP flag used for kmalloc
> *
> * Returns 0 if successful, -errno if not. On success, the rule structure
> * will be allocated internally. The caller must free this structure with
> * selinux_audit_rule_free() after use.
> */
> -int selinux_audit_rule_init(u32 field, u32 op, char *rulestr, void **rule);
> +int selinux_audit_rule_init(u32 field, u32 op, char *rulestr, void **rule,
> + gfp_t gfp);
>
> /**
> * selinux_audit_rule_free - free an selinux audit rule structure.
> diff --git a/security/selinux/ss/services.c b/security/selinux/ss/services.c
> index e88b1b6c4adb..ded250e525e9 100644
> --- a/security/selinux/ss/services.c
> +++ b/security/selinux/ss/services.c
> @@ -3508,7 +3508,8 @@ void selinux_audit_rule_free(void *vrule)
> }
> }
>
> -int selinux_audit_rule_init(u32 field, u32 op, char *rulestr, void **vrule)
> +int selinux_audit_rule_init(u32 field, u32 op, char *rulestr, void **vrule,
> + gfp_t gfp)
> {
> struct selinux_state *state = &selinux_state;
> struct selinux_policy *policy;
> @@ -3549,7 +3550,7 @@ 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);
> if (!tmprule)
> return -ENOMEM;
> context_init(&tmprule->au_ctxt);
> diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
> index 146667937811..a4943628d75a 100644
> --- a/security/smack/smack_lsm.c
> +++ b/security/smack/smack_lsm.c
> @@ -4696,7 +4696,8 @@ static int smack_post_notification(const struct cred *w_cred,
> * Prepare to audit cases where (@field @op @rulestr) is true.
> * The label to be audited is created if necessay.
> */
> -static int smack_audit_rule_init(u32 field, u32 op, char *rulestr, void **vrule)
> +static int smack_audit_rule_init(u32 field, u32 op, char *rulestr, void **vrule,
> + gfp_t gfp)
> {
> struct smack_known *skp;
> char **rule = (char **)vrule;
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