[PATCH v3] ima: Avoid blocking in RCU read-side critical section

Casey Schaufler casey at schaufler-ca.com
Fri May 10 16:03:35 UTC 2024


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 at vger.kernel.org
> Signed-off-by: GUO Zihua <guozihua at huawei.com>

Looks fine from the Smack perspective.
Reviewed-by: Casey Schaufler <casey at schaufler-ca.com>

> ---
>
> v3:
>   ima_lsm_copy_rule takes a GFP flag as input as well.
> 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 | 15 +++++++++------
>  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, 32 insertions(+), 21 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..09da8e639239 100644
> --- a/security/integrity/ima/ima_policy.c
> +++ b/security/integrity/ima/ima_policy.c
> @@ -401,7 +401,8 @@ static void ima_free_rule(struct ima_rule_entry *entry)
>  	kfree(entry);
>  }
>  
> -static struct ima_rule_entry *ima_lsm_copy_rule(struct ima_rule_entry *entry)
> +static struct ima_rule_entry *ima_lsm_copy_rule(struct ima_rule_entry *entry,
> +						gfp_t gfp)
>  {
>  	struct ima_rule_entry *nentry;
>  	int i;
> @@ -410,7 +411,7 @@ 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);
>  	if (!nentry)
>  		return NULL;
>  
> @@ -425,7 +426,8 @@ 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);
>  		if (!nentry->lsm[i].rule)
>  			pr_warn("rule for LSM \'%s\' is undefined\n",
>  				nentry->lsm[i].args_p);
> @@ -438,7 +440,7 @@ static int ima_lsm_update_rule(struct ima_rule_entry *entry)
>  	int i;
>  	struct ima_rule_entry *nentry;
>  
> -	nentry = ima_lsm_copy_rule(entry);
> +	nentry = ima_lsm_copy_rule(entry, GFP_KERNEL);
>  	if (!nentry)
>  		return -ENOMEM;
>  
> @@ -664,7 +666,7 @@ static bool ima_match_rules(struct ima_rule_entry *rule,
>  		}
>  
>  		if (rc == -ESTALE && !rule_reinitialized) {
> -			lsm_rule = ima_lsm_copy_rule(rule);
> +			lsm_rule = ima_lsm_copy_rule(rule, GFP_ATOMIC);
>  			if (lsm_rule) {
>  				rule_reinitialized = true;
>  				goto retry;
> @@ -1140,7 +1142,8 @@ 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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