apparmor: make it so work buffers can be allocated from atomic context

In some situations AppArmor needs to be able to use its work buffers
from atomic context. Add the ability to specify when in atomic context
and hold a set of work buffers in reserve for atomic context to
reduce the chance that a large work buffer allocation will need to
be done.

Fixes: df323337 ("apparmor: Use a memory pool instead per-CPU caches")
Signed-off-by: John Johansen <john.johansen@canonical.com>

security/apparmor/domain.c

@@ -896,7 +896,7 @@ int apparmor_bprm_set_creds(struct linux_binprm *bprm)
 		ctx->nnp = aa_get_label(label);
 
 	/* buffer freed below, name is pointer into buffer */
-	buffer = aa_get_buffer();
+	buffer = aa_get_buffer(false);
 	if (!buffer) {
 		error = -ENOMEM;
 		goto done;

security/apparmor/file.c

@@ -336,7 +336,7 @@ int aa_path_perm(const char *op, struct aa_label *label,
 
 	flags |= PATH_DELEGATE_DELETED | (S_ISDIR(cond->mode) ? PATH_IS_DIR :
 								0);
-	buffer = aa_get_buffer();
+	buffer = aa_get_buffer(false);
 	if (!buffer)
 		return -ENOMEM;
 	error = fn_for_each_confined(label, profile,
@@ -481,8 +481,8 @@ int aa_path_link(struct aa_label *label, struct dentry *old_dentry,
 	int error;
 
 	/* buffer freed below, lname is pointer in buffer */
-	buffer = aa_get_buffer();
-	buffer2 = aa_get_buffer();
+	buffer = aa_get_buffer(false);
+	buffer2 = aa_get_buffer(false);
 	error = -ENOMEM;
 	if (!buffer || !buffer2)
 		goto out;
@@ -519,7 +519,7 @@ static void update_file_ctx(struct aa_file_ctx *fctx, struct aa_label *label,
 
 static int __file_path_perm(const char *op, struct aa_label *label,
 			    struct aa_label *flabel, struct file *file,
-			    u32 request, u32 denied)
+			    u32 request, u32 denied, bool in_atomic)
 {
 	struct aa_profile *profile;
 	struct aa_perms perms = {};
@@ -536,7 +536,7 @@ static int __file_path_perm(const char *op, struct aa_label *label,
 		return 0;
 
 	flags = PATH_DELEGATE_DELETED | (S_ISDIR(cond.mode) ? PATH_IS_DIR : 0);
-	buffer = aa_get_buffer();
+	buffer = aa_get_buffer(in_atomic);
 	if (!buffer)
 		return -ENOMEM;
 
@@ -604,11 +604,12 @@ static int __file_sock_perm(const char *op, struct aa_label *label,
  * @label: label being enforced   (NOT NULL)
  * @file: file to revalidate access permissions on  (NOT NULL)
  * @request: requested permissions
+ * @in_atomic: whether allocations need to be done in atomic context
  *
  * Returns: %0 if access allowed else error
  */
 int aa_file_perm(const char *op, struct aa_label *label, struct file *file,
-		 u32 request)
+		 u32 request, bool in_atomic)
 {
 	struct aa_file_ctx *fctx;
 	struct aa_label *flabel;
@@ -641,7 +642,7 @@ int aa_file_perm(const char *op, struct aa_label *label, struct file *file,
 
 	if (file->f_path.mnt && path_mediated_fs(file->f_path.dentry))
 		error = __file_path_perm(op, label, flabel, file, request,
-					 denied);
+					 denied, in_atomic);
 
 	else if (S_ISSOCK(file_inode(file)->i_mode))
 		error = __file_sock_perm(op, label, flabel, file, request,
@@ -669,7 +670,8 @@ static void revalidate_tty(struct aa_label *label)
 					     struct tty_file_private, list);
 		file = file_priv->file;
 
-		if (aa_file_perm(OP_INHERIT, label, file, MAY_READ | MAY_WRITE))
+		if (aa_file_perm(OP_INHERIT, label, file, MAY_READ | MAY_WRITE,
+				 IN_ATOMIC))
 			drop_tty = 1;
 	}
 	spin_unlock(&tty->files_lock);
@@ -683,7 +685,8 @@ static int match_file(const void *p, struct file *file, unsigned int fd)
 {
 	struct aa_label *label = (struct aa_label *)p;
 
-	if (aa_file_perm(OP_INHERIT, label, file, aa_map_file_to_perms(file)))
+	if (aa_file_perm(OP_INHERIT, label, file, aa_map_file_to_perms(file),
+			 IN_ATOMIC))
 		return fd + 1;
 	return 0;
 }

security/apparmor/include/file.h

@@ -201,7 +201,7 @@ int aa_path_link(struct aa_label *label, struct dentry *old_dentry,
 		 const struct path *new_dir, struct dentry *new_dentry);
 
 int aa_file_perm(const char *op, struct aa_label *label, struct file *file,
-		 u32 request);
+		 u32 request, bool in_atomic);
 
 void aa_inherit_files(const struct cred *cred, struct files_struct *files);
 

security/apparmor/include/path.h

@@ -29,7 +29,8 @@ int aa_path_name(const struct path *path, int flags, char *buffer,
 		 const char **name, const char **info,
 		 const char *disconnected);
 
-char *aa_get_buffer(void);
+#define IN_ATOMIC true
+char *aa_get_buffer(bool in_atomic);
 void aa_put_buffer(char *buf);
 
 #endif /* __AA_PATH_H */

security/apparmor/lsm.c

@@ -53,6 +53,10 @@ union aa_buffer {
 	char buffer[1];
 };
 
+#define RESERVE_COUNT 2
+static int reserve_count = RESERVE_COUNT;
+static int buffer_count;
+
 static LIST_HEAD(aa_global_buffers);
 static DEFINE_SPINLOCK(aa_buffers_lock);
 
@@ -452,7 +456,8 @@ static void apparmor_file_free_security(struct file *file)
 		aa_put_label(rcu_access_pointer(ctx->label));
 }
 
-static int common_file_perm(const char *op, struct file *file, u32 mask)
+static int common_file_perm(const char *op, struct file *file, u32 mask,
+			    bool in_atomic)
 {
 	struct aa_label *label;
 	int error = 0;
@@ -462,7 +467,7 @@ static int common_file_perm(const char *op, struct file *file, u32 mask)
 		return -EACCES;
 
 	label = __begin_current_label_crit_section();
-	error = aa_file_perm(op, label, file, mask);
+	error = aa_file_perm(op, label, file, mask, in_atomic);
 	__end_current_label_crit_section(label);
 
 	return error;
@@ -470,12 +475,13 @@ static int common_file_perm(const char *op, struct file *file, u32 mask)
 
 static int apparmor_file_receive(struct file *file)
 {
-	return common_file_perm(OP_FRECEIVE, file, aa_map_file_to_perms(file));
+	return common_file_perm(OP_FRECEIVE, file, aa_map_file_to_perms(file),
+				false);
 }
 
 static int apparmor_file_permission(struct file *file, int mask)
 {
-	return common_file_perm(OP_FPERM, file, mask);
+	return common_file_perm(OP_FPERM, file, mask, false);
 }
 
 static int apparmor_file_lock(struct file *file, unsigned int cmd)
@@ -485,11 +491,11 @@ static int apparmor_file_lock(struct file *file, unsigned int cmd)
 	if (cmd == F_WRLCK)
 		mask |= MAY_WRITE;
 
-	return common_file_perm(OP_FLOCK, file, mask);
+	return common_file_perm(OP_FLOCK, file, mask, false);
 }
 
 static int common_mmap(const char *op, struct file *file, unsigned long prot,
-		       unsigned long flags)
+		       unsigned long flags, bool in_atomic)
 {
 	int mask = 0;
 
@@ -507,20 +513,21 @@ static int common_mmap(const char *op, struct file *file, unsigned long prot,
 	if (prot & PROT_EXEC)
 		mask |= AA_EXEC_MMAP;
 
-	return common_file_perm(op, file, mask);
+	return common_file_perm(op, file, mask, in_atomic);
 }
 
 static int apparmor_mmap_file(struct file *file, unsigned long reqprot,
 			      unsigned long prot, unsigned long flags)
 {
-	return common_mmap(OP_FMMAP, file, prot, flags);
+	return common_mmap(OP_FMMAP, file, prot, flags, GFP_ATOMIC);
 }
 
 static int apparmor_file_mprotect(struct vm_area_struct *vma,
 				  unsigned long reqprot, unsigned long prot)
 {
 	return common_mmap(OP_FMPROT, vma->vm_file, prot,
-			   !(vma->vm_flags & VM_SHARED) ? MAP_PRIVATE : 0);
+			   !(vma->vm_flags & VM_SHARED) ? MAP_PRIVATE : 0,
+			   false);
 }
 
 static int apparmor_sb_mount(const char *dev_name, const struct path *path,
@@ -1571,24 +1578,36 @@ static int param_set_mode(const char *val, const struct kernel_param *kp)
 	return 0;
 }
 
-char *aa_get_buffer(void)
+char *aa_get_buffer(bool in_atomic)
 {
 	union aa_buffer *aa_buf;
 	bool try_again = true;
+	gfp_t flags = (GFP_KERNEL | __GFP_RETRY_MAYFAIL | __GFP_NOWARN);
 
 retry:
 	spin_lock(&aa_buffers_lock);
-	if (!list_empty(&aa_global_buffers)) {
+	if (buffer_count > reserve_count ||
+	    (in_atomic && !list_empty(&aa_global_buffers))) {
 		aa_buf = list_first_entry(&aa_global_buffers, union aa_buffer,
 					  list);
 		list_del(&aa_buf->list);
+		buffer_count--;
 		spin_unlock(&aa_buffers_lock);
 		return &aa_buf->buffer[0];
 	}
+	if (in_atomic) {
+		/*
+		 * out of reserve buffers and in atomic context so increase
+		 * how many buffers to keep in reserve
+		 */
+		reserve_count++;
+		flags = GFP_ATOMIC;
+	}
 	spin_unlock(&aa_buffers_lock);
 
-	aa_buf = kmalloc(aa_g_path_max, GFP_KERNEL | __GFP_RETRY_MAYFAIL |
-			 __GFP_NOWARN);
+	if (!in_atomic)
+		might_sleep();
+	aa_buf = kmalloc(aa_g_path_max, flags);
 	if (!aa_buf) {
 		if (try_again) {
 			try_again = false;
@@ -1610,6 +1629,7 @@ void aa_put_buffer(char *buf)
 
 	spin_lock(&aa_buffers_lock);
 	list_add(&aa_buf->list, &aa_global_buffers);
+	buffer_count++;
 	spin_unlock(&aa_buffers_lock);
 }
 
@@ -1661,9 +1681,9 @@ static int __init alloc_buffers(void)
 	 * disabled early at boot if aa_g_path_max is extremly high.
 	 */
 	if (num_online_cpus() > 1)
-		num = 4;
+		num = 4 + RESERVE_COUNT;
 	else
-		num = 2;
+		num = 2 + RESERVE_COUNT;
 
 	for (i = 0; i < num; i++) {
 

security/apparmor/mount.c

@@ -412,7 +412,7 @@ int aa_remount(struct aa_label *label, const struct path *path,
 
 	binary = path->dentry->d_sb->s_type->fs_flags & FS_BINARY_MOUNTDATA;
 
-	buffer = aa_get_buffer();
+	buffer = aa_get_buffer(false);
 	if (!buffer)
 		return -ENOMEM;
 	error = fn_for_each_confined(label, profile,
@@ -443,8 +443,8 @@ int aa_bind_mount(struct aa_label *label, const struct path *path,
 	if (error)
 		return error;
 
-	buffer = aa_get_buffer();
-	old_buffer = aa_get_buffer();
+	buffer = aa_get_buffer(false);
+	old_buffer = aa_get_buffer(false);
 	error = -ENOMEM;
 	if (!buffer || old_buffer)
 		goto out;
@@ -474,7 +474,7 @@ int aa_mount_change_type(struct aa_label *label, const struct path *path,
 	flags &= (MS_REC | MS_SILENT | MS_SHARED | MS_PRIVATE | MS_SLAVE |
 		  MS_UNBINDABLE);
 
-	buffer = aa_get_buffer();
+	buffer = aa_get_buffer(false);
 	if (!buffer)
 		return -ENOMEM;
 	error = fn_for_each_confined(label, profile,
@@ -503,8 +503,8 @@ int aa_move_mount(struct aa_label *label, const struct path *path,
 	if (error)
 		return error;
 
-	buffer = aa_get_buffer();
-	old_buffer = aa_get_buffer();
+	buffer = aa_get_buffer(false);
+	old_buffer = aa_get_buffer(false);
 	error = -ENOMEM;
 	if (!buffer || !old_buffer)
 		goto out;
@@ -554,13 +554,13 @@ int aa_new_mount(struct aa_label *label, const char *dev_name,
 		}
 	}
 
-	buffer = aa_get_buffer();
+	buffer = aa_get_buffer(false);
 	if (!buffer) {
 		error = -ENOMEM;
 		goto out;
 	}
 	if (dev_path) {
-		dev_buffer = aa_get_buffer();
+		dev_buffer = aa_get_buffer(false);
 		if (!dev_buffer) {
 			error = -ENOMEM;
 			goto out;
@@ -624,7 +624,7 @@ int aa_umount(struct aa_label *label, struct vfsmount *mnt, int flags)
 	AA_BUG(!label);
 	AA_BUG(!mnt);
 
-	buffer = aa_get_buffer();
+	buffer = aa_get_buffer(false);
 	if (!buffer)
 		return -ENOMEM;
 
@@ -703,8 +703,8 @@ int aa_pivotroot(struct aa_label *label, const struct path *old_path,
 	AA_BUG(!old_path);
 	AA_BUG(!new_path);
 
-	old_buffer = aa_get_buffer();
-	new_buffer = aa_get_buffer();
+	old_buffer = aa_get_buffer(false);
+	new_buffer = aa_get_buffer(false);
 	error = -ENOMEM;
 	if (!old_buffer || !new_buffer)
 		goto out;