On a system that restricts access to dmesg, don't let people

side-step that by reading copies that pstore saved.
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Merge tag 'please-pull-pstore' of git://git.kernel.org/pub/scm/linux/kernel/git/aegl/linux

Pull pstore fixes from Tony Luck:
 "On a system that restricts access to dmesg, don't let people side-step
  that by reading copies that pstore saved"

* tag 'please-pull-pstore' of git://git.kernel.org/pub/scm/linux/kernel/git/aegl/linux:
  syslog: Provide stub check_syslog_permissions
  pstore: Honor dmesg_restrict sysctl on dmesg dumps
  pstore/ram: Strip ramoops header for correct decompression

fs/pstore/inode.c

@@ -36,6 +36,7 @@
 #include <linux/slab.h>
 #include <linux/spinlock.h>
 #include <linux/uaccess.h>
+#include <linux/syslog.h>
 
 #include "internal.h"
 
@@ -120,6 +121,18 @@ static const struct seq_operations pstore_ftrace_seq_ops = {
 	.show	= pstore_ftrace_seq_show,
 };
 
+static int pstore_check_syslog_permissions(struct pstore_private *ps)
+{
+	switch (ps->type) {
+	case PSTORE_TYPE_DMESG:
+	case PSTORE_TYPE_CONSOLE:
+		return check_syslog_permissions(SYSLOG_ACTION_READ_ALL,
+			SYSLOG_FROM_READER);
+	default:
+		return 0;
+	}
+}
+
 static ssize_t pstore_file_read(struct file *file, char __user *userbuf,
 						size_t count, loff_t *ppos)
 {
@@ -138,6 +151,10 @@ static int pstore_file_open(struct inode *inode, struct file *file)
 	int err;
 	const struct seq_operations *sops = NULL;
 
+	err = pstore_check_syslog_permissions(ps);
+	if (err)
+		return err;
+
 	if (ps->type == PSTORE_TYPE_FTRACE)
 		sops = &pstore_ftrace_seq_ops;
 
@@ -174,6 +191,11 @@ static const struct file_operations pstore_file_operations = {
 static int pstore_unlink(struct inode *dir, struct dentry *dentry)
 {
 	struct pstore_private *p = dentry->d_inode->i_private;
+	int err;
+
+	err = pstore_check_syslog_permissions(p);
+	if (err)
+		return err;
 
 	if (p->psi->erase)
 		p->psi->erase(p->type, p->id, p->count,

fs/pstore/ram.c

@@ -135,25 +135,27 @@ ramoops_get_next_prz(struct persistent_ram_zone *przs[], uint *c, uint max,
 	return prz;
 }
 
-static void ramoops_read_kmsg_hdr(char *buffer, struct timespec *time,
+static int ramoops_read_kmsg_hdr(char *buffer, struct timespec *time,
 				  bool *compressed)
 {
 	char data_type;
+	int header_length = 0;
 
-	if (sscanf(buffer, RAMOOPS_KERNMSG_HDR "%lu.%lu-%c\n",
-			&time->tv_sec, &time->tv_nsec, &data_type) == 3) {
+	if (sscanf(buffer, RAMOOPS_KERNMSG_HDR "%lu.%lu-%c\n%n", &time->tv_sec,
+			&time->tv_nsec, &data_type, &header_length) == 3) {
 		if (data_type == 'C')
 			*compressed = true;
 		else
 			*compressed = false;
-	} else if (sscanf(buffer, RAMOOPS_KERNMSG_HDR "%lu.%lu\n",
-			&time->tv_sec, &time->tv_nsec) == 2) {
+	} else if (sscanf(buffer, RAMOOPS_KERNMSG_HDR "%lu.%lu\n%n",
+			&time->tv_sec, &time->tv_nsec, &header_length) == 2) {
 			*compressed = false;
 	} else {
 		time->tv_sec = 0;
 		time->tv_nsec = 0;
 		*compressed = false;
 	}
+	return header_length;
 }
 
 static ssize_t ramoops_pstore_read(u64 *id, enum pstore_type_id *type,
@@ -165,6 +167,7 @@ static ssize_t ramoops_pstore_read(u64 *id, enum pstore_type_id *type,
 	ssize_t ecc_notice_size;
 	struct ramoops_context *cxt = psi->data;
 	struct persistent_ram_zone *prz;
+	int header_length;
 
 	prz = ramoops_get_next_prz(cxt->przs, &cxt->dump_read_cnt,
 				   cxt->max_dump_cnt, id, type,
@@ -178,7 +181,13 @@ static ssize_t ramoops_pstore_read(u64 *id, enum pstore_type_id *type,
 	if (!prz)
 		return 0;
 
+	if (!persistent_ram_old(prz))
+		return 0;
+
 	size = persistent_ram_old_size(prz);
+	header_length = ramoops_read_kmsg_hdr(persistent_ram_old(prz), time,
+			compressed);
+	size -= header_length;
 
 	/* ECC correction notice */
 	ecc_notice_size = persistent_ram_ecc_string(prz, NULL, 0);
@@ -187,8 +196,7 @@ static ssize_t ramoops_pstore_read(u64 *id, enum pstore_type_id *type,
 	if (*buf == NULL)
 		return -ENOMEM;
 
-	memcpy(*buf, persistent_ram_old(prz), size);
-	ramoops_read_kmsg_hdr(*buf, time, compressed);
+	memcpy(*buf, (char *)persistent_ram_old(prz) + header_length, size);
 	persistent_ram_ecc_string(prz, *buf + size, ecc_notice_size + 1);
 
 	return size + ecc_notice_size;

include/linux/syslog.h

@@ -49,4 +49,13 @@
 
 int do_syslog(int type, char __user *buf, int count, bool from_file);
 
+#ifdef CONFIG_PRINTK
+int check_syslog_permissions(int type, bool from_file);
+#else
+static inline int check_syslog_permissions(int type, bool from_file)
+{
+	return 0;
+}
+#endif
+
 #endif /* _LINUX_SYSLOG_H */

kernel/printk/printk.c

@@ -480,7 +480,7 @@ static int syslog_action_restricted(int type)
 	       type != SYSLOG_ACTION_SIZE_BUFFER;
 }
 
-static int check_syslog_permissions(int type, bool from_file)
+int check_syslog_permissions(int type, bool from_file)
 {
 	/*
 	 * If this is from /proc/kmsg and we've already opened it, then we've