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[PATCH 0/2] pstore: Make default pstorefs root dir perms 0750

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  [PATCH 0/2] pstore: Make default pstorefs root dir perms 0750 Kees Cook <keescook@chromium.org> - 2017-08-10 22:40 +0200
    [PATCH 2/2] Revert "pstore: Honor dmesg_restrict sysctl on dmesg dumps" Kees Cook <keescook@chromium.org> - 2017-08-10 22:40 +0200
    [PATCH 1/2] pstore: Make default pstorefs root dir perms 0750 Kees Cook <keescook@chromium.org> - 2017-08-10 22:40 +0200

#1709009 — [PATCH 0/2] pstore: Make default pstorefs root dir perms 0750

Nick Kralevich pointed out that it was rather problematic to check
capabilities when reading some pstore files. Instead, opt for a more
configurable DAC approach, but retain the general protection by making the
pstorefs root directory mode 0750. It was 0755, but most crash-handlers
will also be performing unlink operations (which DAC would require a
root uid perm for already), so this shouldn't affect anyone, but rather
make permissions more flexible.

-Kees

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#1709011 — [PATCH 2/2] Revert "pstore: Honor dmesg_restrict sysctl on dmesg dumps"

This reverts commit 68c4a4f8abc60c9440ede9cd123d48b78325f7a3, with
various conflict clean-ups.

With the default root directory mode set to 0750 now, the capability
check was redundant.

Suggested-by: Nick Kralevich <nnk@google.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
---
 fs/pstore/inode.c      | 22 ----------------------
 include/linux/syslog.h |  9 ---------
 kernel/printk/printk.c |  3 +--
 3 files changed, 1 insertion(+), 33 deletions(-)

diff --git a/fs/pstore/inode.c b/fs/pstore/inode.c
index f1e88b695090..d814723fb27d 100644
--- a/fs/pstore/inode.c
+++ b/fs/pstore/inode.c
@@ -36,7 +36,6 @@
 #include <linux/slab.h>
 #include <linux/spinlock.h>
 #include <linux/uaccess.h>
-#include <linux/syslog.h>
 
 #include "internal.h"
 
@@ -132,18 +131,6 @@ 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->record->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)
 {
@@ -163,10 +150,6 @@ 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->record->type == PSTORE_TYPE_FTRACE)
 		sops = &pstore_ftrace_seq_ops;
 
@@ -204,11 +187,6 @@ static int pstore_unlink(struct inode *dir, struct dentry *dentry)
 {
 	struct pstore_private *p = d_inode(dentry)->i_private;
 	struct pstore_record *record = p->record;
-	int err;
-
-	err = pstore_check_syslog_permissions(p);
-	if (err)
-		return err;
 
 	if (!record->psi->erase)
 		return -EPERM;
diff --git a/include/linux/syslog.h b/include/linux/syslog.h
index c3a7f0cc3a27..e1c3632f4e81 100644
--- a/include/linux/syslog.h
+++ b/include/linux/syslog.h
@@ -49,13 +49,4 @@
 
 int do_syslog(int type, char __user *buf, int count, int source);
 
-#ifdef CONFIG_PRINTK
-int check_syslog_permissions(int type, int source);
-#else
-static inline int check_syslog_permissions(int type, int source)
-{
-	return 0;
-}
-#endif
-
 #endif /* _LINUX_SYSLOG_H */
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index fc47863f629c..97bda7b0655b 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -649,7 +649,7 @@ static int syslog_action_restricted(int type)
 	       type != SYSLOG_ACTION_SIZE_BUFFER;
 }
 
-int check_syslog_permissions(int type, int source)
+static int check_syslog_permissions(int type, int source)
 {
 	/*
 	 * If this is from /proc/kmsg and we've already opened it, then we've
@@ -677,7 +677,6 @@ int check_syslog_permissions(int type, int source)
 ok:
 	return security_syslog(type);
 }
-EXPORT_SYMBOL_GPL(check_syslog_permissions);
 
 static void append_char(char **pp, char *e, char c)
 {
-- 
2.7.4

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#1709013 — [PATCH 1/2] pstore: Make default pstorefs root dir perms 0750

Currently only DMESG and CONSOLE record types are protected, and it isn't
obvious that they are using a capability check. Instead switch to explicit
root directory mode of 0750 to keep files private by default.  This will
allow the removal of the capability check, which was non-obvious and
forces a process to have possibly too much privilege when simple post-boot
chgrp for readers would be possible without it.

Signed-off-by: Kees Cook <keescook@chromium.org>
---
 fs/pstore/inode.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/pstore/inode.c b/fs/pstore/inode.c
index fefd22611cf6..f1e88b695090 100644
--- a/fs/pstore/inode.c
+++ b/fs/pstore/inode.c
@@ -471,7 +471,7 @@ static int pstore_fill_super(struct super_block *sb, void *data, int silent)
 
 	inode = pstore_get_inode(sb);
 	if (inode) {
-		inode->i_mode = S_IFDIR | 0755;
+		inode->i_mode = S_IFDIR | 0750;
 		inode->i_op = &pstore_dir_inode_operations;
 		inode->i_fop = &simple_dir_operations;
 		inc_nlink(inode);
-- 
2.7.4

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