module: Do not expose section addresses to non-CAP_SYSLOG

The printing of section addresses in /sys/module/*/sections/* was not using the correct credentials to evaluate visibility. Before: # cat /sys/module/*/sections/.*text 0xffffffffc0458000 ... # capsh --drop=CAP_SYSLOG -- -c "cat /sys/module/*/sections/.*text" 0xffffffffc0458000 ... After: # cat /sys/module/*/sections/*.text 0xffffffffc0458000 ... # capsh --drop=CAP_SYSLOG -- -c "cat /sys/module/*/sections/.*text" 0x0000000000000000 ... Additionally replaces the existing (safe) /proc/modules check with file->f_cred for consistency. Reported-by: Dominik Czarnota <[email protected]> Fixes: be71eda ("module: Fix display of wrong module .text address") Cc: [email protected] Tested-by: Jessica Yu <[email protected]> Acked-by: Jessica Yu <[email protected]> Signed-off-by: Kees Cook <[email protected]>
chewitt · Jul 8, 2020 · b25a7c5 · b25a7c5
1 parent ed66f99
commit b25a7c5
Showing 1 changed file with 3 additions and 3 deletions.
diff --git a/kernel/module.c b/kernel/module.c
@@ -1530,8 +1530,8 @@ static ssize_t module_sect_read(struct file *file, struct kobject *kobj,
 	if (pos != 0)
 		return -EINVAL;
 
-	return sprintf(buf, "0x%px\n", kptr_restrict < 2 ?
-		       (void *)sattr->address : NULL);
+	return sprintf(buf, "0x%px\n",
+		       kallsyms_show_value(file->f_cred) ? (void *)sattr->address : NULL);
 }
 
 static void free_sect_attrs(struct module_sect_attrs *sect_attrs)
@@ -4380,7 +4380,7 @@ static int modules_open(struct inode *inode, struct file *file)
 
 	if (!err) {
 		struct seq_file *m = file->private_data;
-		m->private = kallsyms_show_value(current_cred()) ? NULL : (void *)8ul;
+		m->private = kallsyms_show_value(file->f_cred) ? NULL : (void *)8ul;
 	}
 
 	return err;