Commit b25a7c5a authored Jul 02, 2020 by Kees Cook

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 <dominik.czarnota@trailofbits.com>
Fixes: be71eda5 ("module: Fix display of wrong module .text address")
Cc: stable@vger.kernel.org
Tested-by: Jessica Yu <jeyu@kernel.org>
Acked-by: Jessica Yu <jeyu@kernel.org>
Signed-off-by: Kees Cook <keescook@chromium.org>

parent ed66f991

kernel/module.c

+3 −3

Original line number	Diff line number	Diff line
		@@ -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;

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