[PATCH 4.19 49/58] module: Do not expose section addresses to non-CAP_SYSLOG

[Greg Kroah-Hartman]

From: Kees Cook <keesc...@chromium.org>

commit b25a7c5af9051850d4f3d93ca500056ab6ec724b upstream.

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.czarn...@trailofbits.com>
Fixes: be71eda5383f ("module: Fix display of wrong module .text address")
Cc: sta...@vger.kernel.org
Tested-by: Jessica Yu <j...@kernel.org>
Acked-by: Jessica Yu <j...@kernel.org>
Signed-off-by: Kees Cook <keesc...@chromium.org>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>

---
 kernel/module.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

--- a/kernel/module.c
+++ b/kernel/module.c
@@ -1471,8 +1471,8 @@ static ssize_t module_sect_read(struct f
        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)
@@ -4260,7 +4260,7 @@ static int modules_open(struct inode *in
 
        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;