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Subject[PATCH 5.4 089/109] module: Do not expose section addresses to non-CAP_SYSLOG
Date
From: Kees Cook <keescook@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.czarnota@trailofbits.com>
Fixes: be71eda5383f ("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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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

--- a/kernel/module.c
+++ b/kernel/module.c
@@ -1527,8 +1527,8 @@ 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)
@@ -4394,7 +4394,7 @@ 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;

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