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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: be71eda538 ("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>
alistair/sunxi64-5.8
Kees Cook 2020-07-02 14:43:59 -07:00
parent ed66f991bb
commit b25a7c5af9
1 changed files with 3 additions and 3 deletions
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6
kernel/module.c
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@ -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;