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kallsyms: Refactor kallsyms_show_value() to take cred

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commit 160251842cd35a75edfb0a1d76afa3eb674ff40a upstream.

In order to perform future tests against the cred saved during open(),
switch kallsyms_show_value() to operate on a cred, and have all current
callers pass current_cred(). This makes it very obvious where callers
are checking the wrong credential in their "read" contexts. These will
be fixed in the coming patches.

Additionally switch return value to bool, since it is always used as a
direct permission check, not a 0-on-success, negative-on-error style
function return.

Cc: stable@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Kees Cook 2020-07-02 11:49:23 -07:00 • committed by Greg Kroah-Hartman
commit 2a6c8d3d0d
5 changed files with 18 additions and 12 deletions
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17
kernel/kallsyms.c
View file

@ -645,19 +645,20 @@ static inline int kallsyms_for_perf(void)
* Otherwise, require CAP_SYSLOG (assuming kptr_restrict isn't set to
* block even that).
*/
int kallsyms_show_value(void)
bool kallsyms_show_value(const struct cred *cred)
{
switch (kptr_restrict) {
case 0:
if (kallsyms_for_perf())
return 1;
return true;
/* fallthrough */
case 1:
if (has_capability_noaudit(current, CAP_SYSLOG))
return 1;
if (security_capable(cred, &init_user_ns, CAP_SYSLOG,
CAP_OPT_NOAUDIT) == 0)
return true;
/* fallthrough */
default:
return 0;
return false;
}
}
@ -674,7 +675,11 @@ static int kallsyms_open(struct inode *inode, struct file *file)
return -ENOMEM;
reset_iter(iter, 0);
iter->show_value = kallsyms_show_value();
/*
* Instead of checking this on every s_show() call, cache
* the result here at open time.
*/
iter->show_value = kallsyms_show_value(file->f_cred);
return 0;
}

4
kernel/kprobes.c
View file

@ -2362,7 +2362,7 @@ static void report_probe(struct seq_file *pi, struct kprobe *p,
else
kprobe_type = "k";
if (!kallsyms_show_value())
if (!kallsyms_show_value(current_cred()))
addr = NULL;
if (sym)
@ -2463,7 +2463,7 @@ static int kprobe_blacklist_seq_show(struct seq_file *m, void *v)
* If /proc/kallsyms is not showing kernel address, we won't
* show them here either.
*/
if (!kallsyms_show_value())
if (!kallsyms_show_value(current_cred()))
seq_printf(m, "0x%px-0x%px\t%ps\n", NULL, NULL,
(void *)ent->start_addr);
else

2
kernel/module.c
View file

@ -4391,7 +4391,7 @@ static int modules_open(struct inode *inode, struct file *file)
if (!err) {
struct seq_file *m = file->private_data;
m->private = kallsyms_show_value() ? NULL : (void *)8ul;
m->private = kallsyms_show_value(current_cred()) ? NULL : (void *)8ul;
}
return err;