The sysctl knob allows users with SYS_ADMIN capability to
taint the kernel with any arbitrary value, but this might
produce an invalid flags bitset being committed to tainted_mask.
This patch introduces a simple way for proc_taint() to ignore
any eventual invalid bit coming from the user input before
committing those bits to the kernel tainted_mask.
Signed-off-by: Rafael Aquini <[email protected]>
---
include/linux/kernel.h | 2 ++
kernel/sysctl.c | 14 +++++++++++++-
2 files changed, 15 insertions(+), 1 deletion(-)
diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index 9b7a8d74a9d6..e8c22a9bbc95 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -597,6 +597,8 @@ extern enum system_states {
#define TAINT_RANDSTRUCT 17
#define TAINT_FLAGS_COUNT 18
+#define TAINT_FLAGS_MAX ((1UL << TAINT_FLAGS_COUNT) - 1)
+
struct taint_flag {
char c_true; /* character printed when tainted */
char c_false; /* character printed when not tainted */
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 8a176d8727a3..fb2d693fc08c 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -2623,11 +2623,23 @@ static int proc_taint(struct ctl_table *table, int write,
return err;
if (write) {
+ int i;
+
+ /*
+ * Ignore user input that would cause the loop below
+ * to commit arbitrary and out of valid range TAINT flags.
+ */
+ if (tmptaint > TAINT_FLAGS_MAX) {
+ tmptaint &= TAINT_FLAGS_MAX;
+ pr_warn_once("%s: out-of-range taint input ignored."
+ " tainted_mask adjusted to 0x%lx\n",
+ __func__, tmptaint);
+ }
+
/*
* Poor man's atomic or. Not worth adding a primitive
* to everyone's atomic.h for this
*/
- int i;
for (i = 0; i < BITS_PER_LONG && tmptaint >> i; i++) {
if ((tmptaint >> i) & 1)
add_taint(i, LOCKDEP_STILL_OK);
--
2.25.4
On Tue, 12 May 2020 13:46:53 -0400 Rafael Aquini <[email protected]> wrote:
> The sysctl knob
/proc/sys/kernel/tainted, yes?
> allows users with SYS_ADMIN capability to
> taint the kernel with any arbitrary value, but this might
> produce an invalid flags bitset being committed to tainted_mask.
>
> This patch introduces a simple way for proc_taint() to ignore
> any eventual invalid bit coming from the user input before
> committing those bits to the kernel tainted_mask.
>
> ...
>
> --- a/include/linux/kernel.h
> +++ b/include/linux/kernel.h
> @@ -597,6 +597,8 @@ extern enum system_states {
> #define TAINT_RANDSTRUCT 17
> #define TAINT_FLAGS_COUNT 18
>
> +#define TAINT_FLAGS_MAX ((1UL << TAINT_FLAGS_COUNT) - 1)
> +
> struct taint_flag {
> char c_true; /* character printed when tainted */
> char c_false; /* character printed when not tainted */
> diff --git a/kernel/sysctl.c b/kernel/sysctl.c
> index 8a176d8727a3..fb2d693fc08c 100644
> --- a/kernel/sysctl.c
> +++ b/kernel/sysctl.c
> @@ -2623,11 +2623,23 @@ static int proc_taint(struct ctl_table *table, int write,
> return err;
>
> if (write) {
> + int i;
> +
> + /*
> + * Ignore user input that would cause the loop below
> + * to commit arbitrary and out of valid range TAINT flags.
> + */
> + if (tmptaint > TAINT_FLAGS_MAX) {
> + tmptaint &= TAINT_FLAGS_MAX;
> + pr_warn_once("%s: out-of-range taint input ignored."
> + " tainted_mask adjusted to 0x%lx\n",
> + __func__, tmptaint);
> + }
> +
> /*
> * Poor man's atomic or. Not worth adding a primitive
> * to everyone's atomic.h for this
> */
> - int i;
> for (i = 0; i < BITS_PER_LONG && tmptaint >> i; i++) {
Could simply replace BITS_PER_LONG with TAINT_FLAGS_COUNT here?
(That "&& tmptaint >> i" seems a rather silly optimization?)
> if ((tmptaint >> i) & 1)
> add_taint(i, LOCKDEP_STILL_OK);
In fact the whole thing could be simplified down to
for (i = 1; i <= TAINT_FLAGS_COUNT; i <<= 1)
if (i & tmptaint)
add_taint(...)
and silently drop out-of-range bits?
On Tue, May 12, 2020 at 01:53:26PM -0700, Andrew Morton wrote:
> On Tue, 12 May 2020 13:46:53 -0400 Rafael Aquini <[email protected]> wrote:
>
> > The sysctl knob
>
> /proc/sys/kernel/tainted, yes?
>
> > allows users with SYS_ADMIN capability to
> > taint the kernel with any arbitrary value, but this might
> > produce an invalid flags bitset being committed to tainted_mask.
> >
> > This patch introduces a simple way for proc_taint() to ignore
> > any eventual invalid bit coming from the user input before
> > committing those bits to the kernel tainted_mask.
> >
> > ...
> >
> > --- a/include/linux/kernel.h
> > +++ b/include/linux/kernel.h
> > @@ -597,6 +597,8 @@ extern enum system_states {
> > #define TAINT_RANDSTRUCT 17
> > #define TAINT_FLAGS_COUNT 18
> >
> > +#define TAINT_FLAGS_MAX ((1UL << TAINT_FLAGS_COUNT) - 1)
> > +
> > struct taint_flag {
> > char c_true; /* character printed when tainted */
> > char c_false; /* character printed when not tainted */
> > diff --git a/kernel/sysctl.c b/kernel/sysctl.c
> > index 8a176d8727a3..fb2d693fc08c 100644
> > --- a/kernel/sysctl.c
> > +++ b/kernel/sysctl.c
> > @@ -2623,11 +2623,23 @@ static int proc_taint(struct ctl_table *table, int write,
> > return err;
> >
> > if (write) {
> > + int i;
> > +
> > + /*
> > + * Ignore user input that would cause the loop below
> > + * to commit arbitrary and out of valid range TAINT flags.
> > + */
> > + if (tmptaint > TAINT_FLAGS_MAX) {
> > + tmptaint &= TAINT_FLAGS_MAX;
> > + pr_warn_once("%s: out-of-range taint input ignored."
> > + " tainted_mask adjusted to 0x%lx\n",
> > + __func__, tmptaint);
> > + }
> > +
> > /*
> > * Poor man's atomic or. Not worth adding a primitive
> > * to everyone's atomic.h for this
> > */
> > - int i;
> > for (i = 0; i < BITS_PER_LONG && tmptaint >> i; i++) {
>
> Could simply replace BITS_PER_LONG with TAINT_FLAGS_COUNT here?
>
> (That "&& tmptaint >> i" seems a rather silly optimization?)
>
> > if ((tmptaint >> i) & 1)
> > add_taint(i, LOCKDEP_STILL_OK);
>
> In fact the whole thing could be simplified down to
>
> for (i = 1; i <= TAINT_FLAGS_COUNT; i <<= 1)
> if (i & tmptaint)
> add_taint(...)
>
> and silently drop out-of-range bits?
>
Sure!
-- Rafael
On Tue, May 12, 2020 at 01:46:53PM -0400, Rafael Aquini wrote:
> The sysctl knob allows users with SYS_ADMIN capability to
> taint the kernel with any arbitrary value, but this might
> produce an invalid flags bitset being committed to tainted_mask.
>
> This patch introduces a simple way for proc_taint() to ignore
> any eventual invalid bit coming from the user input before
> committing those bits to the kernel tainted_mask.
>
> Signed-off-by: Rafael Aquini <[email protected]>
Acked-by: Luis Chamberlain <[email protected]>
Luis