| Message ID | 20200512174653.770506-1-aquini@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | kernel: sysctl: ignore out-of-range taint bits introduced via kernel.tainted | expand |
On Tue, 12 May 2020 13:46:53 -0400 Rafael Aquini <aquini@redhat.com> 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 <aquini@redhat.com> 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 <aquini@redhat.com> Acked-by: Luis Chamberlain <mcgrof@kernel.org> Luis
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);
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 <aquini@redhat.com> --- include/linux/kernel.h | 2 ++ kernel/sysctl.c | 14 +++++++++++++- 2 files changed, 15 insertions(+), 1 deletion(-)