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@xxxxxxxxxx>
---
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
