From: Rafael Aquini <aquini@xxxxxxxxxx> Subject: kernel/sysctl.c: ignore out-of-range taint bits introduced via kernel.tainted Users with SYS_ADMIN capability can add arbitrary taint flags to the running kernel by writing to /proc/sys/kernel/tainted or issuing the command 'sysctl -w kernel.tainted=...'. This interface, however, is open for any integer value and this might cause an invalid set of flags being committed to the tainted_mask bitset. 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. Link: http://lkml.kernel.org/r/20200512223946.888020-1-aquini@xxxxxxxxxx Signed-off-by: Rafael Aquini <aquini@xxxxxxxxxx> Reviewed-by: Luis Chamberlain <mcgrof@xxxxxxxxxx> Cc: Kees Cook <keescook@xxxxxxxxxxxx> Cc: Iurii Zaikin <yzaikin@xxxxxxxxxx> Cc: "Theodore Ts'o" <tytso@xxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- kernel/sysctl.c | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-) --- a/kernel/sysctl.c~kernel-sysctl-ignore-out-of-range-taint-bits-introduced-via-kerneltainted +++ a/kernel/sysctl.c @@ -880,10 +880,9 @@ static int proc_taint(struct ctl_table * * Poor man's atomic or. Not worth adding a primitive * to everyone's atomic.h for this */ - for (i = 0; i < BITS_PER_LONG && tmptaint >> i; i++) { - if ((tmptaint >> i) & 1) + for (i = 0; i < TAINT_FLAGS_COUNT; i++) + if ((1UL << i) & tmptaint) add_taint(i, LOCKDEP_STILL_OK); - } } return err; _
