On Tue, Apr 13, 2021 at 05:02:40PM +0800, Jisheng Zhang wrote:
> I met below error during boot with i915 builtin if pass
> "i915.mitigations=off":
> [ 0.015589] Booting kernel: `off' invalid for parameter `i915.mitigations'
>
> The reason is slab subsystem isn't ready at that time, so kstrdup()
> returns NULL. Fix this issue by using stack var instead of kstrdup().
>
> Fixes: 984cadea032b ("drm/i915: Allow the sysadmin to override security mitigations")
> Signed-off-by: Jisheng Zhang <Jisheng.Zhang@xxxxxxxxxxxxx>
> ---
> drivers/gpu/drm/i915/i915_mitigations.c | 7 ++-----
> 1 file changed, 2 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_mitigations.c b/drivers/gpu/drm/i915/i915_mitigations.c
> index 84f12598d145..7dadf41064e0 100644
> --- a/drivers/gpu/drm/i915/i915_mitigations.c
> +++ b/drivers/gpu/drm/i915/i915_mitigations.c
> @@ -29,15 +29,13 @@ bool i915_mitigate_clear_residuals(void)
> static int mitigations_set(const char *val, const struct kernel_param *kp)
> {
> unsigned long new = ~0UL;
> - char *str, *sep, *tok;
> + char str[64], *sep, *tok;
> bool first = true;
> int err = 0;
>
> BUILD_BUG_ON(ARRAY_SIZE(names) >= BITS_PER_TYPE(mitigations));
>
> - str = kstrdup(val, GFP_KERNEL);
> - if (!str)
> - return -ENOMEM;
> + strncpy(str, val, sizeof(str) - 1);
I don't think strncpy() guarantees that the string is properly
terminated.
Also commit b1b6bed3b503 ("usb: core: fix quirks_param_set() writing to
a const pointer") looks broken as well given your findings, and
arch/um/drivers/virtio_uml.c seems to suffer from this as well.
kernel/params.c itself seems to have some slab_is_available() magic
around kmalloc().
I used the following cocci snippet to find these:
@find@
identifier O, F;
position PS;
@@
struct kernel_param_ops O = {
...,
.set = F@PS
,...
};
@alloc@
identifier ALLOC =~ "^k.*(alloc|dup)";
identifier find.F;
position PA;
@@
F(...) {
<+...
ALLOC@PA(...)
...+>
}
@script:python depends on alloc@
ps << find.PS;
pa << alloc.PA;
@@
coccilib.report.print_report(ps[0], "struct")
coccilib.report.print_report(pa[0], "alloc")
That could of course miss a bunch more if they allocate
via some other function I didn't consider.
--
Ville Syrjälä
Intel
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