Re: [RFC PATCH v1 1/2] maccess: fix writing offset in case of fault in strncpy_from_kernel_nofault()

[Andrew Morton]

On Tue,  8 Nov 2022 20:52:06 +0100 Francis Laniel <flaniel@xxxxxxxxxxxxxxxxxxx> wrote:

> From: Alban Crequy <albancrequy@xxxxxxxxxxxxx>
> 
> If a page fault occurs while copying the first byte, this function resets one
> byte before dst.
> As a consequence, an address could be modified and leaded to kernel crashes if
> case the modified address was accessed later.
> 
> Signed-off-by: Alban Crequy <albancrequy@xxxxxxxxxxxxx>
> Tested-by: Francis Laniel <flaniel@xxxxxxxxxxxxxxxxxxx>

Reviewed-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>

Please merge via the bpf tree.

This looks potentially nasty.  Fortunately only tracing code uses it,
but I'm thinking it should have cc:stable and a Fixes:?