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    Subject[PATCH 6.0 729/862] drm: Use size_t type for len variable in drm_copy_field()
    Date
    From: Javier Martinez Canillas <javierm@redhat.com>

    [ Upstream commit 94dc3471d1b2b58b3728558d0e3f264e9ce6ff59 ]

    The strlen() function returns a size_t which is an unsigned int on 32-bit
    arches and an unsigned long on 64-bit arches. But in the drm_copy_field()
    function, the strlen() return value is assigned to an 'int len' variable.

    Later, the len variable is passed as copy_from_user() third argument that
    is an unsigned long parameter as well.

    In theory, this can lead to an integer overflow via type conversion. Since
    the assignment happens to a signed int lvalue instead of a size_t lvalue.

    In practice though, that's unlikely since the values copied are set by DRM
    drivers and not controlled by userspace. But using a size_t for len is the
    correct thing to do anyways.

    Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
    Tested-by: Peter Robinson <pbrobinson@gmail.com>
    Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
    Link: https://patchwork.freedesktop.org/patch/msgid/20220705100215.572498-2-javierm@redhat.com
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    drivers/gpu/drm/drm_ioctl.c | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    diff --git a/drivers/gpu/drm/drm_ioctl.c b/drivers/gpu/drm/drm_ioctl.c
    index 8faad23dc1d8..e1b9a03e619c 100644
    --- a/drivers/gpu/drm/drm_ioctl.c
    +++ b/drivers/gpu/drm/drm_ioctl.c
    @@ -472,7 +472,7 @@ EXPORT_SYMBOL(drm_invalid_op);
    */
    static int drm_copy_field(char __user *buf, size_t *buf_len, const char *value)
    {
    - int len;
    + size_t len;

    /* don't overflow userbuf */
    len = strlen(value);
    --
    2.35.1


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