In the Linux kernel, the following vulnerability has been resolved:
drm/amd/display: use proper context for logging
The same as the rest of the code, get_ss_info_from_atombios() uses
calc_pll_cs->ctx->logger for logging. But calc_pll_cs->ctx is
initialized only later in calc_pll_max_vco_construct(). Therefore, any
output using DC_LOG_SYNC() leads to a NULL pointer deference in
get_ss_info_from_atombios().
According to Sashiko, the very same problem exists in
dce112_get_pix_clk_dividers() and dcn3_get_pix_clk_dividers() too.
To avoid accessing the NULL context, use clk_src->base.ctx->logger
everywhere. That context in base is initialized earlier in
dce110_clk_src_construct() and dce112_clk_src_construct(). Before
get_ss_info_from_atombios() or Sashiko's get_pix_clk_dividers functions
above are actually called. This is done by redefining DC_LOGGER to
CTX->logger.
Before:
dce110_clk_src_construct() did:
-> sets clk_src->base.ctx = ctx;
-> ss_info_from_atombios_create()
-> get_ss_info_from_atombios() <- uses calc_pll_cs->ctx # BOOM
-> calc_pll_max_vco_construct() <- sets calc_pll_cs->ctx
After:
dce110_clk_src_construct() does:
-> sets clk_src->base.ctx = ctx;
-> ss_info_from_atombios_create()
-> get_ss_info_from_atombios() <- uses clk_src->base.ctx
(cherry picked from commit 6f16fcbb0c46a87e3d9685407e906573d60104b0)