On Thu, Jun 4, 2020 at 1:18 PM Kees Cook <keescook@xxxxxxxxxxxx> wrote: > > On Thu, Jun 04, 2020 at 01:08:44PM -0700, Nick Desaulniers wrote: > > On Wed, Jun 3, 2020 at 4:32 PM Kees Cook <keescook@xxxxxxxxxxxx> wrote: > > > > > > Using uninitialized_var() is dangerous as it papers over real bugs[1] > > > (or can in the future), and suppresses unrelated compiler warnings (e.g. > > > "unused variable"). If the compiler thinks it is uninitialized, either > > > simply initialize the variable or make compiler changes. As a precursor > > > to removing[2] this[3] macro[4], just initialize this variable to NULL, > > > and make the (unreachable!) code do a conditional test. > > > > > > [1] https://lore.kernel.org/lkml/20200603174714.192027-1-glider@xxxxxxxxxx/ > > > [2] https://lore.kernel.org/lkml/CA+55aFw+Vbj0i=1TGqCR5vQkCzWJ0QxK6CernOU6eedsudAixw@xxxxxxxxxxxxxx/ > > > [3] https://lore.kernel.org/lkml/CA+55aFwgbgqhbp1fkxvRKEpzyR5J8n1vKT1VZdz9knmPuXhOeg@xxxxxxxxxxxxxx/ > > > [4] https://lore.kernel.org/lkml/CA+55aFz2500WfbKXAx8s67wrm9=yVJu65TpLgN_ybYNv0VEOKA@xxxxxxxxxxxxxx/ > > > > > > Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx> > > > --- > > > drivers/net/wireless/broadcom/b43/phy_n.c | 10 +++++++--- > > > 1 file changed, 7 insertions(+), 3 deletions(-) > > > > > > diff --git a/drivers/net/wireless/broadcom/b43/phy_n.c b/drivers/net/wireless/broadcom/b43/phy_n.c > > > index d3c001fa8eb4..88cdcea10d61 100644 > > > --- a/drivers/net/wireless/broadcom/b43/phy_n.c > > > +++ b/drivers/net/wireless/broadcom/b43/phy_n.c > > > @@ -4222,7 +4222,7 @@ static void b43_nphy_tx_gain_table_upload(struct b43_wldev *dev) > > > > The TODOs and `#if 0` in this function are concerning. It looks like > > `rf_pwr_offset_table` is only used when `phy->rev` is >=7 && < 19. > > > > Further, the loop has a case for `phy->rev >= 19` but we would have > > returned earlier if that was the case. oh, and there's an early return for `phy->rev < 3` I just noticed. > > Yeah, that's why I put the "(unreachable!)" note in the commit log. ;) I don't think that note is correct. > > > > > > u32 rfpwr_offset; > > > u8 pga_gain, pad_gain; > > > int i; > > > - const s16 *uninitialized_var(rf_pwr_offset_table); > > > + const s16 *rf_pwr_offset_table = NULL; > > > > > > table = b43_nphy_get_tx_gain_table(dev); > > > if (!table) > > > @@ -4256,9 +4256,13 @@ static void b43_nphy_tx_gain_table_upload(struct b43_wldev *dev) > > > pga_gain = (table[i] >> 24) & 0xf; > > > pad_gain = (table[i] >> 19) & 0x1f; > > > if (b43_current_band(dev->wl) == NL80211_BAND_2GHZ) > > > - rfpwr_offset = rf_pwr_offset_table[pad_gain]; > > > + rfpwr_offset = rf_pwr_offset_table > > > + ? rf_pwr_offset_table[pad_gain] > > > + : 0; > > > else > > > - rfpwr_offset = rf_pwr_offset_table[pga_gain]; > > > + rfpwr_offset = rf_pwr_offset_table > > > + ? rf_pwr_offset_table[pga_gain] > > > + : 0; > > > > > > The code is trying to check `phy->rev >= 7 && phy->rev < 19` once > > before the loop, then set `rf_pwr_offset_table`, so having another > > conditional on `rf_pwr_offset_table` in the loop is unnecessary. I'm > > ok with initializing it to `NULL`, but I'm not sure the conditional > > check is necessary. Do you get a compiler warning otherwise? > > I mean, sort of the best thing to do is just remove nearly everything > here since it's actually unreachable. But it is commented as "when This code is reachable. Consider `phy->rev >= 7 && phy->rev < 19`. If `rf_pwr_offset_table` was NULL, it would have returned early on L4246, so the checks added in this patch are unnecessary. Forgive me if there's some other control flow I'm not considering. > supported ..." etc, so I figured I'd leave it. As part of that I didn't > want to leave any chance of a NULL deref, so I added the explicit tests > just for robustness. > > *shrug* -- Thanks, ~Nick Desaulniers
