Christian Lamparter <chunkeey@xxxxxxxxx> writes: > On 12/19/23 17:25, Kalle Valo wrote: >> GCC 13.2 warns: >> drivers/net/wireless/intersil/p54/fwio.c:128:34: warning: '%s' >> directive output may be truncated writing up to 39 bytes into a >> region of size 32 [-Wformat-truncation=] >> drivers/net/wireless/intersil/p54/fwio.c:128:33: note: directive argument in the range [0, 16777215] >> drivers/net/wireless/intersil/p54/fwio.c:128:33: note: directive argument in the range [0, 255] >> drivers/net/wireless/intersil/p54/fwio.c:127:17: note: 'snprintf' >> output between 7 and 52 bytes into a destination of size 32 >> The issue here is that wiphy->fw_version is 32 bytes and in theory >> the string >> we try to place there can be 39 bytes. > Puh, I've been looking into /lib/vsprintf.c. Looking at the code, it seems > that it goes like this: > > snprintf() -> vsnprintf() -> case FORMAT_TYPE_STR: -> string() -> string_nocheck(): > | [...] > | if (buf < end) > | *buf = c; > | [...] > > which dutifully checks for overruns (i.e. before writing into the buffer=wiphy->fw_version). > So, thankfully no blind memcpy/strcpy is taking place here. > Though, I don't know if this could be used for speculation attacks. > >> wiphy->fw_version is used for providing >> the firmware version to user space via ethtool, so not really important. >> fw_version in theory can be 24 bytes but in practise it's shorter, so even if >> print only 19 bytes via ethtool there should not be any practical difference. >> I did consider removing fw_var from the string altogether or making >> the maximum >> length for fw_version 19 bytes, but chose this approach as it was the least >> intrusive. >> Signed-off-by: Kalle Valo <kvalo@xxxxxxxxxx> > > |ethtool -i wlx0014a535e989 > |driver: p54usb > |version: 6.7.0-rc6-wt+ > |firmware-version: 2.13.25.0 - 5.9 > |expansion-rom-version: > |bus-info: 5-2:1.0 > |supports-statistics: yes > |supports-test: no > |supports-eeprom-access: no > |supports-register-dump: no > |supports-priv-flags: no > > (yes, this doesn't change the output of ethtool. The firmware version is indeed > much much shorter than 24 bytes for the firmwares I know of.) Thanks for checking all this. > To be honest, I would write something like: "This patch silences gcc" in the commit > message. Rather than trying to come up with a well-intended justification. But I get > why this happens. That said, I would like to see gcc envolve... And maybe then it > will add warnings that go in the other direction (i.e. it will complain that > this %.19s was unnecessary here) :D. > > Acked-by: Christian Lamparter <chunkeey@xxxxxxxxx> (Tested with Dell 1450 USB) Yeah, I get why you dislike this. But it's just that net tree more or less requires that our code is W=1 warning free and it will be soon become a mess if we have existing warnings. So having this fixed, or silenced, makes my life easier. -- https://patchwork.kernel.org/project/linux-wireless/list/ https://wireless.wiki.kernel.org/en/developers/documentation/submittingpatches
