> -----Original Message----- > From: Intel-wired-lan <[email protected]> On Behalf Of Jacob > Keller > Sent: 23 July 2025 05:45 > To: Intel Wired LAN <[email protected]>; [email protected] > Cc: Simon Horman <[email protected]>; Nguyen, Anthony L > <[email protected]>; Kunwu Chan <[email protected]>; Wang Haoran > <[email protected]>; Amir Mohammad Jahangirzad > <[email protected]>; Keller, Jacob E <[email protected]> > Subject: [Intel-wired-lan] [PATCH] i40e: remove read access to debugfs files > > The 'command' and 'netdev_ops' debugfs files are a legacy debugging interface > supported by the i40e driver since its early days by commit 02e9c290814c > ("i40e: debugfs interface"). > > Both of these debugfs files provide a read handler which is mostly useless, > and which is implemented with questionable logic. They both use a static 256 byte buffer which is initialized to the empty string. In the case of the 'command' file this buffer is literally never used and simply wastes space. In the case of the 'netdev_ops' file, the last command written is saved here. > > On read, the files contents are presented as the name of the device followed > by a colon and then the contents of their respective static buffer. For > 'command' this will always be "<device>: ". For 'netdev_ops', this will be > "<device>: <last command written>". But note the buffer is shared between all > devices operated by this module. At best, it is mostly meaningless > information, and at worse it could be accessed simultaneously as there > doesn't appear to be any locking mechanism. > > We have also recently received multiple reports for both read functions about > their use of snprintf and potential overflow that could result in reading > arbitrary kernel memory. For the 'command' file, this is definitely > impossible, since the static buffer is always zero and never written to. > For the 'netdev_ops' file, it does appear to be possible, if the user > carefully crafts the command input, it will be copied into the buffer, which > could be large enough to cause snprintf to truncate, which then causes the > copy_to_user to read beyond the length of the buffer allocated by kzalloc. > > A minimal fix would be to replace snprintf() with scnprintf() which would cap > the return to the number of bytes written, preventing an overflow. A more > involved fix would be to drop the mostly useless static buffers, saving 512 > bytes and modifying the read functions to stop needing those as input. > > Instead, lets just completely drop the read access to these files. These are > debug interfaces exposed as part of debugfs, and I don't believe that > dropping read access will break any script, as the provided output is pretty > useless. You can find the netdev name through other more standard interfaces, > and the 'netdev_ops' interface can easily result in garbage if you issue > simultaneous writes to multiple devices at once. > > In order to properly remove the i40e_dbg_netdev_ops_buf, we need to refactor > its write function to avoid using the static buffer. Instead, use the same > logic as the i40e_dbg_command_write, with an allocated buffer. > Update the code to use this instead of the static buffer, and ensure we free > the buffer on exit. This fixes simultaneous writes to 'netdev_ops' on > multiple devices, and allows us to remove the now unused static buffer along > with removing the read access. > > Reported-by: Kunwu Chan <[email protected]> > Closes: > https://lore.kernel.org/intel-wired-lan/[email protected]/ > Reported-by: Wang Haoran <[email protected]> > Closes: > https://lore.kernel.org/all/CANZ3JQRRiOdtfQJoP9QM=6LS1Jto8PGBGw6y7-TL=bcnzhq...@mail.gmail.com/ > Reported-by: Amir Mohammad Jahangirzad <[email protected]> > Closes: > https://lore.kernel.org/all/[email protected]/ > Signed-off-by: Jacob Keller <[email protected]> > --- > I found several reports of the issues with these read functions going at > least as far back as 2023, with suggestions to remove the read access even > back then. None of the fixes got accepted or applied, but neither did Intel > follow up with removing the interfaces. Its time to just drop the read access > altogether. > --- > drivers/net/ethernet/intel/i40e/i40e_debugfs.c | 123 ++++--------------------- > 1 file changed, 19 insertions(+), 104 deletions(-) >
Tested-by: Rinitha S <[email protected]> (A Contingent worker at Intel)
