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[46.142.9.55]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-48febe7e442sm13876065e9.33.2026.05.15.06.55.23 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 15 May 2026 06:55:25 -0700 (PDT) Message-ID: Date: Fri, 15 May 2026 15:55:22 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH net-next v7 2/2] net: sfp: extend SMBus support Content-Language: en-US To: Simon Horman Cc: linux@armlinux.org.uk, andrew@lunn.ch, hkallweit1@gmail.com, davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, maxime.chevallier@bootlin.com, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, bjorn@mork.no References: <20260507093301.1144740-3-jelonek.jonas@gmail.com> <20260510164741.1401430-1-horms@kernel.org> From: Jonas Jelonek In-Reply-To: <20260510164741.1401430-1-horms@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Hi, On 10.05.26 18:47, Simon Horman wrote: > From: 'Simon Horman' > > [ ... ] >> @@ -756,50 +757,110 @@ static int sfp_i2c_write(struct sfp *sfp, bool a2, u8 dev_addr, void *buf, > [ ... ] >> +static int sfp_smbus_read(struct sfp *sfp, bool a2, u8 dev_addr, void *buf, >> + size_t len) >> +{ >> + union i2c_smbus_data smbus_data; >> + u8 bus_addr = a2 ? 0x51 : 0x50; >> + size_t this_len, transferred; >> + u32 functionality; >> + u8 *data = buf; >> + int ret; >> + >> + functionality = i2c_get_functionality(sfp->i2c); >> + >> + while (len) { >> + this_len = min(len, sfp->i2c_block_size); >> + >> + if (functionality & I2C_FUNC_SMBUS_READ_I2C_BLOCK) { >> + smbus_data.block[0] = this_len; >> + ret = i2c_smbus_xfer(sfp->i2c, bus_addr, 0, >> + I2C_SMBUS_READ, dev_addr, >> + I2C_SMBUS_I2C_BLOCK_DATA, &smbus_data); >> + if (ret < 0) >> + return ret; >> + >> + memcpy(data, &smbus_data.block[1], this_len); > Can this sequence leak uninitialized kernel stack memory to the output buffer? > > When performing an I2C_SMBUS_I2C_BLOCK_DATA transfer, i2c_smbus_xfer() > updates smbus_data.block[0] with the actual number of bytes read from the > bus upon success. > > If the adapter or device returns fewer bytes than requested (a short read), > smbus_data.block[0] will be less than this_len. Because memcpy() > unconditionally copies this_len bytes, it appears it would overrun the valid > data and copy uninitialized memory from the smbus_data stack variable. > > Since the SFP EEPROM data is accessible to userspace via ethtool, could this > expose uninitialized kernel stack memory to userspace? > > Should the code verify that smbus_data.block[0] == this_len, or use > smbus_data.block[0] as the actual transferred length? Valid point, indeed uninitialized memory might be leaked here. I wouldn't use the proposed fix though. Maybe I missed it but It doesn't seem to be the contract that I2C/SMBus drivers need to update that field after read. So using that for a check seems wrong. As a fix I will just make sure no uninitialized memory is leaked. If there are other suggestions please raise your hand, otherwise I'll sned the follow-up soon. Regards, Jonas Jelonek