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[217.105.56.94]) by smtp.gmail.com with ESMTPSA id 4fb4d7f45d1cf-68704a658d3sm1547636a12.17.2026.05.20.09.53.14 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 20 May 2026 09:53:16 -0700 (PDT) Message-ID: <6a0de6fc.2d57a604.3a8602.5396@mx.google.com> Date: Wed, 20 May 2026 09:53:16 -0700 (PDT) From: Alexandru Hossu To: mlombard@arkamax.eu Cc: martin.petersen@oracle.com, bvanassche@acm.org, ddiss@suse.de, target-devel@vger.kernel.org, linux-scsi@vger.kernel.org, stable@vger.kernel.org, hossu.alexandru@gmail.com Subject: Re: [PATCH v2] scsi: target: iscsi: validate CHAP_R length before base64 decode In-Reply-To: References: <20260518121811.385350-1-hossu.alexandru@gmail.com> <20260518235040.48647-1-hossu.alexandru@gmail.com> Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Wed, May 20, 2026, Maurizio Lombardi wrote: > There is something that doesn't totally convince me about this length check. > Couldn't chap_r contain those Base64 padding '=' characters that > would make strlen(chap_r) too big to pass this check? Correct. For SHA-256, a padded encoding of the 32-byte digest is 44 characters (43 data + one '='), but DIV_ROUND_UP(32 * 4, 3) = 43, so a legitimate padded response would be incorrectly rejected. v3 strips trailing '=' before the comparison: size_t r_len = strlen(chap_r); while (r_len > 0 && chap_r[r_len - 1] == '=') r_len--; if (r_len > DIV_ROUND_UP(chap->digest_size * 4, 3)) { pr_err("Malformed CHAP_R: base64 payload too long\n"); goto out; } chap_base64_decode() already handles '=' by returning early, so stripping them from the pre-check does not affect decoding. v3 below. Alexandru