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[2001:8b0:1d0::2]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-37d32ea1d98sm1490936f8f.68.2024.10.08.09.47.10 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 08 Oct 2024 09:47:10 -0700 (PDT) From: Peter Maydell To: qemu-devel@nongnu.org Cc: qemu-block@nongnu.org, Kevin Wolf , Hanna Reitz , Stefan Weil Subject: [PATCH v2 2/4] block/ssh.c: Don't double-check that characters are hex digits Date: Tue, 8 Oct 2024 17:47:06 +0100 Message-Id: <20241008164708.2966400-3-peter.maydell@linaro.org> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20241008164708.2966400-1-peter.maydell@linaro.org> References: <20241008164708.2966400-1-peter.maydell@linaro.org> MIME-Version: 1.0 Received-SPF: pass client-ip=2a00:1450:4864:20::42c; envelope-from=peter.maydell@linaro.org; helo=mail-wr1-x42c.google.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org Sender: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org In compare_fingerprint() we effectively check whether the characters in the fingerprint are valid hex digits twice: first we do so with qemu_isxdigit(), but then the hex2decimal() function also has a code path where it effectively detects an invalid digit and returns -1. This causes Coverity to complain because it thinks that we might use that -1 value in an expression where it would be an integer overflow. Avoid the double-check of hex digit validity by testing the return values from hex2decimal() rather than doing separate calls to qemu_isxdigit(). Since this means we now use the illegal-character return value from hex2decimal(), rewrite it from "-1" to "UINT_MAX", which has the same effect since the return type is "unsigned" but looks less confusing at the callsites when we detect it with "c0 > 0xf". Resolves: Coverity CID 1547813 Signed-off-by: Peter Maydell Reviewed-by: Kevin Wolf Reviewed-by: Richard Henderson --- v1->v2: make hex2decimal() return UINT_MAX, not -1 --- block/ssh.c | 12 +++++++----- 1 file changed, 7 insertions(+), 5 deletions(-) diff --git a/block/ssh.c b/block/ssh.c index 871e1d47534..9f8140bcb68 100644 --- a/block/ssh.c +++ b/block/ssh.c @@ -364,7 +364,7 @@ static unsigned hex2decimal(char ch) return 10 + (ch - 'A'); } - return -1; + return UINT_MAX; } /* Compare the binary fingerprint (hash of host key) with the @@ -376,13 +376,15 @@ static int compare_fingerprint(const unsigned char *fingerprint, size_t len, unsigned c; while (len > 0) { + unsigned c0, c1; while (*host_key_check == ':') host_key_check++; - if (!qemu_isxdigit(host_key_check[0]) || - !qemu_isxdigit(host_key_check[1])) + c0 = hex2decimal(host_key_check[0]); + c1 = hex2decimal(host_key_check[1]); + if (c0 > 0xf || c1 > 0xf) { return 1; - c = hex2decimal(host_key_check[0]) * 16 + - hex2decimal(host_key_check[1]); + } + c = c0 * 16 + c1; if (c - *fingerprint != 0) return c - *fingerprint; fingerprint++;