soc: qcom: mdt_loader: Deal with zero e_shentsize

Firmware that doesn't provide section headers leave both e_shentsize and
e_shnum 0, which obvious isn't compatible with the newly introduced
stricter checks.

Make the section-related checks conditional on either of these values
being non-zero.

Fixes: 9f9967f ("soc: qcom: mdt_loader: Ensure we don't read past the ELF header")
Reported-by: Val Packett <val@packett.cool>
Closes: https://lore.kernel.org/all/ece307c3-7d65-440f-babd-88cf9705b908@packett.cool/
Reported-by: Neil Armstrong <neil.armstrong@linaro.org>
Closes: https://lore.kernel.org/all/aec9cd03-6fc2-4dc8-b937-8b7cf7bf4128@linaro.org/
Signed-off-by: Bjorn Andersson <bjorn.andersson@oss.qualcomm.com>
Fixes: 9f35ab0 ("soc: qcom: mdt_loader: Fix error return values in mdt_header_valid()")
Tested-by: Neil Armstrong <neil.armstrong@linaro.org> # on SM8650-QRD
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20250730-mdt-loader-shentsize-zero-v1-1-04f43186229c@oss.qualcomm.com
Signed-off-by: Bjorn Andersson <andersson@kernel.org>

Author: quic-bjorande

drivers/soc/qcom/mdt_loader.c

@@ -39,12 +39,14 @@ static bool mdt_header_valid(const struct firmware *fw)
 	if (phend > fw->size)
 		return false;
 
-	if (ehdr->e_shentsize != sizeof(struct elf32_shdr))
-		return false;
+	if (ehdr->e_shentsize || ehdr->e_shnum) {
+		if (ehdr->e_shentsize != sizeof(struct elf32_shdr))
+			return false;
 
-	shend = size_add(size_mul(sizeof(struct elf32_shdr), ehdr->e_shnum), ehdr->e_shoff);
-	if (shend > fw->size)
-		return false;
+		shend = size_add(size_mul(sizeof(struct elf32_shdr), ehdr->e_shnum), ehdr->e_shoff);
+		if (shend > fw->size)
+			return false;
+	}
 
 	return true;
 }