dmidecode: Use read_file() to read the DMI table from sysfs

We shouldn't use mem_chunk() to read the DMI table from sysfs. This will fail for SMBIOS v3 implementations which specify a maximum length for the table rather than its exact length. The kernel will trim the table to the actual length, so the DMI file will be shorter than the length announced in entry point. read_file() fits the bill in this case, as it deals with end of file nicely. This also helps with corrupted DMI tables, as the kernel will not export the part of the table that it wasn't able to parse, effectively trimming it. This fixes bug #46176: https://savannah.nongnu.org/bugs/?46176 Unexpected end of file error
somarasa · Nov 2, 2015 · 3640552 · 3640552
1 parent de9a74e
commit 3640552
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diff --git a/CHANGELOG b/CHANGELOG
@@ -2,6 +2,9 @@
 
 	* dmidecode.c, util.c, util.h: Let read_file return the actual data
 	  size.
+	* dmidecode.c: Use read_file to read the DMI table from sysfs.
+	  This fixes Savannah bug #46176:
+	  https://savannah.nongnu.org/bugs/?46176
 
 2015-10-21  Xie XiuQi  <xiexiuqi@huawei.com>
 

diff --git a/dmidecode.c b/dmidecode.c
@@ -4524,16 +4524,29 @@ static void dmi_table(off_t base, u32 len, u16 num, u16 ver, const char *devmem,
 		printf("\n");
 	}
 
-	/*
-	 * When we are reading the DMI table from sysfs, we want to print
-	 * the address of the table (done above), but the offset of the
-	 * data in the file is 0.  When reading from /dev/mem, the offset
-	 * in the file is the address.
-	 */
 	if (flags & FLAG_NO_FILE_OFFSET)
-		base = 0;
+	{
+		/*
+		 * When reading from sysfs, the file may be shorter than
+		 * announced. For SMBIOS v3 this is expcted, as we only know
+		 * the maximum table size, not the actual table size. For older
+		 * implementations (and for SMBIOS v3 too), this would be the
+		 * result of the kernel truncating the table on parse error.
+		 */
+		size_t size = len;
+		buf = read_file(&size, devmem);
+		if (!(opt.flags & FLAG_QUIET) && num && size != (size_t)len)
+		{
+			printf("Wrong DMI structures length: %u bytes "
+				"announced, only %lu bytes available.\n",
+				len, (unsigned long)size);
+		}
+		len = size;
+	}
+	else
+		buf = mem_chunk(base, len, devmem);
 
-	if ((buf = mem_chunk(base, len, devmem)) == NULL)
+	if (buf == NULL)
 	{
 		fprintf(stderr, "Table is unreachable, sorry."
 #ifndef USE_MMAP