Rigorously check integrity of I/O stream data

Even if fwrite() succeeds the data is not necessarily out of the clib's buffers
and writing it eventually could fail. Even if the data is flushed out (explicitly by
fflush() or implicitly by fclose()) the kernel might still hold a buffer.

Previously we have ignored this to a large extent - even in important cases
like writing the flash contents to a file. The results can be truncated
images that would brick the respective machine if written back as is (though
flashrom would not allow that due to a size mismatch). flashrom would not
indicate the problem in any output - so far we only check the return value
of fwrite() that is not conclusive.

This patch checks the return values of all related system calls like fclose()
unless we only read the file and are not really interested in output errors.
In the latter case the return value is casted to void to document this fact.
Additionally, this patch explicitly calls fflush() and fsync() (on regular files only)
to do the best we can to guarantee the read image reaches the disk safely
and at least inform the user if it did not work.

Corresponding to flashrom svn r1902.

Signed-off-by: Stefan Tauner <stefan.tauner@alumni.tuwien.ac.at>
Acked-by: Urja Rannikko <urjaman@gmail.com>

1 files changed, 45 insertions, 21 deletions

diff --git a/flashrom.c b/flashrom.c
index c9c7e31..113a05b 100644
--- a/flashrom.c
+++ b/flashrom.c
@@ -28,6 +28,7 @@
 #include <sys/stat.h>
 #endif
 #include <string.h>
+#include <unistd.h>
 #include <stdlib.h>
 #include <errno.h>
 #include <ctype.h>
@@ -1255,36 +1256,36 @@ int read_buf_from_file(unsigned char *buf, unsigned long size,
 	msg_gerr("Error: No file I/O support in libpayload\n");
 	return 1;
 #else
-	unsigned long numbytes;
-	FILE *image;
-	struct stat image_stat;
+	int ret = 0;
 
+	FILE *image;
 	if ((image = fopen(filename, "rb")) == NULL) {
 		msg_gerr("Error: opening file \"%s\" failed: %s\n", filename, strerror(errno));
 		return 1;
 	}
+
+	struct stat image_stat;
 	if (fstat(fileno(image), &image_stat) != 0) {
 		msg_gerr("Error: getting metadata of file \"%s\" failed: %s\n", filename, strerror(errno));
-		fclose(image);
-		return 1;
+		ret = 1;
+		goto out;
 	}
 	if (image_stat.st_size != size) {
 		msg_gerr("Error: Image size (%jd B) doesn't match the flash chip's size (%lu B)!\n",
 			 (intmax_t)image_stat.st_size, size);
-		fclose(image);
-		return 1;
-	}
-	numbytes = fread(buf, 1, size, image);
-	if (fclose(image)) {
-		msg_gerr("Error: closing file \"%s\" failed: %s\n", filename, strerror(errno));
-		return 1;
+		ret = 1;
+		goto out;
 	}
+
+	unsigned long numbytes = fread(buf, 1, size, image);
 	if (numbytes != size) {
 		msg_gerr("Error: Failed to read complete file. Got %ld bytes, "
 			 "wanted %ld!\n", numbytes, size);
-		return 1;
+		ret = 1;
 	}
-	return 0;
+out:
+	(void)fclose(image);
+	return ret;
 #endif
 }
 
@@ -1294,8 +1295,8 @@ int write_buf_to_file(const unsigned char *buf, unsigned long size, const char *
 	msg_gerr("Error: No file I/O support in libpayload\n");
 	return 1;
 #else
-	unsigned long numbytes;
 	FILE *image;
+	int ret = 0;
 
 	if (!filename) {
 		msg_gerr("No filename specified.\n");
@@ -1306,14 +1307,37 @@ int write_buf_to_file(const unsigned char *buf, unsigned long size, const char *
 		return 1;
 	}
 
-	numbytes = fwrite(buf, 1, size, image);
-	fclose(image);
+	unsigned long numbytes = fwrite(buf, 1, size, image);
 	if (numbytes != size) {
-		msg_gerr("File %s could not be written completely.\n",
-			 filename);
-		return 1;
+		msg_gerr("Error: file %s could not be written completely.\n", filename);
+		ret = 1;
+		goto out;
 	}
-	return 0;
+	if (fflush(image)) {
+		msg_gerr("Error: flushing file \"%s\" failed: %s\n", filename, strerror(errno));
+		ret = 1;
+	}
+	// Try to fsync() only regular files and if that function is available at all (e.g. not on MinGW).
+#if defined(_POSIX_FSYNC) && (_POSIX_FSYNC != -1)
+	struct stat image_stat;
+	if (fstat(fileno(image), &image_stat) != 0) {
+		msg_gerr("Error: getting metadata of file \"%s\" failed: %s\n", filename, strerror(errno));
+		ret = 1;
+		goto out;
+	}
+	if (S_ISREG(image_stat.st_mode)) {
+		if (fsync(fileno(image))) {
+			msg_gerr("Error: fsyncing file \"%s\" failed: %s\n", filename, strerror(errno));
+			ret = 1;
+		}
+	}
+#endif
+out:
+	if (fclose(image)) {
+		msg_gerr("Error: closing file \"%s\" failed: %s\n", filename, strerror(errno));
+		ret = 1;
+	}
+	return ret;
 #endif
 }