Re: [flashrom] [PATCH] Rigorously check integrity of I/O stream data.

[Stefan Tauner]

On Sun, 22 Nov 2015 18:29:34 +0100
Stefan Tauner  wrote:
> Nevertheless I think we should merge this patch ASAP.

Or maybe with a goto from the error state of fwrite to the fclose call
(skipping fflush and fsync if fwrite fails), because there is really
no benefit of doing these calls in that case - it even produces one more
error output when trying to fsync /dev/full... OTOH fsyncing often
fails on non-regular files (e.g. /dev/null) even though everything
works as intended... *sigh*

[PATCH] Rigorously check integrity of I/O stream data.

[Stefan Tauner]

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.

Signed-off-by: Stefan Tauner 
---
 flashrom.c         | 67 +++++++++++++++++++++++++++++++++++++-----------------
 layout.c           |  6 ++---
 processor_enable.c |  4 ++--
 3 files changed, 51 insertions(+), 26 deletions(-)

diff --git a/flashrom.c b/flashrom.c
index c9c7e31..6e5fd68 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 +1256,39 @@ 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:
+	if (fclose(image)) {
+		msg_gerr("Error: closing file "%s" failed: %s\n", filename, strerror(errno));
+		ret = 1;
+	}
+	return ret;
 #endif
 }

@@ -1294,8 +1298,8 @@ 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 +1310,35 @@ 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;
+	}
+	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;
+	}
+	/* Try to fsync only regular files. */
+	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;
+		}
+	}
+out:
+	if (fclose(image)) {
+		msg_gerr("Error: closing file "%s" failed: %s\n", filename, strerror(errno));
+		ret = 1;
+	}
+	return ret;
 #endif
 }

diff --git a/layout.c b/layout.c
index 0b9f6e5..d039451 100644
--- a/layout.c
+++ b/layout.c
@@ -65,7 +65,7 @@ int read_romlayout(const char *name)
    	if (num_rom_entries >= MAX_ROMLAYOUT) {
    		msg_gerr("Maximum number of ROM images (%i) in layout "
    			 "file reached.\n", MAX_ROMLAYOUT);
-			fclose(romlayout);
+			(void)fclose(romlayout);
    		return 1;
    	}
    	if (2 != fscanf(romlayout, "%s %s\n", tempstr, rom_entries[num_rom_entries].name))
@@ -80,7 +80,7 @@ int read_romlayout(const char *name)
    	tstr2 = strtok(NULL, ":");
    	if (!tstr1 || !tstr2) {
    		msg_gerr("Error parsing layout file. Offending string: "%s"\n", tempstr);
-			fclose(romlayout);
+			(void)fclose(romlayout);
    		return 1;
    	}
    	rom_entries[num_rom_entries].start = strtol(tstr1, (char **)NULL, 16);
@@ -95,7 +95,7 @@ int read_romlayout(const char *name)
    		     rom_entries[i].end, rom_entries[i].name);
    }

-	fclose(romlayout);
+	(void)fclose(romlayout);

return 0;
 }
diff --git a/processor_enable.c b/processor_enable.c
index 1361dd5..117aa1e 100644
--- a/processor_enable.c
+++ b/processor_enable.c
@@ -57,11 +57,11 @@ static int is_loongson(void)
    	ptr++;
    	while (*ptr && isspace((unsigned char)*ptr))
    		ptr++;
-		fclose(cpuinfo);
+		(void)fclose(cpuinfo);
    	return (strncmp(ptr, "ICT Loongson-2 V0.3", strlen("ICT Loongson-2 V0.3")) == 0) ||
    	       (strncmp(ptr, "Godson2 V0.3  FPU V0.1", strlen("Godson2 V0.3  FPU V0.1")) == 0);
    }
-	fclose(cpuinfo);
+	(void)fclose(cpuinfo);
    return 0;
 }
 #endif