Re: [PATCH] pmdinfogen: fix resource leak of FILE object

On Fri, Feb 02, 2018 at 03:47:43PM +0000, Bruce Richardson wrote:

On Fri, Feb 02, 2018 at 07:44:39AM -0500, Neil Horman wrote:

quoted

On Fri, Feb 02, 2018 at 12:00:58PM +0000, Bruce Richardson wrote:

quoted

Coverity flags an issue where the resources used by the FILE object for
the temporary input file are leaked. This is a very minor issue, but is
easily fixed, while also avoiding later problems where we try to close
an invalid file descriptor in the failure case.

The fix is to use "dup()" to get a new file descriptor number rather than
using the value directly from fileno. This allows us to close the file
opened with tmpfile() within in scope block, while allowing the duplicate
to pass to the outer block and be closed when the function terminates.

As a side-effect I/O in the function is therefore changed from using stdio
fread/fwrite to read/write system calls.

Coverity issue: 260399
Fixes: 0d68533617e3 ("pmdinfogen: allow using stdin and stdout")

Signed-off-by: Bruce Richardson <redacted>
---
 buildtools/pmdinfogen/pmdinfogen.c | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/buildtools/pmdinfogen/pmdinfogen.c b/buildtools/pmdinfogen/pmdinfogen.c
index 45b267346..0f35ca46b 100644
--- a/buildtools/pmdinfogen/pmdinfogen.c
+++ b/buildtools/pmdinfogen/pmdinfogen.c

@@ -50,20 +50,24 @@ static void *grab_file(const char *filename, unsigned long *size)
 		/* from stdin, use a temporary file to mmap */
 		FILE *infile;
 		char buffer[1024];
-		size_t n;
+		int n;
 
 		infile = tmpfile();
 		if (infile == NULL) {
 			perror("tmpfile");
 			return NULL;
 		}
-		while (!feof(stdin)) {
-			n = fread(buffer, 1, sizeof(buffer), stdin);
-			if (fwrite(buffer, 1, n, infile) != n)
+		fd = dup(fileno(infile));
+		fclose(infile);
+		if (fd < 0)
+			return NULL;
+
+		n = read(STDIN_FILENO, buffer, sizeof(buffer));
+		while (n > 0) {
+			if (write(fd, buffer, n) != n)
 				goto failed;
+			n = read(STDIN_FILENO, buffer, sizeof(buffer));
 		}
-		fflush(infile);
-		fd = fileno(infile);
 	}
 
 	if (fstat(fd, &st))

-- 
2.14.3

Wouldn't it be just as good, and easier to check fd for == -1 as a condition of
calling close?

like 
failed:
	if (fd >= 0)
		close(fd);

That would fix the problem of calling goto failed with fd set to -1, but
would not fix the resource issue that coverity was complaining about. We
were allocating a stdio FILE object, then taking just the fileno of it
and letting the file number go out of scope. This cleans this that up,

s/file number/FILE object ptr/

so that we just use file numbers and properly close the FILE * once it's
outlived its usefulness.

BTW: I did investigate using open and O_TMPFILE in place of tmpfile()
call, but while it would work great on Linux, it's not available
elsewhere, so tmpfile looks the best option.

Regards,
/Bruce