Re: [PATCH] fixdep: handle short reads in read_file

[Masahiro Yamada <masahiroy@xxxxxxxxxx>]

On Sat, Sep 7, 2024 at 12:29 AM Sam James <sam@xxxxxxxxxx> wrote:
>
> 50% or so of kernel builds within our package manager fail for me with
> 'fixdep: read: success' because read(), for some reason - possibly ptrace,
> only read a short amount, not the full size.
>
> Unfortunately, this didn't trigger a -Wunused-result warning because
> we _are_ checking the return value, but with a bad comparison (it's completely
> fine for read() to not read the whole file in one gulp).
>
> Fixes: 01b5cbe7012fb1eeffc5c143865569835bcd405e


Fixes: 01b5cbe7012f ("fixdep: use malloc() and read() to load dep_file
to buffer")


I guess, another approach would be to use fread() instead of read().

Does the attached diff fix the issue too?





> Signed-off-by: Sam James <sam@xxxxxxxxxx>
> ---
>  scripts/basic/fixdep.c | 12 +++++++++---
>  1 file changed, 9 insertions(+), 3 deletions(-)
>
> diff --git a/scripts/basic/fixdep.c b/scripts/basic/fixdep.c
> index 84b6efa849f4d..04d7742c99ac2 100644
> --- a/scripts/basic/fixdep.c
> +++ b/scripts/basic/fixdep.c
> @@ -233,9 +233,15 @@ static void *read_file(const char *filename)
>                 perror("fixdep: malloc");
>                 exit(2);
>         }
> -       if (read(fd, buf, st.st_size) != st.st_size) {
> -               perror("fixdep: read");
> -               exit(2);
> +       ssize_t bytes = 0;
> +       while (bytes < st.st_size) {
> +               ssize_t cur = read(fd, buf + bytes, st.st_size - bytes);
> +               if (cur == -1) {
> +                       perror("fixdep: read");
> +                       exit(2);
> +               } else {
> +                       bytes += cur;
> +               }
>         }
>         buf[st.st_size] = '\0';
>         close(fd);
> --
> 2.46.0
>


-- 
Best Regards
Masahiro Yamada

diff --git a/scripts/basic/fixdep.c b/scripts/basic/fixdep.c
index cdd5da7e009b..7a0ca9f0fbbe 100644
--- a/scripts/basic/fixdep.c
+++ b/scripts/basic/fixdep.c
@@ -89,10 +89,7 @@
  *  but I don't think the added complexity is worth it)
  */
 
-#include <sys/types.h>
 #include <sys/stat.h>
-#include <unistd.h>
-#include <fcntl.h>
 #include <string.h>
 #include <stdbool.h>
 #include <stdlib.h>
@@ -213,27 +210,28 @@ static void parse_config_file(const char *p)
 static void *read_file(const char *filename)
 {
 	struct stat st;
-	int fd;
+	FILE *file;
 	char *buf;
 
-	fd = open(filename, O_RDONLY);
-	if (fd < 0) {
+	file = fopen(filename, "rb");
+	if (!file) {
 		fprintf(stderr, "fixdep: error opening file: ");
 		perror(filename);
 		exit(2);
 	}
-	if (fstat(fd, &st) < 0) {
-		fprintf(stderr, "fixdep: error fstat'ing file: ");
+	if (stat(filename, &st) < 0) {
+		fprintf(stderr, "fixdep: error stat'ing file: ");
 		perror(filename);
 		exit(2);
 	}
+
 	buf = xmalloc(st.st_size + 1);
-	if (read(fd, buf, st.st_size) != st.st_size) {
+	if (fread(buf, 1, st.st_size, file) != st.st_size) {
 		perror("fixdep: read");
 		exit(2);
 	}
 	buf[st.st_size] = '\0';
-	close(fd);
+	fclose(file);
 
 	return buf;
 }