fix fread buffer overflow

Issue:#I7L4P3
Test:libc-test
Signed-off-by: Nrobottoy <wangyaofeng.wang@huawei.com>
Change-Id: I76d468a7f4e5bafd996447584928cfed6f7f54d5

libc-test/src/functionalext/supplement/stdio/fread.c

@@ -13,6 +13,8 @@
  * limitations under the License.
  */
 
+#include <sys/stat.h>
+#include <sys/wait.h>
 #include <stdlib.h>
 #include "functionalext.h"
 
@@ -116,11 +118,48 @@ void fread_0400(void)
     remove(ptr);
 }
 
+/**
+ * @tc.name      : fread_0500
+ * @tc.desc      : Verify that the return value of syscall have been processed correctly
+ * @tc.level     : Level 2
+ */
+#define FREAD_0500_BUFSZ (4097)
+void fread_0500(void)
+{
+    pid_t pid = fork();
+    if (pid == -1) {
+    	perror("fread_0500 fork:");
+    	exit(-1);
+    }
+    
+    /* child */
+    if (pid == 0) {
+        /* make sure parent opening the status file */
+    	sleep(1);
+    	exit(-1);
+    }
+    
+    char buf[FREAD_0500_BUFSZ] = {0};
+    sprintf(buf, "/proc/%d/status", pid);
+    FILE *fStatus = fopen(buf, "rb");
+    EXPECT_PTRNE("fread_0500", fStatus, NULL);
+    
+    /* wait child exit, and status file of child will disappear */
+    int status = 0;
+    pid_t w = wait(&status);
+
+    /* read >4K data from file, check if return correctly */
+    size_t rsize = fread(buf, 1, FREAD_0500_BUFSZ, fStatus);
+    EXPECT_EQ("fread_0500", rsize, 0);
+    fclose(fStatus);
+}
+
 TEST_FUN G_Fun_Array[] = {
     fread_0100,
     fread_0200,
     fread_0300,
     fread_0400,
+    fread_0500,
 };
 
 int main(int argc, char *argv[])
@@ -131,4 +170,4 @@ int main(int argc, char *argv[])
     }
 
     return t_status;
-}
\ No newline at end of file
+}

porting/linux/user/src/stdio/__stdio_read.c

@@ -3,7 +3,12 @@
 
 size_t __stdio_readx(FILE *f, unsigned char *buf, size_t len)
 {
-	return syscall(SYS_read, f->fd, buf, len);
+	ssize_t cnt = syscall(SYS_read, f->fd, buf, len);
+	if (cnt <= 0) {
+		f->flags |= cnt ? F_ERR : F_EOF;
+		return 0;
+	}
+	return cnt;
 }
 
 size_t __stdio_read(FILE *f, unsigned char *buf, size_t len)
@@ -21,8 +26,8 @@ size_t __stdio_read(FILE *f, unsigned char *buf, size_t len)
 		return 0;
 	}
 	if (cnt <= iov_buf[0].iov_len) {
-        return cnt;
-    }
+		return cnt;
+	}
 	cnt -= iov_buf[0].iov_len;
 	f->rpos = f->buf;
 	f->rend = f->buf + cnt;

porting/linux/user/src/stdio/fread.c

@@ -69,8 +69,7 @@ size_t fread(void *restrict destv, size_t size, size_t nmemb, FILE *restrict f)
 	/* Read the remainder directly */
 	for (; l; l-=k, dest+=k) {
 		k = f->readx(f, dest, l);
-		if (k <= 0) {
-			f->flags |= (k == 0 ? F_EOF : F_ERR);
+		if (!k) {
 			break;
 		}
 	}