Check fflush on BIO_ctrl call

Bug found and fix suggested by Julian Rüth.
Push error if fflush fails
Reviewed-by: NRichard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/3266)

crypto/bio/bss_file.c

@@ -190,6 +190,7 @@ static long file_ctrl(BIO *b, int cmd, long num, void *ptr)
     FILE *fp = (FILE *)b->ptr;
     FILE **fpp;
     char p[4];
+    int st;
 
     switch (cmd) {
     case BIO_C_FILE_SEEK:
@@ -317,10 +318,14 @@ static long file_ctrl(BIO *b, int cmd, long num, void *ptr)
         b->shutdown = (int)num;
         break;
     case BIO_CTRL_FLUSH:
-        if (b->flags & BIO_FLAGS_UPLINK)
-            UP_fflush(b->ptr);
-        else
-            fflush((FILE *)b->ptr);
+        st = b->flags & BIO_FLAGS_UPLINK
+                ? UP_fflush(b->ptr) : fflush((FILE *)b->ptr);
+        if (st == EOF) {
+            SYSerr(SYS_F_FFLUSH, get_last_sys_error());
+            ERR_add_error_data(1, "fflush()");
+            BIOerr(BIO_F_FILE_CTRL, ERR_R_SYS_LIB);
+            ret = 0;
+        }
         break;
     case BIO_CTRL_DUP:
         ret = 1;

crypto/err/err.c

@@ -82,6 +82,7 @@ static ERR_STRING_DATA ERR_str_functs[] = {
     {ERR_PACK(0, SYS_F_GETSOCKOPT, 0), "getsockopt"},
     {ERR_PACK(0, SYS_F_GETSOCKNAME, 0), "getsockname"},
     {ERR_PACK(0, SYS_F_GETHOSTBYNAME, 0), "gethostbyname"},
+    {ERR_PACK(0, SYS_F_FFLUSH, 0), "fflush"},
     {0, NULL},
 };
 

include/openssl/err.h

@@ -159,6 +159,7 @@ typedef struct err_state_st {
 # define SYS_F_GETSOCKOPT        15
 # define SYS_F_GETSOCKNAME       16
 # define SYS_F_GETHOSTBYNAME     17
+# define SYS_F_FFLUSH            18
 
 /* reasons */
 # define ERR_R_SYS_LIB   ERR_LIB_SYS/* 2 */