io: Return EBAFD for negative file descriptor on fstat (BZ #27559)

Now that fstat is implemented on top fstatat we need to handle negative
inputs.  The implementation now rejects AT_FDCWD, which would otherwise
be accepted by the kernel.

Checked on x86_64-linux-gnu and on i686-linux-gnu.

2 files changed, 18 insertions, 0 deletions

diff --git a/sysdeps/unix/sysv/linux/fstat.c b/sysdeps/unix/sysv/linux/fstat.c
index fd64362205..31a172dcc8 100644
--- a/sysdeps/unix/sysv/linux/fstat.c
+++ b/sysdeps/unix/sysv/linux/fstat.c
@@ -19,11 +19,17 @@
 #include <sys/stat.h>
 #include <kernel_stat.h>
 #include <fcntl.h>
+#include <errno.h>
 
 #if !XSTAT_IS_XSTAT64
 int
 __fstat (int fd, struct stat *buf)
 {
+  if (fd < 0)
+    {
+      __set_errno (EBADF);
+      return -1;
+    }
   return __fstatat (fd, "", buf, AT_EMPTY_PATH);
 }
 
diff --git a/sysdeps/unix/sysv/linux/fstat64.c b/sysdeps/unix/sysv/linux/fstat64.c
index 993abcb445..46de80b663 100644
--- a/sysdeps/unix/sysv/linux/fstat64.c
+++ b/sysdeps/unix/sysv/linux/fstat64.c
@@ -22,10 +22,16 @@
 #include <fcntl.h>
 #include <kernel_stat.h>
 #include <stat_t64_cp.h>
+#include <errno.h>
 
 int
 __fstat64_time64 (int fd, struct __stat64_t64 *buf)
 {
+  if (fd < 0)
+    {
+      __set_errno (EBADF);
+      return -1;
+    }
   return __fstatat64_time64 (fd, "", buf, AT_EMPTY_PATH);
 }
 #if __TIMESIZE != 64
@@ -34,6 +40,12 @@ hidden_def (__fstat64_time64)
 int
 __fstat64 (int fd, struct stat64 *buf)
 {
+  if (fd < 0)
+    {
+      __set_errno (EBADF);
+      return -1;
+    }
+
   struct __stat64_t64 st_t64;
   return __fstat64_time64 (fd, &st_t64)
 	 ?: __cp_stat64_t64_stat64 (&st_t64, buf);