libio: Limit buffer size to 8192 bytes [BZ #4099]

This avoids overly large buffers with network file systems which report
very large block sizes.

3 files changed, 13 insertions, 1 deletions

diff --git a/ChangeLog b/ChangeLog
index 40f460f759..c2cb608065 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+2016-11-30  Florian Weimer  <fweimer@redhat.com>
+
+	[BZ #4099]
+	* libio/filedoalloc.c (_IO_file_doallocate): Limit buffer size to
+	_IO_BUFSIZ (8192).
+
 2016-11-30  Carlos O'Donell  <carlos@redhat.com>
 
 	* PROJECTS: Remove file.
diff --git a/NEWS b/NEWS
index 9a45e730af..b2a0b0f1f8 100644
--- a/NEWS
+++ b/NEWS
@@ -80,6 +80,12 @@ Version 2.25
   affect the ABI of other libraries that use this type in their interfaces,
   if they are compiled or used with those options.
 
+* The buffer size for byte-oriented stdio streams is now limited to 8192
+  bytes by default.  Previously, on Linux, the default buffer size on most
+  file systems was 4096 bytes (and thus remains unchanged), except on
+  network file systems, where the buffer size was unpredictable and could be
+  as large as several megabytes.
+
 * The <sys/quota.h> header now includes the <linux/quota.h> header.  Support
   for the Linux quota interface which predates kernel version 2.4.22 has
   been removed.
diff --git a/libio/filedoalloc.c b/libio/filedoalloc.c
index 4f9d738968..ded0725356 100644
--- a/libio/filedoalloc.c
+++ b/libio/filedoalloc.c
@@ -94,7 +94,7 @@ _IO_file_doallocate (_IO_FILE *fp)
 	    fp->_flags |= _IO_LINE_BUF;
 	}
 #if _IO_HAVE_ST_BLKSIZE
-      if (st.st_blksize > 0)
+      if (st.st_blksize > 0 && st.st_blksize < _IO_BUFSIZ)
 	size = st.st_blksize;
 #endif
     }