pipe: set lower and upper limit on max pages in the pipe page array

We need at least two to guarantee proper POSIX behaviour, so
never allow a smaller limit than that.

Also expose a /proc/sys/fs/pipe-max-pages sysctl file that allows
root to define a sane upper limit. Make it default to 16 times the
default size, which is 16 pages.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

1 files changed, 15 insertions, 0 deletions

diff --git a/fs/pipe.c b/fs/pipe.c
index 054b8a6..d79872e 100644
--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -19,11 +19,18 @@
 #include <linux/pagemap.h>
 #include <linux/audit.h>
 #include <linux/syscalls.h>
+#include <linux/fcntl.h>
 
 #include <asm/uaccess.h>
 #include <asm/ioctls.h>
 
 /*
+ * The max size that a non-root user is allowed to grow the pipe. Can
+ * be set by root in /proc/sys/fs/pipe-max-pages
+ */
+unsigned int pipe_max_pages = PIPE_DEF_BUFFERS * 16;
+
+/*
  * We use a start+len construction, which provides full use of the 
  * allocated memory.
  * -- Florian Coosmann (FGC)
@@ -1162,6 +1169,14 @@ long pipe_fcntl(struct file *file, unsigned int cmd, unsigned long arg)
 
 	switch (cmd) {
 	case F_SETPIPE_SZ:
+		if (!capable(CAP_SYS_ADMIN) && arg > pipe_max_pages)
+			return -EINVAL;
+		/*
+		 * The pipe needs to be at least 2 pages large to
+		 * guarantee POSIX behaviour.
+		 */
+		if (arg < 2)
+			return -EINVAL;
 		ret = pipe_set_size(pipe, arg);
 		break;
 	case F_GETPIPE_SZ: