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>
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 @@
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: