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:
diff --git a/include/linux/pipe_fs_i.h b/include/linux/pipe_fs_i.h
index 65f4282..16de393 100644
--- a/include/linux/pipe_fs_i.h
+++ b/include/linux/pipe_fs_i.h
@@ -139,6 +139,8 @@
void pipe_unlock(struct pipe_inode_info *);
void pipe_double_lock(struct pipe_inode_info *, struct pipe_inode_info *);
+extern unsigned int pipe_max_pages;
+
/* Drop the inode semaphore and wait for a pipe event, atomically */
void pipe_wait(struct pipe_inode_info *pipe);
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 8686b0f..c649d1c 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -52,6 +52,7 @@
#include <linux/slow-work.h>
#include <linux/perf_event.h>
#include <linux/kprobes.h>
+#include <linux/pipe_fs_i.h>
#include <asm/uaccess.h>
#include <asm/processor.h>
@@ -1423,6 +1424,14 @@
.child = binfmt_misc_table,
},
#endif
+ {
+ .procname = "pipe-max-pages",
+ .data = &pipe_max_pages,
+ .maxlen = sizeof(int),
+ .mode = 0644,
+ .proc_handler = &proc_dointvec_minmax,
+ .extra1 = &two,
+ },
/*
* NOTE: do not add new entries to this table unless you have read
* Documentation/sysctl/ctl_unnumbered.txt