[PATCH v2 5/7] pipe: reject F_SETPIPE_SZ with size over UINT_MAX

[Eric Biggers]

From: Eric Biggers <ebiggers@xxxxxxxxxx>

A pipe's size is represented as an 'unsigned int'.  As expected, writing
a value greater than UINT_MAX to /proc/sys/fs/pipe-max-size fails with
EINVAL.  However, the F_SETPIPE_SZ fcntl silently truncates such values
to 32 bits, rather than failing with EINVAL as expected.  (It *does*
fail with EINVAL for values above (1 << 31) but <= UINT_MAX.)

Fix this by moving the check against UINT_MAX into round_pipe_size()
which is called in both cases.

Acked-by: Kees Cook <keescook@xxxxxxxxxxxx>
Signed-off-by: Eric Biggers <ebiggers@xxxxxxxxxx>
---
 fs/pipe.c                 | 5 ++++-
 include/linux/pipe_fs_i.h | 2 +-
 kernel/sysctl.c           | 3 ---
 3 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/fs/pipe.c b/fs/pipe.c
index 9f20e7128578..f1ee1e599495 100644
--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -1020,10 +1020,13 @@ const struct file_operations pipefifo_fops = {
  * Currently we rely on the pipe array holding a power-of-2 number
  * of pages. Returns 0 on error.
  */
-unsigned int round_pipe_size(unsigned int size)
+unsigned int round_pipe_size(unsigned long size)
 {
 	unsigned long nr_pages;
 
+	if (size > UINT_MAX)
+		return 0;
+
 	/* Minimum pipe size, as required by POSIX */
 	if (size < PAGE_SIZE)
 		size = PAGE_SIZE;
diff --git a/include/linux/pipe_fs_i.h b/include/linux/pipe_fs_i.h
index 5028bd4b2c96..5a3bb3b7c9ad 100644
--- a/include/linux/pipe_fs_i.h
+++ b/include/linux/pipe_fs_i.h
@@ -190,6 +190,6 @@ long pipe_fcntl(struct file *, unsigned int, unsigned long arg);
 struct pipe_inode_info *get_pipe_info(struct file *file);
 
 int create_pipe_files(struct file **, int);
-unsigned int round_pipe_size(unsigned int size);
+unsigned int round_pipe_size(unsigned long size);
 
 #endif
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 33e2f0f02000..31fe10fd745f 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -2630,9 +2630,6 @@ static int do_proc_dopipe_max_size_conv(unsigned long *lvalp,
 	if (write) {
 		unsigned int val;
 
-		if (*lvalp > UINT_MAX)
-			return -EINVAL;
-
 		val = round_pipe_size(*lvalp);
 		if (val == 0)
 			return -EINVAL;
-- 
2.15.1