[PATCH] fs: clamp FIONREAD result to int range

[Avi Weiss <thnkslprpt@gmail.com>]

FIONREAD returns the difference between the file size and the current
position in an int. When the difference is outside the int range, the
result wraps, so a file with 4 GiB remaining can be reported as empty.

Clamp the result to the signed int range before returning it to userspace.
Preserve negative counts for file positions past EOF.

Signed-off-by: Avi Weiss <thnkslprpt@gmail.com>
---
 fs/ioctl.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/fs/ioctl.c b/fs/ioctl.c
index 1c152c2b1b67d..ecc2a4cfe6100 100644
--- a/fs/ioctl.c
+++ b/fs/ioctl.c
@@ -7,6 +7,7 @@
 
 #include <linux/syscalls.h>
 #include <linux/mm.h>
+#include <linux/minmax.h>
 #include <linux/capability.h>
 #include <linux/compat.h>
 #include <linux/file.h>
@@ -550,8 +551,8 @@ static int do_vfs_ioctl(struct file *filp, unsigned int fd,
 		if (!S_ISREG(inode->i_mode) || IS_ANON_FILE(inode))
 			return vfs_ioctl(filp, cmd, arg);
 
-		return put_user(i_size_read(inode) - filp->f_pos,
-				(int __user *)argp);
+		return put_user(clamp_t(loff_t, i_size_read(inode) - filp->f_pos,
+					INT_MIN, INT_MAX), (int __user *)argp);
 
 	case FS_IOC_GETFLAGS:
 		return ioctl_getflags(filp, argp);

base-commit: 36aad21d50d1af3f6954bb0c988257a908202477
-- 
2.43.0