[RFC][PATCH 2/4] anon_inode fcntl() checks: report failure for fcntl(F_SETFL) on timerfd

[Matt Helsley]

Report failure when userspace attempts to set unsupported flags
on timerfd files with fcntl().

Signed-off-by: Matt Helsley <matthltc@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Davide Libenzi <davidel@xxxxxxxxxxxxxxx>
---
 fs/timerfd.c |   16 ++++++++++++----
 1 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/fs/timerfd.c b/fs/timerfd.c
index 1bfc95a..198a564 100644
--- a/fs/timerfd.c
+++ b/fs/timerfd.c
@@ -156,7 +156,19 @@ static ssize_t timerfd_read(struct file *file, char __user *buf, size_t count,
 	return res;
 }
 
+static int timerfd_check_flags(int flags)
+{
+	/* Check the TFD_* constants for consistency.  */
+	BUILD_BUG_ON(TFD_CLOEXEC != O_CLOEXEC);
+	BUILD_BUG_ON(TFD_NONBLOCK != O_NONBLOCK);
+
+	if (flags & ~(TFD_CLOEXEC | TFD_NONBLOCK))
+		return -EINVAL;
+	return 0;
+}
+
 static const struct file_operations timerfd_fops = {
+	.check_flags    = timerfd_check_flags,
 	.release	= timerfd_release,
 	.poll		= timerfd_poll,
 	.read		= timerfd_read,
@@ -182,10 +194,6 @@ SYSCALL_DEFINE2(timerfd_create, int, clockid, int, flags)
 	int ufd;
 	struct timerfd_ctx *ctx;
 
-	/* Check the TFD_* constants for consistency.  */
-	BUILD_BUG_ON(TFD_CLOEXEC != O_CLOEXEC);
-	BUILD_BUG_ON(TFD_NONBLOCK != O_NONBLOCK);
-
 	if ((flags & ~TFD_CREATE_FLAGS) ||
 	    (clockid != CLOCK_MONOTONIC &&
 	     clockid != CLOCK_REALTIME))
-- 
1.6.3.3

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