linux-kernel - [PATCH] fs/fcntl: restore checking against COMPAT_LOFF_T_MAX for F

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Date:   Tue, 14 Nov 2017 04:30:08 +0300
From:   Vitaly Lipatov <lav@...rsoft.ru>
To:     lav@...rsoft.ru
Cc:     Alexander Viro <viro@...iv.linux.org.uk>,
        Jeff Layton <jlayton@...chiereds.net>,
        "J. Bruce Fields" <bfields@...ldses.org>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] fs/fcntl: restore checking against COMPAT_LOFF_T_MAX for F_GETLK64

for fcntl64 with F_GETLK64 we need use checking against COMPAT_LOFF_T_MAX.

Fixes: 94073ad77fff2 "fs/locks: don't mess with the address limit in compat_fcntl64"

Signed-off-by: Vitaly Lipatov <lav@...rsoft.ru>
---
 fs/fcntl.c | 21 ++++++++++++++++++++-
 1 file changed, 20 insertions(+), 1 deletion(-)

diff --git a/fs/fcntl.c b/fs/fcntl.c
index 30f47d0..fa17f67 100644
--- a/fs/fcntl.c
+++ b/fs/fcntl.c
@@ -604,6 +604,25 @@ static int fixup_compat_flock(struct flock *flock)
 	return 0;
 }
 
+/*
+ * GETLK64 was successful and we need to return the data, but it needs to fit in
+ * the compat structure.
+ * l_start shouldn't be too big, unless the original start + end is greater than
+ * COMPAT_LOFF_T_MAX, in which case the app was asking for trouble, so we return
+ * -EOVERFLOW in that case.  l_len could be too big, in which case we just
+ * truncate it, and only allow the app to see that part of the conflicting lock
+ * that might make sense to it anyway
+ */
+
+static int fixup_compat_l_flock(struct flock *flock)
+{
+	if (flock->l_start > COMPAT_LOFF_T_MAX)
+		return -EOVERFLOW;
+	if (flock->l_len > COMPAT_LOFF_T_MAX)
+		flock->l_len = COMPAT_LOFF_T_MAX;
+	return 0;
+}
+
 COMPAT_SYSCALL_DEFINE3(fcntl64, unsigned int, fd, unsigned int, cmd,
 		       compat_ulong_t, arg)
 {
@@ -644,7 +663,7 @@ COMPAT_SYSCALL_DEFINE3(fcntl64, unsigned int, fd, unsigned int, cmd,
 		err = fcntl_getlk(f.file, convert_fcntl_cmd(cmd), &flock);
 		if (err)
 			break;
-		err = fixup_compat_flock(&flock);
+		err = fixup_compat_l_flock(&flock);
 		if (err)
 			return err;
 		err = put_compat_flock64(&flock, compat_ptr(arg));
-- 
2.10.4