Commit c09f11ef authored Mar 01, 2021 by Randy Dunlap Committed by Trond Myklebust Apr 05, 2021

NFS: fs_context: validate UDP retrans to prevent shift out-of-bounds



Fix shift out-of-bounds in xprt_calc_majortimeo(). This is caused
by a garbage timeout (retrans) mount option being passed to nfs mount,
in this case from syzkaller.

If the protocol is XPRT_TRANSPORT_UDP, then 'retrans' is a shift
value for a 64-bit long integer, so 'retrans' cannot be >= 64.
If it is >= 64, fail the mount and return an error.

Fixes: 9954bf92 ("NFS: Move mount parameterisation bits into their own file")
Reported-by:  <syzbot+ba2e91df8f74809417fa@syzkaller.appspotmail.com>
Reported-by:  <syzbot+f3a0fa110fd630ab56c8@syzkaller.appspotmail.com>
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Trond Myklebust <trond.myklebust@hammerspace.com>
Cc: Anna Schumaker <anna.schumaker@netapp.com>
Cc: linux-nfs@vger.kernel.org
Cc: David Howells <dhowells@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: stable@vger.kernel.org
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>

parent f892c41c

fs/nfs/fs_context.c

+12 −0

Original line number	Diff line number	Diff line
		@@ -973,6 +973,15 @@ static int nfs23_parse_monolithic(struct fs_context *fc,
		memset(mntfh->data + mntfh->size, 0,
		sizeof(mntfh->data) - mntfh->size);

		/*
		* for proto == XPRT_TRANSPORT_UDP, which is what uses
		* to_exponential, implying shift: limit the shift value
		* to BITS_PER_LONG (majortimeo is unsigned long)
		*/
		if (!(data->flags & NFS_MOUNT_TCP)) /* this will be UDP */
		if (data->retrans >= 64) /* shift value is too large */
		goto out_invalid_data;

		/*
		* Translate to nfs_fs_context, which nfs_fill_super
		* can deal with.
		@@ -1073,6 +1082,9 @@ static int nfs23_parse_monolithic(struct fs_context *fc,

		out_invalid_fh:
		return nfs_invalf(fc, "NFS: invalid root filehandle");

		out_invalid_data:
		return nfs_invalf(fc, "NFS: invalid binary mount data");
		}

		#if IS_ENABLED(CONFIG_NFS_V4)