add match_strlcpy() us it to make v9fs make uname and remotename parsing more robust

match_strcpy() is a somewhat creepy function: the caller needs to make sure
that the destination buffer is big enough, and when he screws up or
forgets, match_strcpy() happily overruns the buffer.

There's exactly one customer: v9fs_parse_options().  I believe it currently
can't overflow its buffer, but that's not exactly obvious.

The source string is a substing of the mount options.  The kernel silently
truncates those to PAGE_SIZE bytes, including the terminating zero.  See
compat_sys_mount() and do_mount().

The destination buffer is obtained from __getname(), which allocates from
name_cachep, which is initialized by vfs_caches_init() for size PATH_MAX.

We're safe as long as PATH_MAX <= PAGE_SIZE.  PATH_MAX is 4096.  As far as
I know, the smallest PAGE_SIZE is also 4096.

Here's a patch that makes the code a bit more obviously correct.  It
doesn't depend on PATH_MAX <= PAGE_SIZE.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Cc: Latchesar Ionkov <lucho@ionkov.net>
Cc: Jim Meyering <meyering@redhat.com>
Cc: "Randy.Dunlap" <rdunlap@xenotime.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Eric Van Hensbergen <ericvh@gmail.com>

1 files changed, 2 insertions, 2 deletions

diff --git a/fs/9p/v9fs.c b/fs/9p/v9fs.c
index 9b0f0222e8b..e307fbd34fa 100644
--- a/fs/9p/v9fs.c
+++ b/fs/9p/v9fs.c
@@ -125,10 +125,10 @@ static void v9fs_parse_options(struct v9fs_session_info *v9ses)
                         v9ses->afid = option;
                         break;
                 case Opt_uname:
-                        match_strcpy(v9ses->uname, &args[0]);
+                        match_strlcpy(v9ses->uname, &args[0], PATH_MAX);
                         break;
                 case Opt_remotename:
-                        match_strcpy(v9ses->aname, &args[0]);
+                        match_strlcpy(v9ses->aname, &args[0], PATH_MAX);
                         break;
                 case Opt_nodevmap:
                         v9ses->nodev = 1;