coda: fix 'kernel memory exposure attempt' in fsync

commit d337b66a4c52c7b04eec661d86c2ef6e168965a2 upstream.

When an application called fsync on a file in Coda a small request with
just the file identifier was allocated, but the declared length was set
to the size of union of all possible upcall requests.

This bug has been around for a very long time and is now caught by the
extra checking in usercopy that was introduced in Linux-4.8.

The exposure happens when the Coda cache manager process reads the fsync
upcall request at which point it is killed. As a result there is nobody
servicing any further upcalls, trapping any processes that try to access
the mounted Coda filesystem.

Signed-off-by: Jan Harkes <jaharkes@cs.cmu.edu>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/coda/upcall.c b/fs/coda/upcall.c
index a37f003530d7353ca1ae4b37ea8c7f8c2c3a9261..1175a1722411d353624c8b1548f054c5b13fc520 100644 (file)
--- a/fs/coda/upcall.c
+++ b/fs/coda/upcall.c
@@ -447,8 +447,7 @@ int venus_fsync(struct super_block *sb, struct CodaFid *fid)
        UPARG(CODA_FSYNC);
 
        inp->coda_fsync.VFid = *fid;
-       error = coda_upcall(coda_vcp(sb), sizeof(union inputArgs),
-                           &outsize, inp);
+       error = coda_upcall(coda_vcp(sb), insize, &outsize, inp);
 
        CODA_FREE(inp, insize);
        return error;