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: Ben Hutchings <ben@decadent.org.uk>

diff --git a/fs/coda/upcall.c b/fs/coda/upcall.c
index 9727e0c525793354cee16b4ccb3df71598ddd843..446d6b61c9c28ae390211b69d9f238af06d11e18 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;