On Thu, 2024-02-01 at 17:07 +0530, ridave@xxxxxxxxxx wrote: > From: Rishabh Dave <ridave@xxxxxxxxxx> > > In fs/ceph/caps.c, in "encode_cap_msg()", "use after free" error was > caught by KASAN at this line - 'ceph_buffer_get(arg->xattr_buf);'. This > implies before the refcount could be increment here, it was freed. > > In same file, in "handle_cap_grant()" refcount is decremented by this > line - "ceph_buffer_put(ci->i_xattrs.blob);". It appears that a race > occurred and resource was freed by the latter line before the former > line > could increment it. > > encode_cap_msg() is called by __send_cap() and __send_cap() is called by > ceph_check_caps() after calling __prep_cap(). __prep_cap() is where > "arg->xattr_buf" is assigned to "ci->i_xattrs.blob" . This is the spot > where the refcount must be increased to prevent "use after free" error. > > URL: https://tracker.ceph.com/issues/59259 > Signed-off-by: Rishabh Dave <ridave@xxxxxxxxxx> > --- > fs/ceph/caps.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/fs/ceph/caps.c b/fs/ceph/caps.c > index 5501c86b337d..0ca7dce48172 100644 > --- a/fs/ceph/caps.c > +++ b/fs/ceph/caps.c > @@ -1452,7 +1452,7 @@ static void __prep_cap(struct cap_msg_args *arg, struct ceph_cap *cap, > if (flushing & CEPH_CAP_XATTR_EXCL) { > arg->old_xattr_buf = __ceph_build_xattrs_blob(ci); > arg->xattr_version = ci->i_xattrs.version; > - arg->xattr_buf = ci->i_xattrs.blob; > + arg->xattr_buf = ceph_buffer_get(ci->i_xattrs.blob); > } else { > arg->xattr_buf = NULL; > arg->old_xattr_buf = NULL; > @@ -1553,6 +1553,7 @@ static void __send_cap(struct cap_msg_args *arg, struct ceph_inode_info *ci) > encode_cap_msg(msg, arg); > ceph_con_send(&arg->session->s_con, msg); > ceph_buffer_put(arg->old_xattr_buf); > + ceph_buffer_put(arg->xattr_buf); > if (arg->wake) > wake_up_all(&ci->i_cap_wq); > } Nice catch! Reviewed-by: Jeff Layton <jlayton@xxxxxxxxxx>
