On 2/1/24 19:37, 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); }
Applied to the ceph-client's 'testing' branch and will run the tests. Thanks - Xiubo
