On Fri, Aug 13, 2021 at 12:41 AM Gabriel Krisman Bertazi <krisman@xxxxxxxxxxxxx> wrote: > > Instead of failing, encode an invalid file handle in fanotify_encode_fh > if no inode is provided. This bogus file handle will be reported by > FAN_FS_ERROR for non-inode errors. > > When being reported to userspace, the length information is actually > reset and the handle cleaned up, such that userspace don't have the > visibility of the internal kernel representation of this null handle. > > Also adjust the single caller that might rely on failure after passing > an empty inode. > > Suggested-by: Amir Goldstein <amir73il@xxxxxxxxx> > Signed-off-by: Gabriel Krisman Bertazi <krisman@xxxxxxxxxxxxx> > > --- > Changes since v5: > - Preserve flags initialization (jan) > - Add BUILD_BUG_ON (amir) > - Require minimum of FANOTIFY_NULL_FH_LEN for fh_len(amir) > - Improve comment to explain the null FH length (jan) > - Simplify logic > --- > fs/notify/fanotify/fanotify.c | 27 ++++++++++++++++++----- > fs/notify/fanotify/fanotify_user.c | 35 +++++++++++++++++------------- > 2 files changed, 41 insertions(+), 21 deletions(-) > > diff --git a/fs/notify/fanotify/fanotify.c b/fs/notify/fanotify/fanotify.c > index 50fce4fec0d6..2b1ab031fbe5 100644 > --- a/fs/notify/fanotify/fanotify.c > +++ b/fs/notify/fanotify/fanotify.c > @@ -334,6 +334,8 @@ static u32 fanotify_group_event_mask(struct fsnotify_group *group, > return test_mask & user_mask; > } > > +#define FANOTIFY_NULL_FH_LEN 4 > + > /* > * Check size needed to encode fanotify_fh. > * > @@ -345,7 +347,7 @@ static int fanotify_encode_fh_len(struct inode *inode) > int dwords = 0; > > if (!inode) > - return 0; > + return FANOTIFY_NULL_FH_LEN; > > exportfs_encode_inode_fh(inode, NULL, &dwords, NULL); > > @@ -367,11 +369,23 @@ static int fanotify_encode_fh(struct fanotify_fh *fh, struct inode *inode, > void *buf = fh->buf; > int err; > > - fh->type = FILEID_ROOT; > - fh->len = 0; > + BUILD_BUG_ON(FANOTIFY_NULL_FH_LEN < 4 || > + FANOTIFY_NULL_FH_LEN > FANOTIFY_INLINE_FH_LEN); > + > fh->flags = 0; > - if (!inode) > - return 0; > + > + if (!inode) { > + /* > + * Invalid FHs are used on FAN_FS_ERROR for errors not > + * linked to any inode. The f_handle won't be reported > + * back to userspace. The extra bytes are cleared prior > + * to reporting. > + */ > + type = FILEID_INVALID; > + fh_len = FANOTIFY_NULL_FH_LEN; Please memset() the NULL_FH buffer to zero. > + > + goto success; > + } > > /* > * !gpf means preallocated variable size fh, but fh_len could > @@ -400,6 +414,7 @@ static int fanotify_encode_fh(struct fanotify_fh *fh, struct inode *inode, > if (!type || type == FILEID_INVALID || fh_len != dwords << 2) > goto out_err; > > +success: > fh->type = type; > fh->len = fh_len; > > @@ -529,7 +544,7 @@ static struct fanotify_event *fanotify_alloc_name_event(struct inode *id, > struct fanotify_info *info; > struct fanotify_fh *dfh, *ffh; > unsigned int dir_fh_len = fanotify_encode_fh_len(id); > - unsigned int child_fh_len = fanotify_encode_fh_len(child); > + unsigned int child_fh_len = child ? fanotify_encode_fh_len(child) : 0; > unsigned int size; > > size = sizeof(*fne) + FANOTIFY_FH_HDR_LEN + dir_fh_len; > diff --git a/fs/notify/fanotify/fanotify_user.c b/fs/notify/fanotify/fanotify_user.c > index c47a5a45c0d3..4cacea5fcaca 100644 > --- a/fs/notify/fanotify/fanotify_user.c > +++ b/fs/notify/fanotify/fanotify_user.c > @@ -360,7 +360,10 @@ static int copy_info_to_user(__kernel_fsid_t *fsid, struct fanotify_fh *fh, > return -EFAULT; > > handle.handle_type = fh->type; > - handle.handle_bytes = fh_len; > + > + /* FILEID_INVALID handle type is reported without its f_handle. */ > + if (fh->type != FILEID_INVALID) > + handle.handle_bytes = fh_len; I know I suggested those exact lines, but looking at the patch, I think it would be better to do: + if (fh->type != FILEID_INVALID) + fh_len = 0; handle.handle_bytes = fh_len; > if (copy_to_user(buf, &handle, sizeof(handle))) > return -EFAULT; > > @@ -369,20 +372,22 @@ static int copy_info_to_user(__kernel_fsid_t *fsid, struct fanotify_fh *fh, > if (WARN_ON_ONCE(len < fh_len)) > return -EFAULT; > > - /* > - * For an inline fh and inline file name, copy through stack to exclude > - * the copy from usercopy hardening protections. > - */ > - fh_buf = fanotify_fh_buf(fh); > - if (fh_len <= FANOTIFY_INLINE_FH_LEN) { > - memcpy(bounce, fh_buf, fh_len); > - fh_buf = bounce; > + if (fh->type != FILEID_INVALID) { ... and here: if (fh_len) { > + /* > + * For an inline fh and inline file name, copy through > + * stack to exclude the copy from usercopy hardening > + * protections. > + */ > + fh_buf = fanotify_fh_buf(fh); > + if (fh_len <= FANOTIFY_INLINE_FH_LEN) { > + memcpy(bounce, fh_buf, fh_len); > + fh_buf = bounce; > + } > + if (copy_to_user(buf, fh_buf, fh_len)) > + return -EFAULT; > + buf += fh_len; > + len -= fh_len; > } > - if (copy_to_user(buf, fh_buf, fh_len)) > - return -EFAULT; > - > - buf += fh_len; > - len -= fh_len; > > if (name_len) { > /* Copy the filename with terminating null */ > @@ -398,7 +403,7 @@ static int copy_info_to_user(__kernel_fsid_t *fsid, struct fanotify_fh *fh, > } > > /* Pad with 0's */ > - WARN_ON_ONCE(len < 0 || len >= FANOTIFY_EVENT_ALIGN); > + WARN_ON_ONCE(len < 0); According to my calculations, FAN_FS_ERROR event with NULL_FH is expected to get here with len == 4, so you can change this to: WARN_ON_ONCE(len < 0 || len > FANOTIFY_EVENT_ALIGN); But first, I would like to get Jan's feedback on this concept of keeping unneeded 4 bytes zero padding in reported event in case of NULL_FH in order to keep the FID reporting code simpler. Thanks, Amir.