Hello Joel, On 3/14/19 10:48 PM, Joel Fernandes (Google) wrote: > More details of the seal can be found in the LKML patch: > https://lore.kernel.org/lkml/20181120052137.74317-1-joel@xxxxxxxxxxxxxxxxx/T/#t > > Signed-off-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx> Thanks! Patch applied Cheers, Michael > --- > man2/memfd_create.2 | 15 ++++++++++++++- > 1 file changed, 14 insertions(+), 1 deletion(-) > > diff --git a/man2/memfd_create.2 b/man2/memfd_create.2 > index 15b1362f5525..3b7f032407ed 100644 > --- a/man2/memfd_create.2 > +++ b/man2/memfd_create.2 > @@ -280,7 +280,15 @@ in order to restrict further modifications on the file. > (If placing the seal > .BR F_SEAL_WRITE , > then it will be necessary to first unmap the shared writable mapping > -created in the previous step.) > +created in the previous step. Otherwise, behavior similar to > +.BR F_SEAL_WRITE > +can be achieved, by using > +.BR F_SEAL_FUTURE_WRITE > +which will prevent future writes via > +.BR mmap (2) > +and > +.BR write (2) > +from succeeding, while keeping existing shared writable mappings). > .IP 4. > A second process obtains a file descriptor for the > .BR tmpfs (5) > @@ -425,6 +433,7 @@ main(int argc, char *argv[]) > fprintf(stderr, "\et\etg \- F_SEAL_GROW\en"); > fprintf(stderr, "\et\ets \- F_SEAL_SHRINK\en"); > fprintf(stderr, "\et\etw \- F_SEAL_WRITE\en"); > + fprintf(stderr, "\et\etW \- F_SEAL_FUTURE_WRITE\en"); > fprintf(stderr, "\et\etS \- F_SEAL_SEAL\en"); > exit(EXIT_FAILURE); > } > @@ -463,6 +472,8 @@ main(int argc, char *argv[]) > seals |= F_SEAL_SHRINK; > if (strchr(seals_arg, \(aqw\(aq) != NULL) > seals |= F_SEAL_WRITE; > + if (strchr(seals_arg, \(aqW\(aq) != NULL) > + seals |= F_SEAL_FUTURE_WRITE; > if (strchr(seals_arg, \(aqS\(aq) != NULL) > seals |= F_SEAL_SEAL; > > @@ -518,6 +529,8 @@ main(int argc, char *argv[]) > printf(" GROW"); > if (seals & F_SEAL_WRITE) > printf(" WRITE"); > + if (seals & F_SEAL_FUTURE_WRITE) > + printf(" FUTURE_WRITE"); > if (seals & F_SEAL_SHRINK) > printf(" SHRINK"); > printf("\en"); > -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Linux/UNIX System Programming Training: http://man7.org/training/
