On Fri, 4 Feb 2022 19:19:39 +0300 "Dmitry V. Levin" <l...@altlinux.org> wrote:
> On Fri, Feb 04, 2022 at 02:55:45PM +0100, Philippe Mathieu-Daudé wrote: > > On 4/2/22 06:06, Vitaly Chikunov wrote: > > > `struct dirent' returned from readdir(3) could be shorter (or longer) > > > than `sizeof(struct dirent)', thus memcpy of sizeof length will overread > > > into unallocated page causing SIGSEGV. Example stack trace: > > > > > > #0 0x00005555559ebeed v9fs_co_readdir_many > > > (/usr/bin/qemu-system-x86_64 + 0x497eed) > > > #1 0x00005555559ec2e9 v9fs_readdir (/usr/bin/qemu-system-x86_64 + > > > 0x4982e9) > > > #2 0x0000555555eb7983 coroutine_trampoline > > > (/usr/bin/qemu-system-x86_64 + 0x963983) > > > #3 0x00007ffff73e0be0 n/a (n/a + 0x0) > > > > > > While fixing, provide a helper for any future `struct dirent' cloning. > > > > > > Resolves: https://gitlab.com/qemu-project/qemu/-/issues/841 > > > Cc: qemu-sta...@nongnu.org > > > Co-authored-by: Christian Schoenebeck <qemu_...@crudebyte.com> > > > Signed-off-by: Vitaly Chikunov <v...@altlinux.org> > > > --- > > > Tested on x86-64 Linux again. > > > > > > Changes from v2: > > > - Make it work with a simulated dirent where d_reclen is 0, which was > > > caused abort in readdir qos-test, by using fallback at runtime. > > > > > > hw/9pfs/codir.c | 3 +-- > > > include/qemu/osdep.h | 13 +++++++++++++ > > > util/osdep.c | 18 ++++++++++++++++++ > > > 3 files changed, 32 insertions(+), 2 deletions(-) > > > > > +struct dirent * > > > +qemu_dirent_dup(struct dirent *dent) > > > +{ > > > + size_t sz = 0; > > > +#if defined _DIRENT_HAVE_D_RECLEN > > > + /* Avoid use of strlen() if there's d_reclen. */ > > > + sz = dent->d_reclen; > > > +#endif > > > + if (sz == 0) { > > > > If _DIRENT_HAVE_D_RECLEN is defined, this case is unlikely... > > If it was so easy to be misled this way, > I'd suggest adding an explicit comment, e.g. > > /* > * Test sz for non-zero even if d_reclen is available > * because some drivers may set d_reclen to zero. > */ > +1 >
