On Tue, Aug 04, 2020 at 01:49:30PM -0700, Lokesh Gidra wrote: > On Tue, Aug 4, 2020 at 1:45 PM Eric Biggers <ebiggers@xxxxxxxxxx> wrote: > > > > On Tue, Aug 04, 2020 at 01:31:55PM -0700, Lokesh Gidra wrote: > > > when get_unused_fd_flags returns error, ctx will be freed by > > > userfaultfd's release function, which is indirectly called by fput(). > > > Also, if anon_inode_getfile_secure() returns an error, then > > > userfaultfd_ctx_put() is called, which calls mmdrop() and frees ctx. > > > > > > Also, the O_CLOEXEC was inadvertently added to the call to > > > get_unused_fd_flags() [1]. > > > > > > Adding Al Viro's suggested-by, based on [2]. > > > > > > [1] https://lore.kernel.org/lkml/1f69c0ab-5791-974f-8bc0-3997ab1d61ea@xxxxxxxxxx/ > > > [2] https://lore.kernel.org/lkml/20200719165746.GJ2786714@xxxxxxxxxxxxxxxxxx/ > > > > > > Fixes: d08ac70b1e0d (Wire UFFD up to SELinux) > > > Suggested-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx> > > > Reported-by: syzbot+75867c44841cb6373570@xxxxxxxxxxxxxxxxxxxxxxxxx > > > Signed-off-by: Lokesh Gidra <lokeshgidra@xxxxxxxxxx> > > > > What branch does this patch apply to? Neither mainline nor linux-next works. > > > On James Morris' tree (secure_uffd_v5.9 branch). > For those of us not "in the know", that apparently means branch secure_uffd_v5.9 of https://git.kernel.org/pub/scm/linux/kernel/git/jmorris/linux-security.git Perhaps it would make more sense to resend your original patch series with this fix folded in? > diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c > index ae859161908f..e15eb8fdc083 100644 > --- a/fs/userfaultfd.c > +++ b/fs/userfaultfd.c > @@ -2042,24 +2042,18 @@ SYSCALL_DEFINE1(userfaultfd, int, flags) > O_RDWR | (flags & UFFD_SHARED_FCNTL_FLAGS), > NULL); > if (IS_ERR(file)) { > - fd = PTR_ERR(file); > - goto out; > + userfaultfd_ctx_put(ctx); > + return PTR_ERR(file); > } > > - fd = get_unused_fd_flags(O_RDONLY | O_CLOEXEC); > + fd = get_unused_fd_flags(O_RDONLY); > if (fd < 0) { > fput(file); > - goto out; > + return fd; > } > > ctx->owner = file_inode(file); > fd_install(fd, file); > - > -out: > - if (fd < 0) { > - mmdrop(ctx->mm); > - kmem_cache_free(userfaultfd_ctx_cachep, ctx); > - } > return fd; This introduces the opposite bug: now it's hardcoded to *not* use O_CLOEXEC, instead of using the flag the user passed in the flags argument to the syscall. - Eric
