| Message ID | 87eepe6x7p.fsf@x220.int.ebiederm.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Implementing kernel_execve | expand |
On Tue, Jul 14, 2020 at 08:30:02AM -0500, Eric W. Biederman wrote: > > Currently it is necessary for the usermode helper code and the code that > launches init to use set_fs so that pages coming from the kernel look like > they are coming from userspace. > > To allow that usage of set_fs to be removed cleanly the argument copying > from userspace needs to happen earlier. Move the allocation and > initialization of bprm->mm into alloc_bprm so that the bprm->mm is > available early to store the new user stack into. This is a prerequisite > for copying argv and envp into the new user stack early before ther rest of > exec. > > To keep the things consistent the cleanup of bprm->mm is moved into > free_bprm. So that bprm->mm will be cleaned up whenever bprm->mm is > allocated and free_bprm are called. > > Moving bprm_mm_init earlier is safe as it does not depend on any files, > current->in_execve, current->fs->in_exec, bprm->unsafe, or the if the file > table is shared. (AKA bprm_mm_init does not depend on any of the code that > happens between alloc_bprm and where it was previously called.) > > This moves bprm->mm cleanup after current->fs->in_exec is set to 0. This > is safe because current->fs->in_exec is only used to preventy taking an > additional reference on the fs_struct. > > This moves bprm->mm cleanup after current->in_execve is set to 0. This is > safe because current->in_execve is only used by the lsms (apparmor and > tomoyou) and always for LSM specific functions, never for anything to do > with the mm. > > This adds bprm->mm cleanup into the successful return path. This is safe > because being on the successful return path implies that begin_new_exec > succeeded and set brpm->mm to NULL. As bprm->mm is NULL bprm cleanup I am > moving into free_bprm will do nothing. > > Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com> Reviewed-by: Kees Cook <keescook@chromium.org> This looks correct, and is required before moving the arg pages stuff, so good. :)
On Tue, Jul 14, 2020 at 08:30:02AM -0500, Eric W. Biederman wrote: > > Currently it is necessary for the usermode helper code and the code that > launches init to use set_fs so that pages coming from the kernel look like > they are coming from userspace. > > To allow that usage of set_fs to be removed cleanly the argument copying > from userspace needs to happen earlier. Move the allocation and > initialization of bprm->mm into alloc_bprm so that the bprm->mm is > available early to store the new user stack into. This is a prerequisite > for copying argv and envp into the new user stack early before ther rest of > exec. > > To keep the things consistent the cleanup of bprm->mm is moved into > free_bprm. So that bprm->mm will be cleaned up whenever bprm->mm is > allocated and free_bprm are called. > > Moving bprm_mm_init earlier is safe as it does not depend on any files, > current->in_execve, current->fs->in_exec, bprm->unsafe, or the if the file > table is shared. (AKA bprm_mm_init does not depend on any of the code that > happens between alloc_bprm and where it was previously called.) > > This moves bprm->mm cleanup after current->fs->in_exec is set to 0. This > is safe because current->fs->in_exec is only used to preventy taking an > additional reference on the fs_struct. > > This moves bprm->mm cleanup after current->in_execve is set to 0. This is > safe because current->in_execve is only used by the lsms (apparmor and > tomoyou) and always for LSM specific functions, never for anything to do > with the mm. > > This adds bprm->mm cleanup into the successful return path. This is safe > because being on the successful return path implies that begin_new_exec > succeeded and set brpm->mm to NULL. As bprm->mm is NULL bprm cleanup I am > moving into free_bprm will do nothing. > > Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com> Looks good, Reviewed-by: Christoph Hellwig <hch@lst.de>
diff --git a/fs/exec.c b/fs/exec.c index 7e8af27dd199..afb168bf5e23 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -1543,6 +1543,10 @@ static int prepare_bprm_creds(struct linux_binprm *bprm) static void free_bprm(struct linux_binprm *bprm) { + if (bprm->mm) { + acct_arg_size(bprm, 0); + mmput(bprm->mm); + } free_arg_pages(bprm); if (bprm->cred) { mutex_unlock(¤t->signal->cred_guard_mutex); @@ -1582,6 +1586,10 @@ static struct linux_binprm *alloc_bprm(int fd, struct filename *filename) bprm->filename = bprm->fdpath; } bprm->interp = bprm->filename; + + retval = bprm_mm_init(bprm); + if (retval) + goto out_free; return bprm; out_free: @@ -1911,10 +1919,6 @@ static int do_execveat_common(int fd, struct filename *filename, close_on_exec(fd, rcu_dereference_raw(current->files->fdt))) bprm->interp_flags |= BINPRM_FLAGS_PATH_INACCESSIBLE; - retval = bprm_mm_init(bprm); - if (retval) - goto out_unmark; - retval = prepare_arg_pages(bprm, argv, envp); if (retval < 0) goto out; @@ -1962,10 +1966,6 @@ static int do_execveat_common(int fd, struct filename *filename, */ if (bprm->point_of_no_return && !fatal_signal_pending(current)) force_sigsegv(SIGSEGV); - if (bprm->mm) { - acct_arg_size(bprm, 0); - mmput(bprm->mm); - } out_unmark: current->fs->in_exec = 0;
Currently it is necessary for the usermode helper code and the code that launches init to use set_fs so that pages coming from the kernel look like they are coming from userspace. To allow that usage of set_fs to be removed cleanly the argument copying from userspace needs to happen earlier. Move the allocation and initialization of bprm->mm into alloc_bprm so that the bprm->mm is available early to store the new user stack into. This is a prerequisite for copying argv and envp into the new user stack early before ther rest of exec. To keep the things consistent the cleanup of bprm->mm is moved into free_bprm. So that bprm->mm will be cleaned up whenever bprm->mm is allocated and free_bprm are called. Moving bprm_mm_init earlier is safe as it does not depend on any files, current->in_execve, current->fs->in_exec, bprm->unsafe, or the if the file table is shared. (AKA bprm_mm_init does not depend on any of the code that happens between alloc_bprm and where it was previously called.) This moves bprm->mm cleanup after current->fs->in_exec is set to 0. This is safe because current->fs->in_exec is only used to preventy taking an additional reference on the fs_struct. This moves bprm->mm cleanup after current->in_execve is set to 0. This is safe because current->in_execve is only used by the lsms (apparmor and tomoyou) and always for LSM specific functions, never for anything to do with the mm. This adds bprm->mm cleanup into the successful return path. This is safe because being on the successful return path implies that begin_new_exec succeeded and set brpm->mm to NULL. As bprm->mm is NULL bprm cleanup I am moving into free_bprm will do nothing. Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com> --- fs/exec.c | 16 ++++++++-------- 1 file changed, 8 insertions(+), 8 deletions(-)