| Message ID | 20200723171227.446711-4-mic@digikod.net (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Add support for O_MAYEXEC | expand |
Mickaël Salaün <mic@digikod.net> writes: > From: Kees Cook <keescook@chromium.org> > > The path_noexec() check, like the regular file check, was happening too > late, letting LSMs see impossible execve()s. Check it earlier as well > in may_open() and collect the redundant fs/exec.c path_noexec() test > under the same robustness comment as the S_ISREG() check. > > My notes on the call path, and related arguments, checks, etc: A big question arises, that I think someone already asked. Why perform this test in may_open directly instead of moving it into inode_permission. That way the code can be shared with faccessat, and any other code path that wants it? That would look to provide a more maintainable kernel. Eric > do_open_execat() > struct open_flags open_exec_flags = { > .open_flag = O_LARGEFILE | O_RDONLY | __FMODE_EXEC, > .acc_mode = MAY_EXEC, > ... > do_filp_open(dfd, filename, open_flags) > path_openat(nameidata, open_flags, flags) > file = alloc_empty_file(open_flags, current_cred()); > do_open(nameidata, file, open_flags) > may_open(path, acc_mode, open_flag) > /* new location of MAY_EXEC vs path_noexec() test */ > inode_permission(inode, MAY_OPEN | acc_mode) > security_inode_permission(inode, acc_mode) > vfs_open(path, file) > do_dentry_open(file, path->dentry->d_inode, open) > security_file_open(f) > open() > /* old location of path_noexec() test */ > > Signed-off-by: Mickaël Salaün <mic@digikod.net> > Signed-off-by: Kees Cook <keescook@chromium.org> > Link: https://lore.kernel.org/r/20200605160013.3954297-4-keescook@chromium.org > --- > fs/exec.c | 12 ++++-------- > fs/namei.c | 4 ++++ > 2 files changed, 8 insertions(+), 8 deletions(-) > > diff --git a/fs/exec.c b/fs/exec.c > index bdc6a6eb5dce..4eea20c27b01 100644 > --- a/fs/exec.c > +++ b/fs/exec.c > @@ -147,10 +147,8 @@ SYSCALL_DEFINE1(uselib, const char __user *, library) > * and check again at the very end too. > */ > error = -EACCES; > - if (WARN_ON_ONCE(!S_ISREG(file_inode(file)->i_mode))) > - goto exit; > - > - if (path_noexec(&file->f_path)) > + if (WARN_ON_ONCE(!S_ISREG(file_inode(file)->i_mode) || > + path_noexec(&file->f_path))) > goto exit; > > fsnotify_open(file); > @@ -897,10 +895,8 @@ static struct file *do_open_execat(int fd, struct filename *name, int flags) > * and check again at the very end too. > */ > err = -EACCES; > - if (WARN_ON_ONCE(!S_ISREG(file_inode(file)->i_mode))) > - goto exit; > - > - if (path_noexec(&file->f_path)) > + if (WARN_ON_ONCE(!S_ISREG(file_inode(file)->i_mode) || > + path_noexec(&file->f_path))) > goto exit; > > err = deny_write_access(file); > diff --git a/fs/namei.c b/fs/namei.c > index a559ad943970..ddc9b25540fe 100644 > --- a/fs/namei.c > +++ b/fs/namei.c > @@ -2863,6 +2863,10 @@ static int may_open(const struct path *path, int acc_mode, int flag) > return -EACCES; > flag &= ~O_TRUNC; > break; > + case S_IFREG: > + if ((acc_mode & MAY_EXEC) && path_noexec(path)) > + return -EACCES; > + break; > } > > error = inode_permission(inode, MAY_OPEN | acc_mode);
Kees Cook wrote this patch, which is in Andrew Morton's tree, but I think you're talking about O_MAYEXEC, not this patch specifically. On 11/08/2020 21:36, Eric W. Biederman wrote: > Mickaël Salaün <mic@digikod.net> writes: > >> From: Kees Cook <keescook@chromium.org> >> >> The path_noexec() check, like the regular file check, was happening too >> late, letting LSMs see impossible execve()s. Check it earlier as well >> in may_open() and collect the redundant fs/exec.c path_noexec() test >> under the same robustness comment as the S_ISREG() check. >> >> My notes on the call path, and related arguments, checks, etc: > > A big question arises, that I think someone already asked. Al Viro and Jann Horn expressed such concerns for O_MAYEXEC: https://lore.kernel.org/lkml/0cc94c91-afd3-27cd-b831-8ea16ca8ca93@digikod.net/ > > Why perform this test in may_open directly instead of moving > it into inode_permission. That way the code can be shared with > faccessat, and any other code path that wants it? This patch is just a refactoring. About O_MAYEXEC, path-based LSM, IMA and IPE need to work on a struct file, whereas inode_permission() only gives a struct inode. However, faccessat2(2) (with extended flags) seems to be the perfect candidate if we want to be able to check file descriptors. > > That would look to provide a more maintainable kernel. Why would it be more maintainable? > > Eric > > >> do_open_execat() >> struct open_flags open_exec_flags = { >> .open_flag = O_LARGEFILE | O_RDONLY | __FMODE_EXEC, >> .acc_mode = MAY_EXEC, >> ... >> do_filp_open(dfd, filename, open_flags) >> path_openat(nameidata, open_flags, flags) >> file = alloc_empty_file(open_flags, current_cred()); >> do_open(nameidata, file, open_flags) >> may_open(path, acc_mode, open_flag) >> /* new location of MAY_EXEC vs path_noexec() test */ >> inode_permission(inode, MAY_OPEN | acc_mode) >> security_inode_permission(inode, acc_mode) >> vfs_open(path, file) >> do_dentry_open(file, path->dentry->d_inode, open) >> security_file_open(f) >> open() >> /* old location of path_noexec() test */ >> >> Signed-off-by: Mickaël Salaün <mic@digikod.net> >> Signed-off-by: Kees Cook <keescook@chromium.org> >> Link: https://lore.kernel.org/r/20200605160013.3954297-4-keescook@chromium.org >> --- >> fs/exec.c | 12 ++++-------- >> fs/namei.c | 4 ++++ >> 2 files changed, 8 insertions(+), 8 deletions(-) >> >> diff --git a/fs/exec.c b/fs/exec.c >> index bdc6a6eb5dce..4eea20c27b01 100644 >> --- a/fs/exec.c >> +++ b/fs/exec.c >> @@ -147,10 +147,8 @@ SYSCALL_DEFINE1(uselib, const char __user *, library) >> * and check again at the very end too. >> */ >> error = -EACCES; >> - if (WARN_ON_ONCE(!S_ISREG(file_inode(file)->i_mode))) >> - goto exit; >> - >> - if (path_noexec(&file->f_path)) >> + if (WARN_ON_ONCE(!S_ISREG(file_inode(file)->i_mode) || >> + path_noexec(&file->f_path))) >> goto exit; >> >> fsnotify_open(file); >> @@ -897,10 +895,8 @@ static struct file *do_open_execat(int fd, struct filename *name, int flags) >> * and check again at the very end too. >> */ >> err = -EACCES; >> - if (WARN_ON_ONCE(!S_ISREG(file_inode(file)->i_mode))) >> - goto exit; >> - >> - if (path_noexec(&file->f_path)) >> + if (WARN_ON_ONCE(!S_ISREG(file_inode(file)->i_mode) || >> + path_noexec(&file->f_path))) >> goto exit; >> >> err = deny_write_access(file); >> diff --git a/fs/namei.c b/fs/namei.c >> index a559ad943970..ddc9b25540fe 100644 >> --- a/fs/namei.c >> +++ b/fs/namei.c >> @@ -2863,6 +2863,10 @@ static int may_open(const struct path *path, int acc_mode, int flag) >> return -EACCES; >> flag &= ~O_TRUNC; >> break; >> + case S_IFREG: >> + if ((acc_mode & MAY_EXEC) && path_noexec(path)) >> + return -EACCES; >> + break; >> } >> >> error = inode_permission(inode, MAY_OPEN | acc_mode);
diff --git a/fs/exec.c b/fs/exec.c index bdc6a6eb5dce..4eea20c27b01 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -147,10 +147,8 @@ SYSCALL_DEFINE1(uselib, const char __user *, library) * and check again at the very end too. */ error = -EACCES; - if (WARN_ON_ONCE(!S_ISREG(file_inode(file)->i_mode))) - goto exit; - - if (path_noexec(&file->f_path)) + if (WARN_ON_ONCE(!S_ISREG(file_inode(file)->i_mode) || + path_noexec(&file->f_path))) goto exit; fsnotify_open(file); @@ -897,10 +895,8 @@ static struct file *do_open_execat(int fd, struct filename *name, int flags) * and check again at the very end too. */ err = -EACCES; - if (WARN_ON_ONCE(!S_ISREG(file_inode(file)->i_mode))) - goto exit; - - if (path_noexec(&file->f_path)) + if (WARN_ON_ONCE(!S_ISREG(file_inode(file)->i_mode) || + path_noexec(&file->f_path))) goto exit; err = deny_write_access(file); diff --git a/fs/namei.c b/fs/namei.c index a559ad943970..ddc9b25540fe 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -2863,6 +2863,10 @@ static int may_open(const struct path *path, int acc_mode, int flag) return -EACCES; flag &= ~O_TRUNC; break; + case S_IFREG: + if ((acc_mode & MAY_EXEC) && path_noexec(path)) + return -EACCES; + break; } error = inode_permission(inode, MAY_OPEN | acc_mode);