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@xxxxxxxxxxx> writes: > >> From: Kees Cook <keescook@xxxxxxxxxxxx> >> >> 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@xxxxxxxxxxx/ > > 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@xxxxxxxxxxx> >> Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx> >> Link: https://lore.kernel.org/r/20200605160013.3954297-4-keescook@xxxxxxxxxxxx >> --- >> 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);
