From 927b89700e9fdba61902f8828dbf9b5f29f40ea7 Mon Sep 17 00:00:00 2001 From: Christian Brauner Date: Wed, 22 Jul 2026 13:56:28 +0200 Subject: [PATCH] pidfs: add pidfs_dentry_open() helper Both pidfs_alloc_file() and pidfs_export_open() need to force O_RDWR and reapply the pidfd flags that do_dentry_open() strips. Move the common logic into a helper. PIDFD_AUTOKILL is now part of the restore mask in the file handle path as well, but pidfs_export_permission() rejects O_TRUNC, so this is a no-op there. But warn nonetheless. Link: https://patch.msgid.link/20260722-esszimmer-umsetzen-nennt-ed5fc604300a@brauner Signed-off-by: Christian Brauner (Amutable) --- fs/pidfs.c | 42 +++++++++++++++++++++--------------------- 1 file changed, 21 insertions(+), 21 deletions(-) diff --git a/fs/pidfs.c b/fs/pidfs.c index c20ffd747ff5..695215aa2a58 100644 --- a/fs/pidfs.c +++ b/fs/pidfs.c @@ -915,6 +915,20 @@ static struct dentry *pidfs_fh_to_dentry(struct super_block *sb, return path.dentry; } +static struct file *pidfs_dentry_open(const struct path *path, + unsigned int flags, + const struct cred *cred) +{ + struct file *file; + + /* pidfds are always O_RDWR. */ + file = dentry_open(path, flags | O_RDWR, cred); + /* do_dentry_open() strips O_EXCL and O_TRUNC. */ + if (!IS_ERR(file)) + file->f_flags |= flags & (PIDFD_THREAD | PIDFD_AUTOKILL); + return file; +} + /* * Make sure that we reject any nonsensical flags that users pass via * open_by_handle_at(). Note that PIDFD_THREAD is defined as O_EXCL, and @@ -939,18 +953,14 @@ static int pidfs_export_permission(struct handle_to_path_ctx *ctx, static struct file *pidfs_export_open(const struct path *path, unsigned int oflags) { - struct file *file; - /* - * Clear O_LARGEFILE as open_by_handle_at() forces it and raise - * O_RDWR as pidfds always are. + * Opening via file handle may never raise PIDFD_AUTOKILL. That can + * only be done at task creation! */ - oflags &= ~O_LARGEFILE; - file = dentry_open(path, oflags | O_RDWR, current_cred()); - /* do_dentry_open() strips O_EXCL, which encodes PIDFD_THREAD. */ - if (!IS_ERR(file)) - file->f_flags |= oflags & PIDFD_THREAD; - return file; + if (WARN_ON_ONCE(oflags & PIDFD_AUTOKILL)) + return ERR_PTR(-EINVAL); + /* Clear O_LARGEFILE as open_by_handle_at() forces it. */ + return pidfs_dentry_open(path, oflags & ~O_LARGEFILE, current_cred()); } static const struct export_operations pidfs_export_operations = { @@ -1114,7 +1124,6 @@ static struct file_system_type pidfs_type = { struct file *pidfs_alloc_file(struct pid *pid, unsigned int flags) { - struct file *pidfd_file; struct path path __free(path_put) = {}; int ret; @@ -1132,16 +1141,7 @@ struct file *pidfs_alloc_file(struct pid *pid, unsigned int flags) VFS_WARN_ON_ONCE(!pid->attr); flags &= ~PIDFD_STALE; - flags |= O_RDWR; - pidfd_file = dentry_open(&path, flags, current_cred()); - /* - * Raise PIDFD_THREAD and PIDFD_AUTOKILL explicitly as - * do_dentry_open() strips O_EXCL and O_TRUNC. - */ - if (!IS_ERR(pidfd_file)) - pidfd_file->f_flags |= (flags & (PIDFD_THREAD | PIDFD_AUTOKILL)); - - return pidfd_file; + return pidfs_dentry_open(&path, flags, current_cred()); } void __init pidfs_init(void)