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pidfs: add pidfs_dentry_open() helper

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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) <brauner@kernel.org>
This commit is contained in:
Christian Brauner 2026-07-22 13:56:28 +02:00
parent 172ed6c2b6
commit 927b89700e
1 changed files with 21 additions and 21 deletions
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42
fs/pidfs.c
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@ -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)