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kern_shm_open: push O_CLOEXEC into caller control

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The motivation for this change is to allow wrappers around shm to be written
that don't set CLOEXEC. kern_shm_open currently accepts O_CLOEXEC but sets
it unconditionally. kern_shm_open is used by the shm_open(2) syscall, which
is mandated by POSIX to set CLOEXEC, and CloudABI's sys_fd_create1().
Presumably O_CLOEXEC is intended in the latter caller, but it's unclear from
the context.

sys_shm_open() now unconditionally sets O_CLOEXEC to meet POSIX
requirements, and a comment has been dropped in to kern_fd_open() to explain
the situation and add a pointer to where O_CLOEXEC setting is maintained for
shm_open(2) correctness. CloudABI's sys_fd_create1() also unconditionally
sets O_CLOEXEC to match previous behavior.

This also has the side-effect of making flags correctly reflect the
O_CLOEXEC status on this fd for the rest of kern_shm_open(), but a
glance-over leads me to believe that it didn't really matter.

Reviewed by:	kib, markj
MFC after:	1 week
Differential Revision:	https://reviews.freebsd.org/D21119
This commit is contained in:
Kyle Evans 2019-07-31 15:16:51 +00:00
parent 43ded0a321
commit b5a7ac997f
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=350464
2 changed files with 12 additions and 3 deletions
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3
sys/compat/cloudabi/cloudabi_fd.c
View file

@ -94,7 +94,8 @@ cloudabi_sys_fd_create1(struct thread *td,
case CLOUDABI_FILETYPE_SHARED_MEMORY:
cap_rights_init(&fcaps.fc_rights, CAP_FSTAT, CAP_FTRUNCATE,
CAP_MMAP_RWX);
return (kern_shm_open(td, SHM_ANON, O_RDWR, 0, &fcaps));
return (kern_shm_open(td, SHM_ANON, O_RDWR | O_CLOEXEC, 0,
&fcaps));
default:
return (EINVAL);
}

12
sys/kern/uipc_shm.c
View file

@ -729,7 +729,14 @@ kern_shm_open(struct thread *td, const char *userpath, int flags, mode_t mode,
fdp = td->td_proc->p_fd;
cmode = (mode & ~fdp->fd_cmask) & ACCESSPERMS;
error = falloc_caps(td, &fp, &fd, O_CLOEXEC, fcaps);
/*
* shm_open(2) created shm should always have O_CLOEXEC set, as mandated
* by POSIX. We allow it to be unset here so that an in-kernel
* interface may be written as a thin layer around shm, optionally not
* setting CLOEXEC. For shm_open(2), O_CLOEXEC is set unconditionally
* in sys_shm_open() to keep this implementation compliant.
*/
error = falloc_caps(td, &fp, &fd, flags & O_CLOEXEC, fcaps);
if (error)
return (error);
@ -844,7 +851,8 @@ int
sys_shm_open(struct thread *td, struct shm_open_args *uap)
{
return (kern_shm_open(td, uap->path, uap->flags, uap->mode, NULL));
return (kern_shm_open(td, uap->path, uap->flags | O_CLOEXEC, uap->mode,
NULL));
}
int