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linux(4) clone(2): Correctly handle CLONE_FS and CLONE_FILES

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The two flags are distinct and it is impossible to correctly handle clone(2)
without the assistance of fork1().  This change depends on the pwddesc split
introduced in r367777.

I've added a fork_req flag, FR2_SHARE_PATHS, which indicates that p_pd
should be treated the opposite way p_fd is (based on RFFDG flag).  This is a
little ugly, but the benefit is that existing RFFDG API is preserved.
Holding FR2_SHARE_PATHS disabled, RFFDG indicates both p_fd and p_pd are
copied, while !RFFDG indicates both should be cloned.

In Chrome, clone(2) is used with CLONE_FS, without CLONE_FILES, and expects
independent fd tables.

The previous conflation of CLONE_FS and CLONE_FILES was introduced in
r163371 (2006).

Discussed with:	markj, trasz (earlier version)
Differential Revision:	https://reviews.freebsd.org/D27016
This commit is contained in:
cem 2020-11-17 21:20:11 +00:00
parent f0d3db347b
commit 10dd999b1b
3 changed files with 20 additions and 11 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

18
sys/compat/linux/linux_fork.c
View File

@ -131,12 +131,13 @@ static int
linux_clone_proc(struct thread *td, struct linux_clone_args *args)
{
struct fork_req fr;
int error, ff = RFPROC | RFSTOPPED;
int error, ff = RFPROC | RFSTOPPED, f2;
struct proc *p2;
struct thread *td2;
int exit_signal;
struct linux_emuldata *em;
f2 = 0;
exit_signal = args->flags & 0x000000ff;
if (LINUX_SIG_VALID(exit_signal)) {
exit_signal = linux_to_bsd_signal(exit_signal);
@ -147,14 +148,14 @@ linux_clone_proc(struct thread *td, struct linux_clone_args *args)
ff |= RFMEM;
if (args->flags & LINUX_CLONE_SIGHAND)
ff |= RFSIGSHARE;
/*
* XXX: In Linux, sharing of fs info (chroot/cwd/umask)
* and open files is independent. In FreeBSD, its in one
* structure but in reality it does not cause any problems
* because both of these flags are usually set together.
*/
if (!(args->flags & (LINUX_CLONE_FILES | LINUX_CLONE_FS)))
if (args->flags & LINUX_CLONE_FILES) {
if (!(args->flags & LINUX_CLONE_FS))
f2 |= FR2_SHARE_PATHS;
} else {
ff |= RFFDG;
if (args->flags & LINUX_CLONE_FS)
f2 |= FR2_SHARE_PATHS;
}
if (args->flags & LINUX_CLONE_PARENT_SETTID)
if (args->parent_tidptr == NULL)
@ -165,6 +166,7 @@ linux_clone_proc(struct thread *td, struct linux_clone_args *args)
bzero(&fr, sizeof(fr));
fr.fr_flags = ff;
fr.fr_flags2 = f2;
fr.fr_procp = &p2;
error = fork1(td, &fr);
if (error)

10
sys/kern/kern_fork.c
View File

@ -414,11 +414,17 @@ do_fork(struct thread *td, struct fork_req *fr, struct proc *p2, struct thread *
fd = fdinit(p1->p_fd, false, NULL);
fdtol = NULL;
} else if (fr->fr_flags & RFFDG) {
pd = pdcopy(p1->p_pd);
if (fr->fr_flags2 & FR2_SHARE_PATHS)
pd = pdshare(p1->p_pd);
else
pd = pdcopy(p1->p_pd);
fd = fdcopy(p1->p_fd);
fdtol = NULL;
} else {
pd = pdshare(p1->p_pd);
if (fr->fr_flags2 & FR2_SHARE_PATHS)
pd = pdcopy(p1->p_pd);
else
pd = pdshare(p1->p_pd);
fd = fdshare(p1->p_fd);
if (p1->p_fdtol == NULL)
p1->p_fdtol = filedesc_to_leader_alloc(NULL, NULL,

3
sys/sys/proc.h
View File

@ -1017,7 +1017,8 @@ struct fork_req {
int fr_pd_flags;
struct filecaps *fr_pd_fcaps;
int fr_flags2;
#define FR2_DROPSIG_CAUGHT 0x00001 /* Drop caught non-DFL signals */
#define FR2_DROPSIG_CAUGHT 0x00000001 /* Drop caught non-DFL signals */
#define FR2_SHARE_PATHS 0x00000002 /* Invert sense of RFFDG for paths */
};
/*