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vfs: add more safety against concurrent forced unmount to vn_write

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1. stop re-reading ->v_mount (can become NULL)
2. stop re-reading ->v_type (can change to VBAD)
This commit is contained in:
Mateusz Guzik 2021-05-14 13:26:56 +02:00
parent b5fb9ae687
commit ca1ce50b2b
1 changed files with 14 additions and 7 deletions
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21
sys/kern/vfs_vnops.c
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@ -1107,6 +1107,7 @@ vn_write(struct file *fp, struct uio *uio, struct ucred *active_cred, int flags,
off_t orig_offset;
int error, ioflag, lock_flags;
int advice;
bool need_finished_write;
KASSERT(uio->uio_td == td, ("uio_td %p is not td %p",
uio->uio_td, td));
@ -1121,9 +1122,11 @@ vn_write(struct file *fp, struct uio *uio, struct ucred *active_cred, int flags,
ioflag |= IO_NDELAY;
if (fp->f_flag & O_DIRECT)
ioflag |= IO_DIRECT;
if ((fp->f_flag & O_FSYNC) ||
(vp->v_mount && (vp->v_mount->mnt_flag & MNT_SYNCHRONOUS)))
ioflag |= IO_SYNC;
if (fp->f_flag & O_FSYNC) {
mp = atomic_load_ptr(&vp->v_mount);
if (mp != NULL && mp->mnt_flag & MNT_SYNCHRONOUS)
ioflag |= IO_SYNC;
}
/*
* For O_DSYNC we set both IO_SYNC and IO_DATASYNC, so that VOP_WRITE()
* implementations that don't understand IO_DATASYNC fall back to full
@ -1132,9 +1135,13 @@ vn_write(struct file *fp, struct uio *uio, struct ucred *active_cred, int flags,
if (fp->f_flag & O_DSYNC)
ioflag |= IO_SYNC | IO_DATASYNC;
mp = NULL;
if (vp->v_type != VCHR &&
(error = vn_start_write(vp, &mp, V_WAIT | PCATCH)) != 0)
goto unlock;
need_finished_write = false;
if (vp->v_type != VCHR) {
error = vn_start_write(vp, &mp, V_WAIT | PCATCH);
if (error != 0)
goto unlock;
need_finished_write = true;
}
advice = get_advice(fp, uio);
@ -1165,7 +1172,7 @@ vn_write(struct file *fp, struct uio *uio, struct ucred *active_cred, int flags,
error = VOP_WRITE(vp, uio, ioflag, fp->f_cred);
fp->f_nextoff[UIO_WRITE] = uio->uio_offset;
VOP_UNLOCK(vp);
if (vp->v_type != VCHR)
if (need_finished_write)
vn_finished_write(mp);
if (error == 0 && advice == POSIX_FADV_NOREUSE &&
orig_offset != uio->uio_offset)