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Fix an issue with executing tmpfs binary.

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Suppose that a binary was executed from tmpfs mount, and the text
vnode was reclaimed while the binary was still running.  It is
possible during even the normal operations since tmpfs vnode'
vm_object has swap type, and no references on the vnode is held.  Also
assume that the text vnode was revived for some reason.  Then, on the
process exit or exec, unmapping of the text mapping tries to remove
the text reference from the vnode, but since it went from
recycle/instantiation cycle, there is no reference kept, and assertion
in VOP_UNSET_TEXT_CHECKED() triggers.

Fix this by keeping a use reference on the tmpfs vnode for each exec
reference.  This prevents the vnode reclamation while executable map
entry is active.

Do it by adding per-mount flag MNTK_TEXT_REFS that directs
vop_stdset_text() to add use ref on first vnode text use, and
per-vnode VI_TEXT_REF flag, to record the need on unref in
vop_stdunset_text() on last vnode text use going away.  Set
MNTK_TEXT_REFS for tmpfs mounts.

Reported by:	bdrewery
Tested by:	sbruno, pho (previous version)
Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
This commit is contained in:
Konstantin Belousov 2019-08-18 20:36:11 +00:00
parent bb9e2184f0
commit de4e1aeb21
4 changed files with 25 additions and 1 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

3
sys/fs/tmpfs/tmpfs_vfsops.c
View File

@ -507,7 +507,8 @@ tmpfs_mount(struct mount *mp)
MNT_ILOCK(mp);
mp->mnt_flag |= MNT_LOCAL;
mp->mnt_kern_flag |= MNTK_LOOKUP_SHARED | MNTK_EXTENDED_SHARED;
mp->mnt_kern_flag |= MNTK_LOOKUP_SHARED | MNTK_EXTENDED_SHARED |
MNTK_TEXT_REFS;
MNT_IUNLOCK(mp);
mp->mnt_data = tmp;

21
sys/kern/vfs_default.c
View File

@ -1082,6 +1082,7 @@ int
vop_stdset_text(struct vop_set_text_args *ap)
{
struct vnode *vp;
struct mount *mp;
int error;
vp = ap->a_vp;
@ -1089,6 +1090,17 @@ vop_stdset_text(struct vop_set_text_args *ap)
if (vp->v_writecount > 0) {
error = ETXTBSY;
} else {
/*
* If requested by fs, keep a use reference to the
* vnode until the last text reference is released.
*/
mp = vp->v_mount;
if (mp != NULL && (mp->mnt_kern_flag & MNTK_TEXT_REFS) != 0 &&
vp->v_writecount == 0) {
vp->v_iflag |= VI_TEXT_REF;
vrefl(vp);
}
vp->v_writecount--;
error = 0;
}
@ -1101,16 +1113,25 @@ vop_stdunset_text(struct vop_unset_text_args *ap)
{
struct vnode *vp;
int error;
bool last;
vp = ap->a_vp;
last = false;
VI_LOCK(vp);
if (vp->v_writecount < 0) {
if ((vp->v_iflag & VI_TEXT_REF) != 0 &&
vp->v_writecount == -1) {
last = true;
vp->v_iflag &= ~VI_TEXT_REF;
}
vp->v_writecount++;
error = 0;
} else {
error = EINVAL;
}
VI_UNLOCK(vp);
if (last)
vunref(vp);
return (error);
}

1
sys/sys/mount.h
View File

@ -398,6 +398,7 @@ void __mnt_vnode_markerfree_active(struct vnode **mvp, struct mount *);
#define MNTK_MARKER 0x00001000
#define MNTK_UNMAPPED_BUFS 0x00002000
#define MNTK_USES_BCACHE 0x00004000 /* FS uses the buffer cache. */
#define MNTK_TEXT_REFS 0x00008000 /* Keep use ref for text */
#define MNTK_NOASYNC 0x00800000 /* disable async */
#define MNTK_UNMOUNT 0x01000000 /* unmount in progress */
#define MNTK_MWAIT 0x02000000 /* waiting for unmount to finish */

1
sys/sys/vnode.h
View File

@ -233,6 +233,7 @@ struct xvnode {
* VI_DOOMED is doubly protected by the interlock and vnode lock. Both
* are required for writing but the status may be checked with either.
*/
#define VI_TEXT_REF 0x0001 /* Text ref grabbed use ref */
#define VI_MOUNT 0x0020 /* Mount in progress */
#define VI_DOOMED 0x0080 /* This vnode is being recycled */
#define VI_FREE 0x0100 /* This vnode is on the freelist */