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posixshm: start counting writeable mappings

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r351650 switched posixshm to using OBJT_SWAP for shm_object

r351795 added support to the swap_pager for tracking writeable mappings

Take advantage of this and start tracking writeable mappings; fd sealing
will use this to reject a seal on writing with EBUSY if any such mapping
exist.

Reviewed by:	kib, markj
Differential Revision:	https://reviews.freebsd.org/D21456
This commit is contained in:
Kyle Evans 2019-09-03 20:33:38 +00:00
parent fe7bcbaf50
commit dca52ab480
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=351796
1 changed files with 12 additions and 5 deletions
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17
sys/kern/uipc_shm.c
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@ -895,6 +895,7 @@ shm_mmap(struct file *fp, vm_map_t map, vm_offset_t *addr, vm_size_t objsize,
struct shmfd *shmfd;
vm_prot_t maxprot;
int error;
bool writecnt;
shmfd = fp->f_data;
maxprot = VM_PROT_NONE;
@ -905,10 +906,10 @@ shm_mmap(struct file *fp, vm_map_t map, vm_offset_t *addr, vm_size_t objsize,
if ((fp->f_flag & FWRITE) != 0)
maxprot |= VM_PROT_WRITE;
writecnt = (flags & MAP_SHARED) != 0 && (prot & VM_PROT_WRITE) != 0;
/* Don't permit shared writable mappings on read-only descriptors. */
if ((flags & MAP_SHARED) != 0 &&
(maxprot & VM_PROT_WRITE) == 0 &&
(prot & VM_PROT_WRITE) != 0)
if (writecnt && (maxprot & VM_PROT_WRITE) == 0)
return (EACCES);
maxprot &= cap_maxprot;
@ -931,10 +932,16 @@ shm_mmap(struct file *fp, vm_map_t map, vm_offset_t *addr, vm_size_t objsize,
mtx_unlock(&shm_timestamp_lock);
vm_object_reference(shmfd->shm_object);
if (writecnt)
vm_pager_update_writecount(shmfd->shm_object, 0, objsize);
error = vm_mmap_object(map, addr, objsize, prot, maxprot, flags,
shmfd->shm_object, foff, FALSE, td);
if (error != 0)
shmfd->shm_object, foff, writecnt, td);
if (error != 0) {
if (writecnt)
vm_pager_release_writecount(shmfd->shm_object, 0,
objsize);
vm_object_deallocate(shmfd->shm_object);
}
return (error);
}