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Don't allow VOP_GETEXTATTR to set uio->uio_offset != 0, as we don't

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provide locking over extended attribute operations, requiring that
individual operations be atomic.  Allowing non-zero starting offsets
permits applications/etc to put themselves at risk for inconsistent
behavior.  As VOP_SETEXTATTR already prohibited non-zero write offsets,
this makes sense.

Suggested by:	Andreas Gruenbacher <a.gruenbacher@bestbits.at>
This commit is contained in:
Robert Watson 2000-05-03 05:50:46 +00:00
parent 86a5a8c251
commit a7e8b37043
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=59913
1 changed files with 10 additions and 12 deletions
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22
sys/ufs/ufs/ufs_extattr.c
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@ -443,7 +443,7 @@ ufs_extattr_get(struct vnode *vp, char *name, struct uio *uio,
struct mount *mp = vp->v_mount;
struct ufsmount *ump = VFSTOUFS(mp);
struct inode *ip = VTOI(vp);
off_t base_offset, old_offset, offset;
off_t base_offset, offset;
size_t size, old_size;
int error = 0;
@ -459,10 +459,12 @@ ufs_extattr_get(struct vnode *vp, char *name, struct uio *uio,
return (error);
/*
* Early rejection of offsets that are invalid
* Allow only offsets of zero to encourage the read/replace
* extended attribute semantic. Otherwise we can't guarantee
* atomicity, as we don't provide locks for extended
* attributes.
*/
if (uio->uio_offset >= attribute->uele_fileheader.uef_size ||
uio->uio_offset < 0)
if (uio->uio_offset != 0)
return (ENXIO);
/*
@ -529,28 +531,24 @@ ufs_extattr_get(struct vnode *vp, char *name, struct uio *uio,
}
/* allow for offset into the attr data */
offset = base_offset + sizeof(struct ufs_extattr_header) +
uio->uio_offset;
uio->uio_offset = base_offset + sizeof(struct ufs_extattr_header);
/*
* Figure out maximum to transfer -- use buffer size and local data
* limit.
*/
size = MIN(uio->uio_resid, ueh.ueh_len - uio->uio_offset);
old_offset = uio->uio_offset;
uio->uio_offset = offset;
size = MIN(uio->uio_resid, ueh.ueh_len);
old_size = uio->uio_resid;
uio->uio_resid = size;
error = VOP_READ(attribute->uele_backing_vnode, uio, 0,
ump->um_extattr.uepm_ucred);
if (error) {
uio->uio_offset = old_offset;
uio->uio_offset = 0;
goto vopunlock_exit;
}
uio->uio_offset = old_offset;
uio->uio_offset = 0;
uio->uio_resid = old_size - (size - uio->uio_resid);
vopunlock_exit: