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nfsd: simplify fh_verify access checks 

All nfsd security depends on the security checks in fh_verify, and
especially on nfsd_setuser().

It therefore bothers me that the nfsd_setuser call may be made from
three different places, depending on whether the filehandle has already
been mapped to a dentry, and on whether subtreechecking is in force.

Instead, make an unconditional call in fh_verify(), so it's trivial to
verify that the call always occurs.

That leaves us with a redundant nfsd_setuser() call in the subtreecheck
case--it needs the correct user set earlier in order to check execute
permissions on the path to this filehandle--but I'm willing to accept
that minor inefficiency in the subtreecheck case in return for more
straightforward permission checking.

Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>
This commit is contained in:
J. Bruce Fields 2009-11-25 17:42:05 -05:00
parent 9b8b317d58
commit 864f0f61f8
1 changed files with 21 additions and 29 deletions
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50
fs/nfsd/nfsfh.c
View File

@ -233,14 +233,6 @@ static __be32 nfsd_set_fh_dentry(struct svc_rqst *rqstp, struct svc_fh *fhp)
goto out;
}
if (exp->ex_flags & NFSEXP_NOSUBTREECHECK) {
error = nfsd_setuser_and_check_port(rqstp, exp);
if (error) {
dput(dentry);
goto out;
}
}
if (S_ISDIR(dentry->d_inode->i_mode) &&
(dentry->d_flags & DCACHE_DISCONNECTED)) {
printk("nfsd: find_fh_dentry returned a DISCONNECTED directory: %s/%s\n",
@ -295,28 +287,28 @@ fh_verify(struct svc_rqst *rqstp, struct svc_fh *fhp, int type, int access)
error = nfsd_set_fh_dentry(rqstp, fhp);
if (error)
goto out;
dentry = fhp->fh_dentry;
exp = fhp->fh_export;
} else {
/*
* just rechecking permissions
* (e.g. nfsproc_create calls fh_verify, then nfsd_create
* does as well)
*/
dprintk("nfsd: fh_verify - just checking\n");
dentry = fhp->fh_dentry;
exp = fhp->fh_export;
/*
* Set user creds for this exportpoint; necessary even
* in the "just checking" case because this may be a
* filehandle that was created by fh_compose, and that
* is about to be used in another nfsv4 compound
* operation.
*/
error = nfsd_setuser_and_check_port(rqstp, exp);
if (error)
goto out;
}
dentry = fhp->fh_dentry;
exp = fhp->fh_export;
/*
* We still have to do all these permission checks, even when
* fh_dentry is already set:
* - fh_verify may be called multiple times with different
* "access" arguments (e.g. nfsd_proc_create calls
* fh_verify(...,NFSD_MAY_EXEC) first, then later (in
* nfsd_create) calls fh_verify(...,NFSD_MAY_CREATE).
* - in the NFSv4 case, the filehandle may have been filled
* in by fh_compose, and given a dentry, but further
* compound operations performed with that filehandle
* still need permissions checks. In the worst case, a
* mountpoint crossing may have changed the export
* options, and we may now need to use a different uid
* (for example, if different id-squashing options are in
* effect on the new filesystem).
*/
error = nfsd_setuser_and_check_port(rqstp, exp);
if (error)
goto out;
error = nfsd_mode_check(rqstp, dentry->d_inode->i_mode, type);
if (error)