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FBSD: Use user creds for afs_vop_putpages()

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Currently, the FBSD afs_vop_putpages uses the credentials of the
current process for writing data back to the fileserver. Usually this
works, but sometimes we're being called from syncer(4), which runs as
root instead of as the user accessing the relevant file.

This means that instead of using the tokens from the user that wrote
to the relevant file, we use whatever tokens belong to uid 0. This
usually causes an EACCES error when trying to write the data back to
the fileserver, causing us to store EACCES (13) in avc->vc_error, and
possibly causing a message in the kernel log like so:

    afs: failed to store file (0/13)

Since we set vc_error during these errors, this can also cause access
to the file to fail for the normal user process until vc_error is
cleared (such as when the file is closed).

To avoid this, store the credentials of the current user that
successfully opens the file for writing (in avc->cred), and use those
creds for writing back data to the fileserver. This is the same
approach that LINUX uses as of commit 70c8deab (Use user credentials
for Linux writepage()), and the NFS client code in FreeBSD itself (see
the usage of n_writecred in struct nfsnode as of 12.1-RELEASE).

Change-Id: I592d709b68d746bbdb326dfd7d012d6de829b905
Reviewed-on: https://gerrit.openafs.org/14164
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
This commit is contained in:
Andrew Deason 2020-04-26 00:25:10 -05:00 committed by Benjamin Kaduk
parent fe64ddd3b4
commit c3702afa8c
3 changed files with 29 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

27
src/afs/FBSD/osi_vnodeops.c
View File

@ -386,6 +386,14 @@ afs_vop_close(ap)
else
code = afs_close(avc, ap->a_fflag, afs_osi_credp);
osi_FlushPages(avc, ap->a_cred); /* hold GLOCK, but not basic vnode lock */
ObtainWriteLock(&avc->lock, 808);
if (avc->cred != NULL) {
crfree(avc->cred);
avc->cred = NULL;
}
ReleaseWriteLock(&avc->lock);
AFS_GUNLOCK();
return code;
}
@ -695,6 +703,7 @@ afs_vop_putpages(struct vop_putpages_args *ap)
vm_offset_t kva;
struct vnode *vp;
struct vcache *avc;
struct ucred *cred;
memset(&uio, 0, sizeof(uio));
memset(&iov, 0, sizeof(iov));
@ -736,7 +745,22 @@ afs_vop_putpages(struct vop_putpages_args *ap)
* sync |= IO_INVAL; */
AFS_GLOCK();
code = afs_write(avc, &uio, sync, osi_curcred(), 0);
ObtainReadLock(&avc->lock);
if (avc->cred != NULL) {
/*
* Use the creds from the process that opened this file for writing; if
* any. Otherwise, if we use the current process's creds, we may use
* the creds for uid 0 if we are writing back pages from the syncer(4)
* process.
*/
cred = crhold(avc->cred);
} else {
cred = crhold(curthread->td_ucred);
}
ReleaseReadLock(&avc->lock);
code = afs_write(avc, &uio, sync, cred, 0);
AFS_GUNLOCK();
pmap_qremove(kva, npages);
@ -751,6 +775,7 @@ afs_vop_putpages(struct vop_putpages_args *ap)
}
AFS_VM_OBJECT_WUNLOCK(vp->v_object);
}
crfree(cred);
return ap->a_rtvals[0];
}

2
src/afs/VNOPS/afs_vnop_open.c
View File

@ -151,7 +151,7 @@ afs_open(struct vcache **avcp, afs_int32 aflags, afs_ucred_t *acred)
if (writing)
tvc->execsOrWriters++;
tvc->opens++;
#if defined(AFS_SGI_ENV) || defined (AFS_LINUX_ENV)
#if defined(AFS_SGI_ENV) || defined (AFS_LINUX_ENV) || defined(AFS_FBSD_ENV)
if (writing && tvc->cred == NULL) {
crhold(acred);
tvc->cred = acred;

4
src/afs/afs.h
View File

@ -969,8 +969,8 @@ struct vcache {
struct bhv_desc vc_bhv_desc; /* vnode's behavior data. */
#endif
#endif /* AFS_SGI_ENV */
#if defined(AFS_LINUX_ENV)
cred_t *cred; /* last writer's cred */
#if defined(AFS_LINUX_ENV) || defined(AFS_FBSD_ENV)
afs_ucred_t *cred; /* last writer's cred */
#endif
#ifdef AFS_LINUX_ENV
struct dentry *target_link; /* dentry we prefer, when we are redirecting