[PATCH 5.4 082/203] afs: Fix use-after-loss-of-ref

Greg Kroah-Hartman
2020-01-16T23:46:10Z

From: David Howells <dhowells@redhat.com>

commit 40a708bd622b78582ae3d280de29b09b50bd04c0 upstream.

afs_lookup() has a tracepoint to indicate the outcome of
d_splice_alias(), passing it the inode to retrieve the fid from.
However, the function gave up its ref on that inode when it called
d_splice_alias(), which may have failed and dropped the inode.

Fix this by caching the fid.

Fixes: 80548b03991f ("afs: Add more tracepoints")
Reported-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
fs/afs/dir.c | 12 +++++++-----
include/trace/events/afs.h | 12 +++---------
2 files changed, 10 insertions(+), 14 deletions(-)

--- a/fs/afs/dir.c
+++ b/fs/afs/dir.c
@@ -908,6 +908,7 @@ static struct dentry *afs_lookup(struct
unsigned int flags)
{
struct afs_vnode *dvnode = AFS_FS_I(dir);
+ struct afs_fid fid = {};
struct inode *inode;
struct dentry *d;
struct key *key;
@@ -957,15 +958,16 @@ static struct dentry *afs_lookup(struct
dentry->d_fsdata =
(void *)(unsigned long)dvnode->status.data_version;
}
+
+ if (!IS_ERR_OR_NULL(inode))
+ fid = AFS_FS_I(inode)->fid;
+
d = d_splice_alias(inode, dentry);
if (!IS_ERR_OR_NULL(d)) {
d->d_fsdata = dentry->d_fsdata;
- trace_afs_lookup(dvnode, &d->d_name,
- inode ? AFS_FS_I(inode) : NULL);
+ trace_afs_lookup(dvnode, &d->d_name, &fid);
} else {
- trace_afs_lookup(dvnode, &dentry->d_name,
- IS_ERR_OR_NULL(inode) ? NULL
- : AFS_FS_I(inode));
+ trace_afs_lookup(dvnode, &dentry->d_name, &fid);
}
return d;
}
--- a/include/trace/events/afs.h
+++ b/include/trace/events/afs.h
@@ -915,9 +915,9 @@ TRACE_EVENT(afs_call_state,

TRACE_EVENT(afs_lookup,
TP_PROTO(struct afs_vnode *dvnode, const struct qstr *name,
- struct afs_vnode *vnode),
+ struct afs_fid *fid),

- TP_ARGS(dvnode, name, vnode),
+ TP_ARGS(dvnode, name, fid),

TP_STRUCT__entry(
__field_struct(struct afs_fid, dfid )
@@ -928,13 +928,7 @@ TRACE_EVENT(afs_lookup,
TP_fast_assign(
int __len = min_t(int, name->len, 23);
__entry->dfid = dvnode->fid;
- if (vnode) {
- __entry->fid = vnode->fid;
- } else {
- __entry->fid.vid = 0;
- __entry->fid.vnode = 0;
- __entry->fid.unique = 0;
- }
+ __entry->fid = *fid;
memcpy(__entry->name, name->name, __len);
__entry->name[__len] = 0;
),