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afs: Fix use-after-loss-of-ref 

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: 80548b0399 ("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>
This commit is contained in:
David Howells 2020-01-14 16:16:25 +00:00 committed by Linus Torvalds
parent 8379bb84be
commit 40a708bd62
2 changed files with 10 additions and 14 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

12
fs/afs/dir.c
View File

@ -908,6 +908,7 @@ static struct dentry *afs_lookup(struct inode *dir, struct dentry *dentry,
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 inode *dir, struct dentry *dentry,
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;
}

12
include/trace/events/afs.h
View File

@ -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;
),