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nfsd: Cap case-folding probe cost across READDIR entries

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NFSv4 READDIR carries a per-entry attrmask. When the attrmask
includes FATTR4_CASE_INSENSITIVE or FATTR4_CASE_PRESERVING,
nfsd4_encode_fattr4() resolves each non-directory child's case
attributes by calling nfsd_get_case_info(), which dget_parent()s
back to the directory being read and re-runs the cred swap and LSM
probe per child. The encoder amplifies a single answer into one
prepare_kernel_cred() allocation, two LSM hooks, and one put_cred()
RCU callback for every non-directory entry.

No mainstream NFSv4 client has been observed to populate a READDIR
attrmask with these attributes; the Linux client queries them only
via SERVER_CAPS at mount time. The exposure is therefore to test
clients exploring corner cases and to hostile clients that submit
an attrmask designed to multiply server work by rd_dircount.

Probe the directory being read once and cache the result on
struct nfsd4_readdir for use by every non-directory child. The
probe targets the readdir filehandle's dentry, which is held for
the duration of the request, rather than dget_parent() of a
child's locklessly-acquired dentry; the latter could be moved out
of the directory by a concurrent rename and report attributes
from an unrelated parent. Directory entries continue to be
queried individually, because casefold-capable filesystems (ext4,
f2fs) report case state per directory. The other callers of
nfsd4_encode_fattr4() (single GETATTR, the buffer wrapper) pass
NULL for the cache pointer and behave as before.

Reported-by: sashiko-bot <sashiko-bot@kernel.org>
Closes: https://sashiko.dev/#/patchset/20260507-case-sensitivity-v14-0-e62cc8200435@oracle.com?part=14
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Link: https://patch.msgid.link/20260515153515.362266-8-cel@kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>
This commit is contained in:
Chuck Lever 2026-05-15 11:35:15 -04:00 committed by Christian Brauner
parent fbaee2a5c4
commit cfff672ffc
No known key found for this signature in database
GPG Key ID: 91C61BC06578DCA2
2 changed files with 60 additions and 9 deletions
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55
fs/nfsd/nfs4xdr.c
View File

@ -3883,13 +3883,16 @@ static const nfsd4_enc_attr nfsd4_enc_fattr4_encode_ops[] = {
/*
* Note: @fhp can be NULL; in this case, we might have to compose the filehandle
* ourselves.
* ourselves. @case_cache is NULL for callers that encode a single dentry
* (GETATTR, the buffer wrapper); READDIR passes a per-request cache so
* non-directory children share the parent's case-folding probe result.
*/
static __be32
nfsd4_encode_fattr4(struct svc_rqst *rqstp, struct xdr_stream *xdr,
struct svc_fh *fhp, struct svc_export *exp,
struct dentry *dentry, const u32 *bmval,
int ignore_crossmnt)
int ignore_crossmnt,
struct nfsd_case_attrs_cache *case_cache)
{
DECLARE_BITMAP(attr_bitmap, ARRAY_SIZE(nfsd4_enc_fattr4_encode_ops));
struct nfs4_delegation *dp = NULL;
@ -3999,9 +4002,17 @@ nfsd4_encode_fattr4(struct svc_rqst *rqstp, struct xdr_stream *xdr,
args.fhp = fhp;
if (attrmask[0] & (FATTR4_WORD0_CASE_INSENSITIVE |
FATTR4_WORD0_CASE_PRESERVING)) {
err = nfsd_get_case_info(dentry, &args.case_insensitive,
&args.case_preserving);
/*
* In a batched encoder (READDIR) every non-directory
* child shares the same case-folding answer, so the
* directory being read is probed once and the result is
* cached. The probe targets case_cache->dir, the held
* readdir filehandle's dentry, instead of the child's
* locklessly-acquired dentry, which a concurrent rename
* could move under an unrelated parent. Directory
* entries are queried directly because casefold-capable
* filesystems answer per directory.
*
* Per RFC 8881 Section 18.7.3, an attribute advertised
* in SUPPORTED_ATTRS must come back with a value or the
* GETATTR must fail. nfsd_get_case_info() fills POSIX
@ -4011,8 +4022,24 @@ nfsd4_encode_fattr4(struct svc_rqst *rqstp, struct xdr_stream *xdr,
* advertises. Other errors fail the operation as the
* spec requires.
*/
if (err && err != -EOPNOTSUPP)
goto out_nfserr;
if (case_cache && !d_is_dir(dentry)) {
if (!case_cache->valid) {
err = nfsd_get_case_info(case_cache->dir,
&case_cache->insensitive,
&case_cache->preserving);
if (err && err != -EOPNOTSUPP)
goto out_nfserr;
case_cache->valid = true;
}
args.case_insensitive = case_cache->insensitive;
args.case_preserving = case_cache->preserving;
} else {
err = nfsd_get_case_info(dentry,
&args.case_insensitive,
&args.case_preserving);
if (err && err != -EOPNOTSUPP)
goto out_nfserr;
}
}
if (attrmask[0] & FATTR4_WORD0_ACL) {
@ -4170,7 +4197,7 @@ __be32 nfsd4_encode_fattr_to_buf(__be32 **p, int words,
svcxdr_init_encode_from_buffer(&xdr, &dummy, *p, words << 2);
ret = nfsd4_encode_fattr4(rqstp, &xdr, fhp, exp, dentry, bmval,
ignore_crossmnt);
ignore_crossmnt, NULL);
*p = xdr.p;
return ret;
}
@ -4208,6 +4235,7 @@ nfsd4_encode_entry4_fattr(struct nfsd4_readdir *cd, const char *name,
struct dentry *dentry;
__be32 nfserr;
int ignore_crossmnt = 0;
bool crossed = false;
dentry = lookup_one_positive_unlocked(&nop_mnt_idmap,
&QSTR_LEN(name, namlen),
@ -4244,11 +4272,18 @@ nfsd4_encode_entry4_fattr(struct nfsd4_readdir *cd, const char *name,
nfserr = check_nfsd_access(exp, cd->rd_rqstp, false);
if (nfserr)
goto out_put;
crossed = true;
}
out_encode:
/*
* A crossed entry no longer shares a parent with the directory
* being read, so it must neither consume nor populate the
* per-readdir case-folding cache.
*/
nfserr = nfsd4_encode_fattr4(cd->rd_rqstp, cd->xdr, NULL, exp, dentry,
cd->rd_bmval, ignore_crossmnt);
cd->rd_bmval, ignore_crossmnt,
crossed ? NULL : &cd->rd_case_cache);
out_put:
dput(dentry);
exp_put(exp);
@ -4495,7 +4530,7 @@ nfsd4_encode_getattr(struct nfsd4_compoundres *resp, __be32 nfserr,
/* obj_attributes */
return nfsd4_encode_fattr4(resp->rqstp, xdr, fhp, fhp->fh_export,
fhp->fh_dentry, getattr->ga_bmval, 0);
fhp->fh_dentry, getattr->ga_bmval, 0, NULL);
}
static __be32
@ -5022,6 +5057,8 @@ static __be32 nfsd4_encode_dirlist4(struct xdr_stream *xdr,
readdir->rd_maxcount = maxcount;
readdir->common.err = 0;
readdir->cookie_offset = 0;
readdir->rd_case_cache.dir = readdir->rd_fhp->fh_dentry;
readdir->rd_case_cache.valid = false;
offset = readdir->rd_cookie;
status = nfsd_readdir(readdir->rd_rqstp, readdir->rd_fhp, &offset,
&readdir->common, nfsd4_encode_entry4);

14
fs/nfsd/xdr4.h
View File

@ -432,6 +432,19 @@ struct nfsd4_read {
u32 rd_eof; /* response */
};
/*
* Cache the case-folding properties of @dir so a batched encoder
* (e.g., READDIR) does not re-probe per child. @dir is the
* directory being read, held by the request, so it is stable
* against rename for the duration of the cache's lifetime.
*/
struct nfsd_case_attrs_cache {
struct dentry *dir;
bool valid;
bool insensitive;
bool preserving;
};
struct nfsd4_readdir {
u64 rd_cookie; /* request */
nfs4_verifier rd_verf; /* request */
@ -444,6 +457,7 @@ struct nfsd4_readdir {
struct readdir_cd common;
struct xdr_stream *xdr;
int cookie_offset;
struct nfsd_case_attrs_cache rd_case_cache;
};
struct nfsd4_release_lockowner {