From: Chuck Lever Date: Fri, 15 May 2026 15:35:15 +0000 (-0400) Subject: nfsd: Cap case-folding probe cost across READDIR entries X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=cfff672ffcf9a74b560c2002739729f91812e398;p=thirdparty%2Flinux.git nfsd: Cap case-folding probe cost across READDIR entries 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 Closes: https://sashiko.dev/#/patchset/20260507-case-sensitivity-v14-0-e62cc8200435@oracle.com?part=14 Signed-off-by: Chuck Lever Link: https://patch.msgid.link/20260515153515.362266-8-cel@kernel.org Signed-off-by: Christian Brauner --- diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c index 319007b79d49f..20355dc3f1d16 100644 --- a/fs/nfsd/nfs4xdr.c +++ b/fs/nfsd/nfs4xdr.c @@ -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); diff --git a/fs/nfsd/xdr4.h b/fs/nfsd/xdr4.h index 417e9ad9fbb39..615797df218fd 100644 --- a/fs/nfsd/xdr4.h +++ b/fs/nfsd/xdr4.h @@ -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 {