FAILED: patch "[PATCH] NFSD: check truncate permission under inode lock" failed to apply to 6.6-stable tree

PATCH New [email protected] 2 participants 3 messages Sep 3 – Sep 4

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[email protected]

author maintainer

2026-09-03 13:07 UTC #0 lore raw

The patch below does not apply to the 6.6-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.6.y
git checkout FETCH_HEAD
git cherry-pick -x b778e0e0a16759f22a70579c3cf8d254a40d4a7f
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026090339-resolute-antennae-cd2d@gregkh' --subject-prefix 'PATCH 6.6.y' 'HEAD^..'

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From b778e0e0a16759f22a70579c3cf8d254a40d4a7f Mon Sep 17 00:00:00 2001
From: Chuck Lever <[email protected]>
Date: Sat, 30 May 2026 09:19:22 -0400
Subject: [PATCH] NFSD: check truncate permission under inode lock

nfsd_setattr() checks whether a size update needs NFSD_MAY_TRUNC before it takes inode_lock(). The comparison uses the file size sampled by that unlocked read, but the actual ATTR_SIZE update is applied later under inode_lock() by notify_change().

This leaves a TOCTOU window for append-only files. If a client sends a SETATTR that does not shrink the file at the time of the unlocked sample, a concurrent append can extend the file before nfsd_setattr() takes inode_lock(). notify_change() then applies a real truncation without the NFSD_MAY_TRUNC check that rejects IS_APPEND(inode). The VFS truncate syscall paths perform their own append-only checks before calling notify_change(), so NFSD must make this decision against the locked size it is about to change.

Split the write-count acquisition from the truncation permission check. Keep get_write_access() before the locked setattr work, then recheck whether the requested size is below i_size_read(inode) after inode_lock() has been acquired and before notify_change(ATTR_SIZE). This also avoids the plain unlocked inode->i_size load.

Fixes 783112f7401f ("nfsd: special case truncates some more")

Cc [email protected]

Assisted-by kres:claude-opus-4-7

Reported-by Chris Mason <[email protected]>

Signed-off-by Jeff Layton <[email protected]>

Link https://patch.msgid.link/[email protected] open here

Signed-off-by Chuck Lever <[email protected]>

fs/nfsd/vfs.c +18 ~~-12~~

index 1e89c7ff9493..a3940548136f 100644
@@ -419,21 +419,22 @@ nfsd_sanitize_attrs(struct inode *inode, struct iattr *iap)
 }
 
 static __be32
-nfsd_get_write_access(struct svc_rqst *rqstp, struct svc_fh *fhp,
-		struct iattr *iap)
+nfsd_may_truncate(struct svc_rqst *rqstp, struct svc_fh *fhp,
+		  struct iattr *iap)
 {
 	struct inode *inode = d_inode(fhp->fh_dentry);
 
-	if (iap->ia_size < inode->i_size) {
-		__be32 err;
+	if (iap->ia_size >= i_size_read(inode))
+		return nfs_ok;
 
-		err = nfsd_permission(&rqstp->rq_cred,
-				      fhp->fh_export, fhp->fh_dentry,
-				      NFSD_MAY_TRUNC | NFSD_MAY_OWNER_OVERRIDE);
-		if (err)
-			return err;
-	}
-	return nfserrno(get_write_access(inode));
+	return nfsd_permission(&rqstp->rq_cred, fhp->fh_export, fhp->fh_dentry,
+			       NFSD_MAY_TRUNC | NFSD_MAY_OWNER_OVERRIDE);
+}
+
+static __be32
+nfsd_get_write_access(struct svc_fh *fhp)
+{
+	return nfserrno(get_write_access(d_inode(fhp->fh_dentry)));
 }
 
 static int __nfsd_setattr(struct dentry *dentry, struct iattr *iap)

@@ -560,12 +561,17 @@ nfsd_setattr(struct svc_rqst *rqstp, struct svc_fh *fhp,
 	 * setattr call.
 	 */
 	if (size_change) {
-		err = nfsd_get_write_access(rqstp, fhp, iap);
+		err = nfsd_get_write_access(fhp);
 		if (err)
 			return err;
 	}
 
 	inode_lock(inode);
+	if (size_change) {
+		err = nfsd_may_truncate(rqstp, fhp, iap);
+		if (err)
+			goto out_unlock;
+	}
 	err = fh_fill_pre_attrs(fhp);
 	if (err)
 		goto out_unlock;

Sasha Levin

maintainer

2026-09-04 20:31 UTC #1 lore raw

PATCH 1/2 nfsd: Pass 'cred' instead of 'rqstp' to some functions.

From: NeilBrown <[email protected]>

[ Upstream commit 9fd45c16f3e3b95b458e049c77f4d7dfef673a52 ]

nfsd_permission(), exp_rdonly(), nfsd_setuser(), and nfsexp_flags() only ever need the cred out of rqstp, so pass it explicitly instead of the whole rqstp.

This makes the interfaces cleaner.

Signed-off-by NeilBrown <[email protected]>

Reviewed-by Jeff Layton <[email protected]>

Signed-off-by Chuck Lever <[email protected]>

Stable-dep-of: b778e0e0a167 ("NFSD: check truncate permission under inode lock")

Signed-off-by Sasha Levin <[email protected]>

---
 fs/nfsd/auth.c      | 14 +++++++-------
 fs/nfsd/auth.h      |  2 +-
 fs/nfsd/export.h    |  3 ++-
 fs/nfsd/nfs4state.c |  3 ++-
 fs/nfsd/nfsfh.c     |  6 +++---
 fs/nfsd/nfsproc.c   |  9 +++++----
 fs/nfsd/vfs.c       | 21 ++++++++++++---------
 fs/nfsd/vfs.h       |  4 ++--
 8 files changed, 34 insertions(+), 28 deletions(-)

fs/nfsd/auth.c +7 -7

index e6beaaf4f1700..93e33d1ee8917 100644
@@ -5,26 +5,26 @@
 #include "nfsd.h"
 #include "auth.h"
 
-int nfsexp_flags(struct svc_rqst *rqstp, struct svc_export *exp)
+int nfsexp_flags(struct svc_cred *cred, struct svc_export *exp)
 {
 	struct exp_flavor_info *f;
 	struct exp_flavor_info *end = exp->ex_flavors + exp->ex_nflavors;
 
 	for (f = exp->ex_flavors; f < end; f++) {
-		if (f->pseudoflavor == rqstp->rq_cred.cr_flavor)
+		if (f->pseudoflavor == cred->cr_flavor)
 			return f->flags;
 	}
 	return exp->ex_flags;
 
 }
 
-int nfsd_setuser(struct svc_rqst *rqstp, struct svc_export *exp)
+int nfsd_setuser(struct svc_cred *cred, struct svc_export *exp)
 {
 	struct group_info *rqgi;
 	struct group_info *gi;
 	struct cred *new;
 	int i;
-	int flags = nfsexp_flags(rqstp, exp);
+	int flags = nfsexp_flags(cred, exp);
 
 	/* discard any old override before preparing the new set */
 	revert_creds(get_cred(current_real_cred()));

@@ -32,10 +32,10 @@ int nfsd_setuser(struct svc_rqst *rqstp, struct svc_export *exp)
 	if (!new)
 		return -ENOMEM;
 
-	new->fsuid = rqstp->rq_cred.cr_uid;
-	new->fsgid = rqstp->rq_cred.cr_gid;
+	new->fsuid = cred->cr_uid;
+	new->fsgid = cred->cr_gid;
 
-	rqgi = rqstp->rq_cred.cr_group_info;
+	rqgi = cred->cr_group_info;
 
 	if (flags & NFSEXP_ALLSQUASH) {
 		new->fsuid = exp->ex_anon_uid;

fs/nfsd/auth.h +1 -1

index dbd66424f600b..8c5031bbbcee2 100644
@@ -12,6 +12,6 @@
  * Set the current process's fsuid/fsgid etc to those of the NFS
  * client user
  */
-int nfsd_setuser(struct svc_rqst *, struct svc_export *);
+int nfsd_setuser(struct svc_cred *cred, struct svc_export *exp);
 
 #endif /* LINUX_NFSD_AUTH_H */

fs/nfsd/export.h +2 -1

index 4a48b2ad56067..3174fc05bf02a 100644
@@ -99,7 +99,8 @@ struct svc_expkey {
 #define EX_NOHIDE(exp)		((exp)->ex_flags & NFSEXP_NOHIDE)
 #define EX_WGATHER(exp)		((exp)->ex_flags & NFSEXP_GATHERED_WRITES)
 
-int nfsexp_flags(struct svc_rqst *rqstp, struct svc_export *exp);
+struct svc_cred;
+int nfsexp_flags(struct svc_cred *cred, struct svc_export *exp);
 __be32 check_xprtsec_policy(struct svc_export *exp, struct svc_rqst *rqstp);
 __be32 check_security_flavor(struct svc_export *exp, struct svc_rqst *rqstp);
 __be32 check_nfsd_access(struct svc_export *exp, struct svc_rqst *rqstp);

fs/nfsd/nfs4state.c +2 -1

index f21878a7f3939..586f2677c294c 100644
@@ -6605,7 +6605,8 @@ nfs4_check_file(struct svc_rqst *rqstp, struct svc_fh *fhp, struct nfs4_stid *s,
 
 	nf = nfs4_find_file(s, flags);
 	if (nf) {
-		status = nfsd_permission(rqstp, fhp->fh_export, fhp->fh_dentry,
+		status = nfsd_permission(&rqstp->rq_cred,
+					 fhp->fh_export, fhp->fh_dentry,
 				acc | NFSD_MAY_OWNER_OVERRIDE);
 		if (status) {
 			nfsd_file_put(nf);

fs/nfsd/nfsfh.c +3 -3

index 283c1a60c8460..e41c1efc46997 100644
@@ -102,7 +102,7 @@ static bool nfsd_originating_port_ok(struct svc_rqst *rqstp, int flags)
 static __be32 nfsd_setuser_and_check_port(struct svc_rqst *rqstp,
 					  struct svc_export *exp)
 {
-	int flags = nfsexp_flags(rqstp, exp);
+	int flags = nfsexp_flags(&rqstp->rq_cred, exp);
 
 	/* Check if the request originated from a secure port. */
 	if (!nfsd_originating_port_ok(rqstp, flags)) {

@@ -113,7 +113,7 @@ static __be32 nfsd_setuser_and_check_port(struct svc_rqst *rqstp,
 	}
 
 	/* Set user creds for this exportpoint */
-	return nfserrno(nfsd_setuser(rqstp, exp));
+	return nfserrno(nfsd_setuser(&rqstp->rq_cred, exp));
 }
 
 static inline __be32 check_pseudo_root(struct svc_rqst *rqstp,

@@ -402,7 +402,7 @@ fh_verify(struct svc_rqst *rqstp, struct svc_fh *fhp, umode_t type, int access)
 
 skip_pseudoflavor_check:
 	/* Finally, check access permissions. */
-	error = nfsd_permission(rqstp, exp, dentry, access);
+	error = nfsd_permission(&rqstp->rq_cred, exp, dentry, access);
 out:
 	trace_nfsd_fh_verify_err(rqstp, fhp, type, access, error);
 	if (error == nfserr_stale)

fs/nfsd/nfsproc.c +5 -4

index 36370b957b633..97aab34593ef0 100644
@@ -331,10 +331,11 @@ nfsd_proc_create(struct svc_rqst *rqstp)
 					 *   echo thing > device-special-file-or-pipe
 					 * by doing a CREATE with type==0
 					 */
-					resp->status = nfsd_permission(rqstp,
-								 newfhp->fh_export,
-								 newfhp->fh_dentry,
-								 NFSD_MAY_WRITE|NFSD_MAY_LOCAL_ACCESS);
+					resp->status = nfsd_permission(
+						&rqstp->rq_cred,
+						newfhp->fh_export,
+						newfhp->fh_dentry,
+						NFSD_MAY_WRITE|NFSD_MAY_LOCAL_ACCESS);
 					if (resp->status && resp->status != nfserr_rofs)
 						goto out_unlock;
 				}

fs/nfsd/vfs.c +12 -9

index 5dc798e89e97b..200fe34a104c7 100644
@@ -423,8 +423,9 @@ nfsd_get_write_access(struct svc_rqst *rqstp, struct svc_fh *fhp,
 	if (iap->ia_size < inode->i_size) {
 		__be32 err;
 
-		err = nfsd_permission(rqstp, fhp->fh_export, fhp->fh_dentry,
-				NFSD_MAY_TRUNC | NFSD_MAY_OWNER_OVERRIDE);
+		err = nfsd_permission(&rqstp->rq_cred,
+				      fhp->fh_export, fhp->fh_dentry,
+				      NFSD_MAY_TRUNC | NFSD_MAY_OWNER_OVERRIDE);
 		if (err)
 			return err;
 	}

@@ -809,7 +810,8 @@ nfsd_access(struct svc_rqst *rqstp, struct svc_fh *fhp, u32 *access, u32 *suppor
 
 			sresult |= map->access;
 
-			err2 = nfsd_permission(rqstp, export, dentry, map->how);
+			err2 = nfsd_permission(&rqstp->rq_cred, export,
+					       dentry, map->how);
 			switch (err2) {
 			case nfs_ok:
 				result |= map->access;

@@ -1453,7 +1455,8 @@ nfsd_create_locked(struct svc_rqst *rqstp, struct svc_fh *fhp,
 	dirp = d_inode(dentry);
 
 	dchild = dget(resfhp->fh_dentry);
-	err = nfsd_permission(rqstp, fhp->fh_export, dentry, NFSD_MAY_CREATE);
+	err = nfsd_permission(&rqstp->rq_cred, fhp->fh_export, dentry,
+			      NFSD_MAY_CREATE);
 	if (err)
 		goto out;

@@ -2180,9 +2183,9 @@ nfsd_statfs(struct svc_rqst *rqstp, struct svc_fh *fhp, struct kstatfs *stat, in
 	return err;
 }
 
-static int exp_rdonly(struct svc_rqst *rqstp, struct svc_export *exp)
+static int exp_rdonly(struct svc_cred *cred, struct svc_export *exp)
 {
-	return nfsexp_flags(rqstp, exp) & NFSEXP_READONLY;
+	return nfsexp_flags(cred, exp) & NFSEXP_READONLY;
 }
 
 #ifdef CONFIG_NFSD_V4

@@ -2426,8 +2429,8 @@ nfsd_setxattr(struct svc_rqst *rqstp, struct svc_fh *fhp, char *name,
  * Check for a user's access permissions to this inode.
  */
 __be32
-nfsd_permission(struct svc_rqst *rqstp, struct svc_export *exp,
-					struct dentry *dentry, int acc)
+nfsd_permission(struct svc_cred *cred, struct svc_export *exp,
+		struct dentry *dentry, int acc)
 {
 	struct inode	*inode = d_inode(dentry);
 	int		err;

@@ -2458,7 +2461,7 @@ nfsd_permission(struct svc_rqst *rqstp, struct svc_export *exp,
 	 */
 	if (!(acc & NFSD_MAY_LOCAL_ACCESS))
 		if (acc & (NFSD_MAY_WRITE | NFSD_MAY_SATTR | NFSD_MAY_TRUNC)) {
-			if (exp_rdonly(rqstp, exp) ||
+			if (exp_rdonly(cred, exp) ||
 			    __mnt_is_readonly(exp->ex_path.mnt))
 				return nfserr_rofs;
 			if (/* (acc & NFSD_MAY_WRITE) && */ IS_IMMUTABLE(inode))

fs/nfsd/vfs.h +2 -2

index bf695d5cc04e4..6c41770efe33d 100644
@@ -153,8 +153,8 @@ __be32		nfsd_readdir(struct svc_rqst *, struct svc_fh *,
 __be32		nfsd_statfs(struct svc_rqst *, struct svc_fh *,
 				struct kstatfs *, int access);
 
-__be32		nfsd_permission(struct svc_rqst *, struct svc_export *,
-				struct dentry *, int);
+__be32		nfsd_permission(struct svc_cred *cred, struct svc_export *exp,
+				struct dentry *dentry, int acc);
 
 static inline int fh_want_write(struct svc_fh *fh)
 {

Signature · 1 line

2.53.0

Sasha Levin

maintainer

2026-09-04 20:31 UTC #2 lore raw

PATCH 2/2 NFSD: check truncate permission under inode lock

From: Chuck Lever <[email protected]>

[ Upstream commit b778e0e0a16759f22a70579c3cf8d254a40d4a7f ]

Fixes 783112f7401f ("nfsd: special case truncates some more")

Cc [email protected]

Assisted-by kres:claude-opus-4-7

Reported-by Chris Mason <[email protected]>

Signed-off-by Jeff Layton <[email protected]>

Link https://patch.msgid.link/[email protected] open here

Signed-off-by Chuck Lever <[email protected]>

Signed-off-by Sasha Levin <[email protected]>

---
 fs/nfsd/vfs.c | 30 ++++++++++++++++++------------
 1 file changed, 18 insertions(+), 12 deletions(-)

fs/nfsd/vfs.c +18 ~~-12~~

index 200fe34a104c7..0d81ffc254bad 100644
@@ -415,21 +415,22 @@ nfsd_sanitize_attrs(struct inode *inode, struct iattr *iap)
 }
 
 static __be32
-nfsd_get_write_access(struct svc_rqst *rqstp, struct svc_fh *fhp,
-		struct iattr *iap)
+nfsd_may_truncate(struct svc_rqst *rqstp, struct svc_fh *fhp,
+		  struct iattr *iap)
 {
 	struct inode *inode = d_inode(fhp->fh_dentry);
 
-	if (iap->ia_size < inode->i_size) {
-		__be32 err;
+	if (iap->ia_size >= i_size_read(inode))
+		return nfs_ok;
 
-		err = nfsd_permission(&rqstp->rq_cred,
-				      fhp->fh_export, fhp->fh_dentry,
-				      NFSD_MAY_TRUNC | NFSD_MAY_OWNER_OVERRIDE);
-		if (err)
-			return err;
-	}
-	return nfserrno(get_write_access(inode));
+	return nfsd_permission(&rqstp->rq_cred, fhp->fh_export, fhp->fh_dentry,
+			       NFSD_MAY_TRUNC | NFSD_MAY_OWNER_OVERRIDE);
+}
+
+static __be32
+nfsd_get_write_access(struct svc_fh *fhp)
+{
+	return nfserrno(get_write_access(d_inode(fhp->fh_dentry)));
 }
 
 static int __nfsd_setattr(struct dentry *dentry, struct iattr *iap)

@@ -546,12 +547,17 @@ nfsd_setattr(struct svc_rqst *rqstp, struct svc_fh *fhp,
 	 * setattr call.
 	 */
 	if (size_change) {
-		err = nfsd_get_write_access(rqstp, fhp, iap);
+		err = nfsd_get_write_access(fhp);
 		if (err)
 			return err;
 	}
 
 	inode_lock(inode);
+	if (size_change) {
+		err = nfsd_may_truncate(rqstp, fhp, iap);
+		if (err)
+			goto out_unlock;
+	}
 	err = fh_fill_pre_attrs(fhp);
 	if (err)
 		goto out_unlock;

Signature · 1 line

2.53.0