FAILED: patch "[PATCH] NFSD: check truncate permission under inode lock" failed to apply to 5.15-stable tree

PATCH New [email protected] 2 participants 3 messages Sep 3 – Sep 5

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lore

[email protected]

author maintainer

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

The patch below does not apply to the 5.15-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-5.15.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 '2026090340-copier-another-5c3a@gregkh' --subject-prefix 'PATCH 5.15.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

2026-09-05 00:15 UTC #1 lore raw

PATCH 1/2 nfsd: don't provide pre/post-op attrs if fh_getattr fails

From: Jeff Layton <[email protected]>

[ Upstream commit 518f375c15af724cd89a4ec888dea942bb27f77f ]

nfsd calls fh_getattr to get the latest inode attrs for pre/post-op info. In the event that fh_getattr fails, it resorts to scraping cached values out of the inode directly.

Since these attributes are optional, we can just skip providing them altogether when this happens.

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

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

Reviewed-by Neil Brown <[email protected]>

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

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

---
 fs/nfsd/auth.c      | 15 +++++++--------
 fs/nfsd/auth.h      |  2 +-
 fs/nfsd/export.h    |  3 ++-
 fs/nfsd/nfs4state.c |  3 ++-
 fs/nfsd/nfsfh.c     | 29 +++++++++++++----------------
 fs/nfsd/nfsfh.h     |  2 +-
 fs/nfsd/nfsproc.c   |  9 +++++----
 fs/nfsd/vfs.c       | 27 +++++++++++++++++----------
 fs/nfsd/vfs.h       |  4 ++--
 9 files changed, 50 insertions(+), 44 deletions(-)

fs/nfsd/auth.c +7 -8

index fdf2aad734709..bcf207bc24f96 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);
 
 	validate_process_creds();

@@ -34,10 +34,10 @@ 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;

@@ -91,4 +91,3 @@ int nfsd_setuser(struct svc_rqst *rqstp, struct svc_export *exp)
 	abort_creds(new);
 	return -ENOMEM;
 }
-

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 f73e23bb24a1e..4965e294d1e1c 100644
@@ -98,7 +98,8 @@ 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_nfsd_access(struct svc_export *exp, struct svc_rqst *rqstp);
 
 /*

fs/nfsd/nfs4state.c +2 -1

index e6c0b1520973e..18c014961e084 100644
@@ -6561,7 +6561,8 @@ 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 +13 ~~-16~~

index e73e9d44f1b0c..d6d5bb0a19a25 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,

@@ -392,7 +392,7 @@ 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)

@@ -612,7 +612,7 @@ fh_update(struct svc_fh *fhp)
  * @fhp: file handle to be updated
  *
  */
-void fh_fill_pre_attrs(struct svc_fh *fhp)
+__be32 fh_fill_pre_attrs(struct svc_fh *fhp)
 {
 	bool v4 = (fhp->fh_maxsize == NFS4_FHSIZE);
 	struct inode *inode;

@@ -620,16 +620,13 @@ void fh_fill_pre_attrs(struct svc_fh *fhp)
 	__be32 err;
 
 	if (fhp->fh_no_wcc || fhp->fh_pre_saved)
-		return;
+		return nfs_ok;
 
 	inode = d_inode(fhp->fh_dentry);
 	err = fh_getattr(fhp, &stat);
-	if (err) {
-		/* Grab the times from inode anyway */
-		stat.mtime = inode->i_mtime;
-		stat.ctime = inode->i_ctime;
-		stat.size  = inode->i_size;
-	}
+	if (err)
+		return err;
+
 	if (v4)
 		fhp->fh_pre_change = nfsd4_change_attribute(&stat, inode);

@@ -637,6 +634,7 @@ void fh_fill_pre_attrs(struct svc_fh *fhp)
 	fhp->fh_pre_ctime = stat.ctime;
 	fhp->fh_pre_size  = stat.size;
 	fhp->fh_pre_saved = true;
+	return nfs_ok;
 }
 
 /**

@@ -657,11 +655,10 @@ void fh_fill_post_attrs(struct svc_fh *fhp)
 		printk("nfsd: inode locked twice during operation.\n");
 
 	err = fh_getattr(fhp, &fhp->fh_post_attr);
-	if (err) {
-		fhp->fh_post_saved = false;
-		fhp->fh_post_attr.ctime = inode->i_ctime;
-	} else
-		fhp->fh_post_saved = true;
+	if (err)
+		return;
+
+	fhp->fh_post_saved = true;
 	if (v4)
 		fhp->fh_post_change =
 			nfsd4_change_attribute(&fhp->fh_post_attr, inode);

fs/nfsd/nfsfh.h +1 -1

index 40aee06ebd952..242e34bd9b631 100644
@@ -314,7 +314,7 @@ static inline u64 nfsd4_change_attribute(struct kstat *stat,
 		return time_to_chattr(&stat->ctime);
 }
 
-extern void fh_fill_pre_attrs(struct svc_fh *fhp);
+extern __be32 fh_fill_pre_attrs(struct svc_fh *fhp);
 extern void fh_fill_post_attrs(struct svc_fh *fhp);
 extern void fh_fill_both_attrs(struct svc_fh *fhp);
 #endif /* _LINUX_NFSD_NFSFH_H */

fs/nfsd/nfsproc.c +5 -4

index 9744443c39652..59b6a2e41a079 100644
@@ -343,10 +343,11 @@ 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 +17 ~~-10~~

index 7b0bc4507ad04..25dc416d82342 100644
@@ -400,8 +400,9 @@ 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;
 	}

@@ -533,7 +534,10 @@ nfsd_setattr(struct svc_rqst *rqstp, struct svc_fh *fhp,
 	}
 
 	inode_lock(inode);
-	fh_fill_pre_attrs(fhp);
+	err = fh_fill_pre_attrs(fhp);
+	if (err)
+		goto out_unlock;
+
 	for (retries = 1;;) {
 		struct iattr attrs;

@@ -562,6 +566,7 @@ nfsd_setattr(struct svc_rqst *rqstp, struct svc_fh *fhp,
 						inode, ACL_TYPE_DEFAULT,
 						attr->na_dpacl);
 	fh_fill_post_attrs(fhp);
+out_unlock:
 	inode_unlock(inode);
 	if (size_change)
 		put_write_access(inode);

@@ -778,7 +783,8 @@ 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;

@@ -1379,7 +1385,8 @@ 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;

@@ -2093,9 +2100,9 @@ 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

@@ -2338,8 +2345,8 @@ 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;

@@ -2370,7 +2377,7 @@ 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 dbdfef7ae85bb..219b479dabc70 100644
@@ -145,8 +145,8 @@ __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

2026-09-05 00:15 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 25dc416d82342..b26eaa23f435b 100644
@@ -392,21 +392,22 @@ 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)

@@ -528,12 +529,17 @@ 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