FAILED: patch "[PATCH] smb: client: validate dacloffset before building DACL" failed to apply to 5.15-stable tree

PATCH New [email protected] 2 participants 2 messages May 12 – May 16

Subsystems (2)

Stable branch SMB client (CIFS)

lore

Share & tools

lore

[email protected]

author maintainer

2026-05-12 14:04 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 f98b48151cc502ada59d9778f0112d21f2586ca3
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026051249-smartness-undercoat-cf5c@gregkh' --subject-prefix 'PATCH 5.15.y' HEAD^..

Possible dependencies:

thanks,

greg k-h

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

From f98b48151cc502ada59d9778f0112d21f2586ca3 Mon Sep 17 00:00:00 2001
From: Michael Bommarito <[email protected]>
Date: Mon, 20 Apr 2026 10:47:47 -0400
Subject: [PATCH] smb: client: validate dacloffset before building DACL
pointers

parse_sec_desc(), build_sec_desc(), and the chown path in id_mode_to_cifs_acl() all add the server-supplied dacloffset to pntsd before proving a DACL header fits inside the returned security descriptor.

On 32-bit builds a malicious server can return dacloffset near U32_MAX, wrap the derived DACL pointer below end_of_acl, and then slip past the later pointer-based bounds checks. build_sec_desc() and id_mode_to_cifs_acl() can then dereference DACL fields from the wrapped pointer in the chmod/chown rewrite paths.

Validate dacloffset numerically before building any DACL pointer and reuse the same helper at the three DACL entry points.

Fixes bc3e9dd9d104 ("cifs: Change SIDs in ACEs while transferring file ownership.")

Cc [email protected]

Assisted-by Claude:claude-opus-4-6

Signed-off-by Michael Bommarito <[email protected]>

Signed-off-by Steve French <[email protected]>

fs/smb/client/cifsacl.c +32 -3

index a2750f1e3d90..786dbbc43c5b 100644
@@ -1264,6 +1264,17 @@ static int parse_sid(struct smb_sid *psid, char *end_of_acl)
 	return 0;
 }
 
+static bool dacl_offset_valid(unsigned int acl_len, __u32 dacloffset)
+{
+	if (acl_len < sizeof(struct smb_acl))
+		return false;
+
+	if (dacloffset < sizeof(struct smb_ntsd))
+		return false;
+
+	return dacloffset <= acl_len - sizeof(struct smb_acl);
+}
+
 
 /* Convert CIFS ACL to POSIX form */
 static int parse_sec_desc(struct cifs_sb_info *cifs_sb,

@@ -1284,7 +1295,6 @@ static int parse_sec_desc(struct cifs_sb_info *cifs_sb,
 	group_sid_ptr = (struct smb_sid *)((char *)pntsd +
 				le32_to_cpu(pntsd->gsidoffset));
 	dacloffset = le32_to_cpu(pntsd->dacloffset);
-	dacl_ptr = (struct smb_acl *)((char *)pntsd + dacloffset);
 	cifs_dbg(NOISY, "revision %d type 0x%x ooffset 0x%x goffset 0x%x sacloffset 0x%x dacloffset 0x%x\n",
 		 pntsd->revision, pntsd->type, le32_to_cpu(pntsd->osidoffset),
 		 le32_to_cpu(pntsd->gsidoffset),

@@ -1315,11 +1325,18 @@ static int parse_sec_desc(struct cifs_sb_info *cifs_sb,
 		return rc;
 	}
 
-	if (dacloffset)
+	if (dacloffset) {
+		if (!dacl_offset_valid(acl_len, dacloffset)) {
+			cifs_dbg(VFS, "Server returned illegal DACL offset\n");
+			return -EINVAL;
+		}
+
+		dacl_ptr = (struct smb_acl *)((char *)pntsd + dacloffset);
 		parse_dacl(dacl_ptr, end_of_acl, owner_sid_ptr,
 			   group_sid_ptr, fattr, get_mode_from_special_sid);
-	else
+	} else {
 		cifs_dbg(FYI, "no ACL\n"); /* BB grant all or default perms? */
+	}
 
 	return rc;
 }

@@ -1342,6 +1359,11 @@ static int build_sec_desc(struct smb_ntsd *pntsd, struct smb_ntsd *pnntsd,
 
 	dacloffset = le32_to_cpu(pntsd->dacloffset);
 	if (dacloffset) {
+		if (!dacl_offset_valid(secdesclen, dacloffset)) {
+			cifs_dbg(VFS, "Server returned illegal DACL offset\n");
+			return -EINVAL;
+		}
+
 		dacl_ptr = (struct smb_acl *)((char *)pntsd + dacloffset);
 		rc = validate_dacl(dacl_ptr, end_of_acl);
 		if (rc)

@@ -1710,6 +1732,12 @@ id_mode_to_cifs_acl(struct inode *inode, const char *path, __u64 *pnmode,
 		nsecdesclen = sizeof(struct smb_ntsd) + (sizeof(struct smb_sid) * 2);
 		dacloffset = le32_to_cpu(pntsd->dacloffset);
 		if (dacloffset) {
+			if (!dacl_offset_valid(secdesclen, dacloffset)) {
+				cifs_dbg(VFS, "Server returned illegal DACL offset\n");
+				rc = -EINVAL;
+				goto id_mode_to_cifs_acl_exit;
+			}
+
 			dacl_ptr = (struct smb_acl *)((char *)pntsd + dacloffset);
 			rc = validate_dacl(dacl_ptr, (char *)pntsd + secdesclen);
 			if (rc) {

@@ -1752,6 +1780,7 @@ id_mode_to_cifs_acl(struct inode *inode, const char *path, __u64 *pnmode,
 		rc = ops->set_acl(pnntsd, nsecdesclen, inode, path, aclflag);
 		cifs_dbg(NOISY, "set_cifs_acl rc: %d\n", rc);
 	}
+id_mode_to_cifs_acl_exit:
 	cifs_put_tlink(tlink);
 
 	kfree(pnntsd);

Sasha Levin

maintainer

2026-05-16 19:09 UTC #1 lore raw

PATCH 1/1 smb: client: validate dacloffset before building DACL pointers

From: Michael Bommarito <[email protected]>

[ Upstream commit f98b48151cc502ada59d9778f0112d21f2586ca3 ]

Validate dacloffset numerically before building any DACL pointer and reuse the same helper at the three DACL entry points.

Fixes bc3e9dd9d104 ("cifs: Change SIDs in ACEs while transferring file ownership.")

Cc [email protected]

Assisted-by Claude:claude-opus-4-6

Signed-off-by Michael Bommarito <[email protected]>

Signed-off-by Steve French <[email protected]>

[ renamed smb_ntsd/smb_acl structs to cifs_ntsd/cifs_acl and kept existing inline ACL size check instead of using missing validate_dacl() helper ]

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

---
 fs/cifs/cifsacl.c | 35 ++++++++++++++++++++++++++++++++---
 1 file changed, 32 insertions(+), 3 deletions(-)

fs/cifs/cifsacl.c +32 -3

index bf861fef2f0c3..8b8f2d909e1b2 100644
@@ -1183,6 +1183,17 @@ static int parse_sid(struct cifs_sid *psid, char *end_of_acl)
 	return 0;
 }
 
+static bool dacl_offset_valid(unsigned int acl_len, __u32 dacloffset)
+{
+	if (acl_len < sizeof(struct cifs_acl))
+		return false;
+
+	if (dacloffset < sizeof(struct cifs_ntsd))
+		return false;
+
+	return dacloffset <= acl_len - sizeof(struct cifs_acl);
+}
+
 
 /* Convert CIFS ACL to POSIX form */
 static int parse_sec_desc(struct cifs_sb_info *cifs_sb,

@@ -1203,7 +1214,6 @@ static int parse_sec_desc(struct cifs_sb_info *cifs_sb,
 	group_sid_ptr = (struct cifs_sid *)((char *)pntsd +
 				le32_to_cpu(pntsd->gsidoffset));
 	dacloffset = le32_to_cpu(pntsd->dacloffset);
-	dacl_ptr = (struct cifs_acl *)((char *)pntsd + dacloffset);
 	cifs_dbg(NOISY, "revision %d type 0x%x ooffset 0x%x goffset 0x%x sacloffset 0x%x dacloffset 0x%x\n",
 		 pntsd->revision, pntsd->type, le32_to_cpu(pntsd->osidoffset),
 		 le32_to_cpu(pntsd->gsidoffset),

@@ -1234,11 +1244,18 @@ static int parse_sec_desc(struct cifs_sb_info *cifs_sb,
 		return rc;
 	}
 
-	if (dacloffset)
+	if (dacloffset) {
+		if (!dacl_offset_valid(acl_len, dacloffset)) {
+			cifs_dbg(VFS, "Server returned illegal DACL offset\n");
+			return -EINVAL;
+		}
+
+		dacl_ptr = (struct cifs_acl *)((char *)pntsd + dacloffset);
 		parse_dacl(dacl_ptr, end_of_acl, owner_sid_ptr,
 			   group_sid_ptr, fattr, get_mode_from_special_sid);
-	else
+	} else {
 		cifs_dbg(FYI, "no ACL\n"); /* BB grant all or default perms? */
+	}
 
 	return rc;
 }

@@ -1261,6 +1278,11 @@ static int build_sec_desc(struct cifs_ntsd *pntsd, struct cifs_ntsd *pnntsd,
 
 	dacloffset = le32_to_cpu(pntsd->dacloffset);
 	if (dacloffset) {
+		if (!dacl_offset_valid(secdesclen, dacloffset)) {
+			cifs_dbg(VFS, "Server returned illegal DACL offset\n");
+			return -EINVAL;
+		}
+
 		dacl_ptr = (struct cifs_acl *)((char *)pntsd + dacloffset);
 		if (end_of_acl < (char *)dacl_ptr + le16_to_cpu(dacl_ptr->size)) {
 			cifs_dbg(VFS, "Server returned illegal ACL size\n");

@@ -1624,6 +1646,12 @@ id_mode_to_cifs_acl(struct inode *inode, const char *path, __u64 *pnmode,
 		nsecdesclen = sizeof(struct cifs_ntsd) + (sizeof(struct cifs_sid) * 2);
 		dacloffset = le32_to_cpu(pntsd->dacloffset);
 		if (dacloffset) {
+			if (!dacl_offset_valid(secdesclen, dacloffset)) {
+				cifs_dbg(VFS, "Server returned illegal DACL offset\n");
+				rc = -EINVAL;
+				goto id_mode_to_cifs_acl_exit;
+			}
+
 			dacl_ptr = (struct cifs_acl *)((char *)pntsd + dacloffset);
 			if (mode_from_sid)
 				nsecdesclen +=

@@ -1660,6 +1688,7 @@ id_mode_to_cifs_acl(struct inode *inode, const char *path, __u64 *pnmode,
 		rc = ops->set_acl(pnntsd, nsecdesclen, inode, path, aclflag);
 		cifs_dbg(NOISY, "set_cifs_acl rc: %d\n", rc);
 	}
+id_mode_to_cifs_acl_exit:
 	cifs_put_tlink(tlink);
 
 	kfree(pnntsd);

Signature · 1 line

2.53.0