linux-kernel - [PATCH 2/2] ntfs3: correctly create symlink for relative path

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Message-ID: <20250507073534.11693-1-ulin0208@gmail.com>
Date: Wed,  7 May 2025 15:35:34 +0800
From: Rong Zhang <ulin0208@...il.com>
To: almaz.alexandrovich@...agon-software.com
Cc: ntfs3@...ts.linux.dev,
	linux-kernel@...r.kernel.org,
	Rong Zhang <ulin0208@...il.com>
Subject: [PATCH 2/2] ntfs3: correctly create symlink for relative path

After applying this patch, could correctly create symlink:

ln -s "relative/path/to/file" symlink

Signed-off-by: Rong Zhang <ulin0208@...il.com>
---
 fs/ntfs3/inode.c | 31 ++++++++++++++++++-------------
 1 file changed, 18 insertions(+), 13 deletions(-)

diff --git a/fs/ntfs3/inode.c b/fs/ntfs3/inode.c
index 2641738d2934..7c79c2c7eff6 100644
--- a/fs/ntfs3/inode.c
+++ b/fs/ntfs3/inode.c
@@ -1098,10 +1098,10 @@ int inode_read_data(struct inode *inode, void *data, size_t bytes)
  * Number of bytes for REPARSE_DATA_BUFFER(IO_REPARSE_TAG_SYMLINK)
  * for unicode string of @uni_len length.
  */
-static inline u32 ntfs_reparse_bytes(u32 uni_len)
+static inline u32 ntfs_reparse_bytes(u32 uni_len, bool is_absolute)
 {
 	/* Header + unicode string + decorated unicode string. */
-	return sizeof(short) * (2 * uni_len + 4) +
+	return sizeof(short) * (2 * uni_len + (is_absolute ? 4 : 0)) +
 	       offsetof(struct REPARSE_DATA_BUFFER,
 			SymbolicLinkReparseBuffer.PathBuffer);
 }
@@ -1114,8 +1114,11 @@ ntfs_create_reparse_buffer(struct ntfs_sb_info *sbi, const char *symname,
 	struct REPARSE_DATA_BUFFER *rp;
 	__le16 *rp_name;
 	typeof(rp->SymbolicLinkReparseBuffer) *rs;
+	bool is_absolute;
 
-	rp = kzalloc(ntfs_reparse_bytes(2 * size + 2), GFP_NOFS);
+	is_absolute = (strlen(symname) > 1 && symname[1] == ':');
+
+	rp = kzalloc(ntfs_reparse_bytes(2 * size + 2, is_absolute), GFP_NOFS);
 	if (!rp)
 		return ERR_PTR(-ENOMEM);
 
@@ -1130,7 +1133,7 @@ ntfs_create_reparse_buffer(struct ntfs_sb_info *sbi, const char *symname,
 		goto out;
 
 	/* err = the length of unicode name of symlink. */
-	*nsize = ntfs_reparse_bytes(err);
+	*nsize = ntfs_reparse_bytes(err, is_absolute);
 
 	if (*nsize > sbi->reparse.max_size) {
 		err = -EFBIG;
@@ -1150,7 +1153,7 @@ ntfs_create_reparse_buffer(struct ntfs_sb_info *sbi, const char *symname,
 
 	/* PrintName + SubstituteName. */
 	rs->SubstituteNameOffset = cpu_to_le16(sizeof(short) * err);
-	rs->SubstituteNameLength = cpu_to_le16(sizeof(short) * err + 8);
+	rs->SubstituteNameLength = cpu_to_le16(sizeof(short) * err + (is_absolute ? 8 : 0));
 	rs->PrintNameLength = rs->SubstituteNameOffset;
 
 	/*
@@ -1158,16 +1161,18 @@ ntfs_create_reparse_buffer(struct ntfs_sb_info *sbi, const char *symname,
 	 * parse this path.
 	 * 0-absolute path 1- relative path (SYMLINK_FLAG_RELATIVE).
 	 */
-	rs->Flags = 0;
+	rs->Flags = is_absolute ? 0 : SYMLINK_FLAG_RELATIVE;
 
-	memmove(rp_name + err + 4, rp_name, sizeof(short) * err);
+	memmove(rp_name + err + (is_absolute ? 4 : 0), rp_name, sizeof(short) * err);
 
-	/* Decorate SubstituteName. */
-	rp_name += err;
-	rp_name[0] = cpu_to_le16('\\');
-	rp_name[1] = cpu_to_le16('?');
-	rp_name[2] = cpu_to_le16('?');
-	rp_name[3] = cpu_to_le16('\\');
+	if (is_absolute) {
+		/* Decorate SubstituteName. */
+		rp_name += err;
+		rp_name[0] = cpu_to_le16('\\');
+		rp_name[1] = cpu_to_le16('?');
+		rp_name[2] = cpu_to_le16('?');
+		rp_name[3] = cpu_to_le16('\\');
+	}
 
 	return rp;
 out:
-- 
2.49.0