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

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

[Rong Zhang]

After applying this patch, could correctly create symlink:

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

Signed-off-by: Rong Zhang <ulin0208@gmail.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

Re: [PATCH 2/2] ntfs3: correctly create symlink for relative path

[kernel test robot]

Hi Rong,

kernel test robot noticed the following build warnings:

[auto build test WARNING on brauner-vfs/vfs.all]
[also build test WARNING on linus/master v6.15-rc5 next-20250508]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Rong-Zhang/ntfs3-correctly-create-symlink-for-relative-path/20250507-153624
base:   https://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs.git vfs.all
patch link:    https://lore.kernel.org/r/20250507073534.11693-1-ulin0208%40gmail.com
patch subject: [PATCH 2/2] ntfs3: correctly create symlink for relative path
config: i386-randconfig-r133-20250508 (https://download.01.org/0day-ci/archive/20250509/202505090114.Ejj1rsY0-lkp@intel.com/config)
compiler: gcc-12 (Debian 12.2.0-14) 12.2.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20250509/202505090114.Ejj1rsY0-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202505090114.Ejj1rsY0-lkp@intel.com/

sparse warnings: (new ones prefixed by >>)
>> fs/ntfs3/inode.c:1124:19: sparse: sparse: incorrect type in assignment (different base types) @@     expected restricted __le32 [usertype] Flags @@     got int @@
   fs/ntfs3/inode.c:1124:19: sparse:     expected restricted __le32 [usertype] Flags
   fs/ntfs3/inode.c:1124:19: sparse:     got int

vim +1124 fs/ntfs3/inode.c

  1068	
  1069	static struct REPARSE_DATA_BUFFER *
  1070	ntfs_create_reparse_buffer(struct ntfs_sb_info *sbi, const char *symname,
  1071				   u32 size, u16 *nsize)
  1072	{
  1073		int i, err;
  1074		struct REPARSE_DATA_BUFFER *rp;
  1075		__le16 *rp_name;
  1076		typeof(rp->SymbolicLinkReparseBuffer) *rs;
  1077		bool is_absolute;
  1078	
  1079		is_absolute = (strlen(symname) > 1 && symname[1] == ':');
  1080	
  1081		rp = kzalloc(ntfs_reparse_bytes(2 * size + 2, is_absolute), GFP_NOFS);
  1082		if (!rp)
  1083			return ERR_PTR(-ENOMEM);
  1084	
  1085		rs = &rp->SymbolicLinkReparseBuffer;
  1086		rp_name = rs->PathBuffer;
  1087	
  1088		/* Convert link name to UTF-16. */
  1089		err = ntfs_nls_to_utf16(sbi, symname, size,
  1090					(struct cpu_str *)(rp_name - 1), 2 * size,
  1091					UTF16_LITTLE_ENDIAN);
  1092		if (err < 0)
  1093			goto out;
  1094	
  1095		/* err = the length of unicode name of symlink. */
  1096		*nsize = ntfs_reparse_bytes(err, is_absolute);
  1097	
  1098		if (*nsize > sbi->reparse.max_size) {
  1099			err = -EFBIG;
  1100			goto out;
  1101		}
  1102	
  1103		/* Translate Linux '/' into Windows '\'. */
  1104		for (i = 0; i < err; i++) {
  1105			if (rp_name[i] == cpu_to_le16('/'))
  1106				rp_name[i] = cpu_to_le16('\\');
  1107		}
  1108	
  1109		rp->ReparseTag = IO_REPARSE_TAG_SYMLINK;
  1110		rp->ReparseDataLength =
  1111			cpu_to_le16(*nsize - offsetof(struct REPARSE_DATA_BUFFER,
  1112						      SymbolicLinkReparseBuffer));
  1113	
  1114		/* PrintName + SubstituteName. */
  1115		rs->SubstituteNameOffset = cpu_to_le16(sizeof(short) * err);
  1116		rs->SubstituteNameLength = cpu_to_le16(sizeof(short) * err + (is_absolute ? 8 : 0));
  1117		rs->PrintNameLength = rs->SubstituteNameOffset;
  1118	
  1119		/*
  1120		 * TODO: Use relative path if possible to allow Windows to
  1121		 * parse this path.
  1122		 * 0-absolute path 1- relative path (SYMLINK_FLAG_RELATIVE).
  1123		 */
> 1124		rs->Flags = is_absolute ? 0 : SYMLINK_FLAG_RELATIVE;
  1125	
  1126		memmove(rp_name + err + (is_absolute ? 4 : 0), rp_name, sizeof(short) * err);
  1127	
  1128		if (is_absolute) {
  1129			/* Decorate SubstituteName. */
  1130			rp_name += err;
  1131			rp_name[0] = cpu_to_le16('\\');
  1132			rp_name[1] = cpu_to_le16('?');
  1133			rp_name[2] = cpu_to_le16('?');
  1134			rp_name[3] = cpu_to_le16('\\');
  1135		}
  1136	
  1137		return rp;
  1138	out:
  1139		kfree(rp);
  1140		return ERR_PTR(err);
  1141	}
  1142	

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki