[PATCH v2] smb: client: preserve leading slash for POSIX absolute symlink targets

[PATCH v2] smb: client: preserve leading slash for POSIX absolute symlink targets

[Steve French]

When creating a native SMB symbolic link (CIFS_SYMLINK_TYPE_NATIVE) whose
target is an absolute path on a mount that uses POSIX paths, the leading
path separator was silently dropped from the stored symlink target.

create_native_symlink() converted the target to UTF-16 with
cifs_convert_path_to_utf16().  That helper is intended for share-relative
SMB paths and therefore unconditionally strips a leading path separator.
For an absolute POSIX symlink target the leading '/' is significant, so a
target of "/foo/bar" was stored - and read back - as "foo/bar", even
though the reparse point was still flagged as absolute
(SYMLINK_FLAG_RELATIVE cleared).

On a POSIX paths mount the symlink target is stored verbatim, so convert
it directly with cifs_strndup_to_utf16() instead.  This preserves the
leading separator, avoids the leading-backslash stripping that
cifs_convert_path_to_utf16() also performs (a backslash is a valid POSIX
filename character), and uses NO_MAP_UNI_RSVD to match the readback path
in smb2_parse_native_symlink(), which always converts the target with
cifs_strndup_from_utf16() / NO_MAP_UNI_RSVD.  This mirrors how the NFS and
WSL reparse symlink creators convert their targets.

The NT-style absolute symlink handling, which needs the "\??\" prefix and
drive-letter colon preserved, continues to use cifs_convert_path_to_utf16()
together with the existing masking of those bytes.

Fixes: 12b466eb52d9 ("cifs: Fix creating and resolving absolute NT-style symlinks")
Signed-off-by: Steve French <stfrench@microsoft.com>
---
 fs/smb/client/reparse.c | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/fs/smb/client/reparse.c b/fs/smb/client/reparse.c
index cd1e1eaee67a..5cc5b0410d48 100644
--- a/fs/smb/client/reparse.c
+++ b/fs/smb/client/reparse.c
@@ -67,6 +67,7 @@ static int create_native_symlink(const unsigned int xid, struct inode *inode,
 	char *sym = NULL;
 	struct kvec iov;
 	bool directory;
+	int path_len;
 	int rc = 0;
 
 	if (strlen(symname) > REPARSE_SYM_PATH_MAX)
@@ -168,7 +169,21 @@ static int create_native_symlink(const unsigned int xid, struct inode *inode,
 	if (!(sbflags & CIFS_MOUNT_POSIX_PATHS) && symname[0] == '/')
 		sym[0] = sym[1] = sym[2] = sym[5] = '_';
 
-	path = cifs_convert_path_to_utf16(sym, cifs_sb);
+	/*
+	 * On a POSIX paths mount the symlink target is stored verbatim, so
+	 * convert it with cifs_strndup_to_utf16().  cifs_convert_path_to_utf16()
+	 * must not be used here: it strips a leading path separator (it is
+	 * meant for share-relative SMB paths), which would corrupt an absolute
+	 * POSIX symlink target such as "/foo/bar".  Using NO_MAP_UNI_RSVD also
+	 * matches the readback path in smb2_parse_native_symlink().
+	 */
+	if (sbflags & CIFS_MOUNT_POSIX_PATHS)
+		path = cifs_strndup_to_utf16(sym, strlen(sym), &path_len,
+					     cifs_sb->local_nls,
+					     NO_MAP_UNI_RSVD);
+	else
+		path = cifs_convert_path_to_utf16(sym, cifs_sb);
+
 	if (!path) {
 		rc = -ENOMEM;
 		goto out;
-- 
2.53.0

Re: [PATCH v2] smb: client: preserve leading slash for POSIX absolute symlink targets

[Paulo Alcantara]

Steve French <smfrench@gmail.com> writes:

> When creating a native SMB symbolic link (CIFS_SYMLINK_TYPE_NATIVE) whose
> target is an absolute path on a mount that uses POSIX paths, the leading
> path separator was silently dropped from the stored symlink target.
>
> create_native_symlink() converted the target to UTF-16 with
> cifs_convert_path_to_utf16().  That helper is intended for share-relative
> SMB paths and therefore unconditionally strips a leading path separator.
> For an absolute POSIX symlink target the leading '/' is significant, so a
> target of "/foo/bar" was stored - and read back - as "foo/bar", even
> though the reparse point was still flagged as absolute
> (SYMLINK_FLAG_RELATIVE cleared).
>
> On a POSIX paths mount the symlink target is stored verbatim, so convert
> it directly with cifs_strndup_to_utf16() instead.  This preserves the
> leading separator, avoids the leading-backslash stripping that
> cifs_convert_path_to_utf16() also performs (a backslash is a valid POSIX
> filename character), and uses NO_MAP_UNI_RSVD to match the readback path
> in smb2_parse_native_symlink(), which always converts the target with
> cifs_strndup_from_utf16() / NO_MAP_UNI_RSVD.  This mirrors how the NFS and
> WSL reparse symlink creators convert their targets.
>
> The NT-style absolute symlink handling, which needs the "\??\" prefix and
> drive-letter colon preserved, continues to use cifs_convert_path_to_utf16()
> together with the existing masking of those bytes.
>
> Fixes: 12b466eb52d9 ("cifs: Fix creating and resolving absolute NT-style symlinks")
> Signed-off-by: Steve French <stfrench@microsoft.com>
> ---
>  fs/smb/client/reparse.c | 17 ++++++++++++++++-
>  1 file changed, 16 insertions(+), 1 deletion(-)

Reviewed-by: Paulo Alcantara (Red Hat) <pc@manguebit.org>

Re: [PATCH v2] smb: client: preserve leading slash for POSIX absolute symlink targets

[Ralph Boehme]

[-- Attachment #1.1: Type: text/plain, Size: 3269 bytes --]

acked

On 7/5/26 11:17 PM, Steve French wrote:
> When creating a native SMB symbolic link (CIFS_SYMLINK_TYPE_NATIVE) whose
> target is an absolute path on a mount that uses POSIX paths, the leading
> path separator was silently dropped from the stored symlink target.
> 
> create_native_symlink() converted the target to UTF-16 with
> cifs_convert_path_to_utf16().  That helper is intended for share-relative
> SMB paths and therefore unconditionally strips a leading path separator.
> For an absolute POSIX symlink target the leading '/' is significant, so a
> target of "/foo/bar" was stored - and read back - as "foo/bar", even
> though the reparse point was still flagged as absolute
> (SYMLINK_FLAG_RELATIVE cleared).
> 
> On a POSIX paths mount the symlink target is stored verbatim, so convert
> it directly with cifs_strndup_to_utf16() instead.  This preserves the
> leading separator, avoids the leading-backslash stripping that
> cifs_convert_path_to_utf16() also performs (a backslash is a valid POSIX
> filename character), and uses NO_MAP_UNI_RSVD to match the readback path
> in smb2_parse_native_symlink(), which always converts the target with
> cifs_strndup_from_utf16() / NO_MAP_UNI_RSVD.  This mirrors how the NFS and
> WSL reparse symlink creators convert their targets.
> 
> The NT-style absolute symlink handling, which needs the "\??\" prefix and
> drive-letter colon preserved, continues to use cifs_convert_path_to_utf16()
> together with the existing masking of those bytes.
> 
> Fixes: 12b466eb52d9 ("cifs: Fix creating and resolving absolute NT-style symlinks")
> Signed-off-by: Steve French <stfrench@microsoft.com>
> ---
>   fs/smb/client/reparse.c | 17 ++++++++++++++++-
>   1 file changed, 16 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/smb/client/reparse.c b/fs/smb/client/reparse.c
> index cd1e1eaee67a..5cc5b0410d48 100644
> --- a/fs/smb/client/reparse.c
> +++ b/fs/smb/client/reparse.c
> @@ -67,6 +67,7 @@ static int create_native_symlink(const unsigned int xid, struct inode *inode,
>   	char *sym = NULL;
>   	struct kvec iov;
>   	bool directory;
> +	int path_len;
>   	int rc = 0;
>   
>   	if (strlen(symname) > REPARSE_SYM_PATH_MAX)
> @@ -168,7 +169,21 @@ static int create_native_symlink(const unsigned int xid, struct inode *inode,
>   	if (!(sbflags & CIFS_MOUNT_POSIX_PATHS) && symname[0] == '/')
>   		sym[0] = sym[1] = sym[2] = sym[5] = '_';
>   
> -	path = cifs_convert_path_to_utf16(sym, cifs_sb);
> +	/*
> +	 * On a POSIX paths mount the symlink target is stored verbatim, so
> +	 * convert it with cifs_strndup_to_utf16().  cifs_convert_path_to_utf16()
> +	 * must not be used here: it strips a leading path separator (it is
> +	 * meant for share-relative SMB paths), which would corrupt an absolute
> +	 * POSIX symlink target such as "/foo/bar".  Using NO_MAP_UNI_RSVD also
> +	 * matches the readback path in smb2_parse_native_symlink().
> +	 */
> +	if (sbflags & CIFS_MOUNT_POSIX_PATHS)
> +		path = cifs_strndup_to_utf16(sym, strlen(sym), &path_len,
> +					     cifs_sb->local_nls,
> +					     NO_MAP_UNI_RSVD);
> +	else
> +		path = cifs_convert_path_to_utf16(sym, cifs_sb);
> +
>   	if (!path) {
>   		rc = -ENOMEM;
>   		goto out;


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