From: Pali Rohár pali@kernel.org
[ Upstream commit a3e771afbb3bce91c8296828304903e7348003fe ]
For TRANS2 QUERY_PATH_INFO request when the path does not exist, the Windows NT SMB server returns error response STATUS_OBJECT_NAME_NOT_FOUND or ERRDOS/ERRbadfile without the SMBFLG_RESPONSE flag set. Similarly it returns STATUS_DELETE_PENDING when the file is being deleted. And looks like that any error response from TRANS2 QUERY_PATH_INFO does not have SMBFLG_RESPONSE flag set.
So relax check in check_smb_hdr() for detecting if the packet is response for this special case.
This change fixes stat() operation against Windows NT SMB servers and also all operations which depends on -ENOENT result from stat like creat() or mkdir().
Signed-off-by: Pali Rohár pali@kernel.org Signed-off-by: Steve French stfrench@microsoft.com Signed-off-by: Sasha Levin sashal@kernel.org ---
**YES** This commit should be backported to stable kernel trees. Here's my extensive analysis: ## Backport Recommendation: YES ### Nature of the Fix This is a **targeted bug fix** that addresses a specific protocol compliance issue with Windows NT SMB servers. The commit fixes a fundamental problem where basic file operations (`stat()`, `creat()`, `mkdir()`) fail against Windows NT servers due to overly strict SMB header validation. ### Code Change Analysis The fix is remarkably **simple and contained** - only 8 lines of code in a single function: ```c /bin /bin.usr-is-merged /boot /dev /etc /home /init /lib /lib.usr- is-merged /lib64 /lost+found /media /mnt /opt /proc /root /run /sbin /sbin.usr-is-merged /snap /srv /sys /tmp /usr /var * Windows NT server returns error resposne (e.g. STATUS_DELETE_PENDING * or STATUS_OBJECT_NAME_NOT_FOUND or ERRDOS/ERRbadfile or any other) * for some TRANS2 requests without the RESPONSE flag set in header. */ if (smb->Command == SMB_COM_TRANSACTION2 && smb->Status.CifsError != 0) return 0; ``` The change is in the `check_smb_hdr()` function in `fs/smb/client/misc.c`, which validates SMB packet headers. The fix **relaxes validation** only for a very specific case: TRANS2 commands returning errors from Windows NT servers. ### Risk Assessment: LOW 1. **Surgical precision**: Only affects SMB1 TRANS2 error responses, leaving normal operation paths untouched 2. **Conservative approach**: The condition `smb->Status.CifsError != 0` ensures this only applies to actual error responses 3. **No behavioral changes** for compliant servers that properly set the RESPONSE flag 4. **Well-established code path**: The `check_smb_hdr()` function is mature and stable ### Impact Assessment: HIGH 1. **Fixes broken functionality**: Without this fix, basic file operations fail completely against Windows NT servers 2. **Backward compatibility**: Restores support for legacy but still-used server environments 3. **User-visible improvement**: Directly fixes `stat()`, `creat()`, and `mkdir()` operations 4. **No regressions**: Modern SMB servers continue to work as before ### Comparison with Similar Commits Looking at the provided similar commits: - **Similar Commit #2** (Status: YES): Also adds new status code mappings for better server compatibility - **Similar Commit #3** (Status: YES): Reduces unnecessary network roundtrips by improving error handling - **Similar Commit #4** (Status: YES): Fixes WSL reparse point querying over SMB1 - **Similar Commit #5** (Status: YES): Fixes missing resource cleanup This commit follows the **same pattern** as these approved backports: small, targeted fixes that improve compatibility and fix real-world issues without introducing new features or architectural changes. ### Technical Justification The Windows NT server behavior described in the commit is **non-compliant but real**: these servers return error responses for TRANS2 QUERY_PATH_INFO requests without setting the `SMBFLG_RESPONSE` flag. The current strict validation incorrectly treats these as invalid packets, causing the CIFS client to fail when it should handle the errors properly. The fix is **protocol-aware** and **conservative** - it only relaxes validation for the specific case where we know Windows NT behaves differently, ensuring no impact on standard-compliant servers. ### Stable Tree Suitability This commit perfectly fits stable tree criteria: - ✅ **Important bug fix** affecting real-world usage - ✅ **Minimal and contained** change with clear scope - ✅ **No new features** - purely fixes existing broken functionality - ✅ **Low regression risk** due to targeted nature - ✅ **Production-ready** code following established patterns This should be backported to all stable kernels that support SMB1 client functionality, as it fixes a fundamental compatibility issue without any meaningful risk of regression.
fs/smb/client/misc.c | 8 ++++++++ 1 file changed, 8 insertions(+)
diff --git a/fs/smb/client/misc.c b/fs/smb/client/misc.c index 4373dd64b66d4..5122f3895dfc2 100644 --- a/fs/smb/client/misc.c +++ b/fs/smb/client/misc.c @@ -323,6 +323,14 @@ check_smb_hdr(struct smb_hdr *smb) if (smb->Command == SMB_COM_LOCKING_ANDX) return 0;
+ /* + * Windows NT server returns error resposne (e.g. STATUS_DELETE_PENDING + * or STATUS_OBJECT_NAME_NOT_FOUND or ERRDOS/ERRbadfile or any other) + * for some TRANS2 requests without the RESPONSE flag set in header. + */ + if (smb->Command == SMB_COM_TRANSACTION2 && smb->Status.CifsError != 0) + return 0; + cifs_dbg(VFS, "Server sent request, not response. mid=%u\n", get_mid(smb)); return 1;