Bug 201971

Summary: wrong status_to_posix_error mapping
Product: File System Reporter: omgbebebe
Component: CIFSAssignee: fs_cifs (fs_cifs)
Status: NEW ---    
Severity: normal CC: gkot
Priority: P1    
Hardware: All   
OS: Linux   
Kernel Version: 4.19.7 Tree: Mainline
Regression: No
Attachments: example code to test shared locks

Description omgbebebe 2018-12-12 08:58:46 UTC
Created attachment 279959 [details]
example code to test shared locks

While resolving a bug with locks on samba shares we found a strange behavior. When a file locked by one node and we trying to lock it from another node it fail with errno 5 (EIO) but in that case errno must be set to (EACCES | EAGAIN). This isn't happening when we try to lock file second time on same node. In this case it returns EACCES as expected. Also this issue not reproduces when we use SMB1 protocol (vers=1.0 in mount options).

Further investigation showed that the mapping from status_to_posix_error is different for SMB1 and SMB2+ implementations. For SMB1 mapping is [NT_STATUS_LOCK_NOT_GRANTED to ERRlock](https://github.com/torvalds/linux/blob/master/fs/cifs/netmisc.c#L322) to [-EACCES](https://github.com/torvalds/linux/blob/master/fs/cifs/netmisc.c#L66)
but for SMB2+ mapping is [STATUS_LOCK_NOT_GRANTED to -EIO](https://github.com/torvalds/linux/blob/master/fs/cifs/smb2maperror.c#L383)

Quick changes in SMB2+ mapping from EIO to EACCES has fixed our issue.

Is it bug in mappings in SMB2/3 implementation or it is a new behaviour that we should take in account in future?

PS. I attached example code to test shared locks. To reproduce our case it should be executed on same shared file twice.

Expected behavior:

nodeA $ ./share_lock /mnt/server_public/file_samba
File locked successfully.
Press any key to exit...

# in another console
nodeA $ ./share_lock /mnt/server_public/file_samba
fcntl error: 13, Permission denied

Wrong behavior:

nodeA $ ./share_lock /mnt/server_public/file_samba
File locked successfully.
Press any key to exit...

# on second node
nodeB $ ./share_lock /mnt/server_public/file_samba
fcntl error: 5, Input/output error