[LU-13985] seq_file next function must change *pos

• Type: Bug
• Resolution: Fixed
• Priority: Minor
• Fix Version/s: Lustre 2.14.0
• Severity: 3
• Assignee: Neil Brown
• Reporter: Neil Brown

Description

If the .next function used to implement a seq_file ever doesn't change the value of *pos, the result of reading the file can be incorrect.

This specifically includes when the end-of-file is found and NULL is returned.

The error occurs if a 'read()' request is performed while the file pointer is in the middle of the last record, as you could happen if you seek there, or read a block that is not a whole number of records.  In this case the remainder of the last record will be returned followed by a complete copy of that last record.  To avoid the complete copy, *pos must be be changed so that a subsequent call to ->start reports an immediate end of file.
Because this is a common bug, seq_file core code will report a warning if *pos is not changed.

There are several ->next functions in lustre which don't always change *pos.

 

Issue Links

• duplicates: LU-13543 hsm.actions file is broken on RHEL 8.2
• is related to: LU-8066 Move lustre procfs handling to sysfs and debugfs.

Comments

[Peter Jones]

Landed for 2.14

[Gerrit Updater]

Oleg Drokin ([e-mail]) merged in patch https://review.whamcloud.com/40035/
Subject: LU-13985 lustre: seq_file .next functions must update *pos
Project: fs/lustre-release
Branch: master
Current Patch Set:
Commit: 817d6c116599639599919bcde7999a7f06b74d2c

[Gerrit Updater]

Neil Brown ([e-mail]) uploaded a new patch: https://review.whamcloud.com/40035
Subject: LU-13985 lustre: seq_file .next functions must update *pos
Project: fs/lustre-release
Branch: master
Current Patch Set: 1
Commit: 10f498a9e008cf31fa8b45b04b31bf361e5909ab