On Fri, 1 Dec 2023, Jozef Riha wrote: > Hello list, > > we've recently came across an interesting problem on one of our AIX > systems which we were unable to reproduce on Linux host but we > discovered that FreeBSD (11) is showing the same behaviour. > > Preparation: > - on AIX/FreeBSD system inside /tmp with the standard 1777 > permissions create an empty file > touch foofile > chmod 600 foofile > chown root:system foofile > > To reproduce: > - in WinSCP login as a regular (non-root) user, browse to /tmp > - navigate to /tmp/foofile, bring up a context menu (right-click), > select Rename (F2) > - receive a pop-up "Permission denied", click Abort > - refresh directory listing > - notice a new barfile (hardlink to foofile) > > Expectation: > - hardlink should not be present (rename is supposed to be atomic > hence either it is processed fully or not at all). > > It all comes down to a different behaviour of ln (link) on different systems: > # AIX/FreeBSD, regular user inside /tmp > ln foofile barfile # rc=0; link is created > > # Linux > ln foofile barfile # rc=1 (error: Operation not permitted); link is not created > > Due to the directory having sticky bit on, the operation of renaming > for AIX/FreeBSD fails in the very last stage (unlink), leaving a file > behind. > > As a workaround posix-rename (which is not race-free) could be used > but there seems to be a limited support among GUI clients (for WinSCP > there is a ticket opened to add this feature: > https://winscp.net/tracker/2231). > > Is there a way to address this problem in OpenSSH code-base? I doubt it - sftp-server already tries to clean up when a legacy rename operation fails. See the logic starting here: https://github.com/openssh/openssh-portable/blob/V_9_5_P1/sftp-server.c#L1285 If file permissions are preventing this then there isn't anything more it can do AFAIK. The SSH2_FXP_RENAME operation was just badly specified in the sftp protocol, which is why we added posix-rename. -d _______________________________________________ openssh-unix-dev mailing list openssh-unix-dev@xxxxxxxxxxx https://lists.mindrot.org/mailman/listinfo/openssh-unix-dev
