** Also affects: linux (Ubuntu Eoan)
Importance: Undecided
Status: New
** Also affects: linux (Ubuntu Focal)
Importance: Undecided
Status: New
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https://bugs.launchpad.net/bugs/1872757
Title:
shiftfs: O_TMPFILE reports ESTALE
Status in linux package in Ubuntu:
In Progress
Status in linux source package in Eoan:
New
Status in linux source package in Focal:
New
Bug description:
SRU Justification
Impact: Christian Kellner reported that creating temporary files via
O_TMPFILE shiftfs reports ESTALE. This can be reproduced via:
import tempfile
import os
def test():
with tempfile.TemporaryFile() as fd:
fd.write("data".encode('utf-8'))
# re-open the file to get a read-only file descriptor
return open(f"/proc/self/fd/{fd.fileno()}", "r")
def main():
fd = test()
fd.close()
if __name__ == "__main__":
main()
a similar issue was reported here:
https://github.com/systemd/systemd/issues/14861
Fix: Our revalidate methods were very opinionated about whether or not
a dentry was valid when we really should've just let the underlay tell
us what's what. This has led to bugs where a ESTALE was returned for
e.g. temporary files that were created and directly re-opened
afterwards through /proc/<pid>/fd/<nr-of-deleted-file>. When a file is
re-opened through /proc/<pid>/fd/<nr> LOOKUP_JUMP is set and the vfs
will revalidate via d_weak_revalidate(). Since the file has been
unhashed or even already gone negative we'd fail the open when we
should've succeeded.
I had also foolishly provided a .tmpfile method which so far only has
caused us trouble. If we really need this then we can reimplement it
properly but I doubt it. Remove it for now.
Regression Potential: Limited to shiftfs.
Test Case: Build a kernel with fix applied and run above reproducer.
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