This bug also affects the 3.13 kernel in Ubuntu Trusty.
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https://bugs.launchpad.net/bugs/1479468
Title:
OverlayFS: Wrong mnt_id and path reported in /proc
Status in linux package in Ubuntu:
Triaged
Status in linux source package in Vivid:
Fix Released
Bug description:
SRU Justification:
[Impact]
I am running Ubuntu Vivid (3.19.0-22-generic #22-Ubuntu SMP Tue Jun 16
17:15:15 UTC 2015 x86_64 x86_64 x86_64 GNU/Linux). There are two
issues in OverlayFS as follows:
1. /proc/<pid>/fdinfo/<fd> reports wrong mnt_id (non-existent in
/proc/<pid>/mountinfo)
2. /proc/<pid>/fd/<fd> shows incorrect path for the symlink target
[Fix]
These problems can be easily reproduced with the shell script below.
Fortunately, both problems have been fixed in the upstream's master
branch of the kernel via the following commits:
torvalds 4.0: 155e35d4d VFS: Introduce inode-getting helpers for
layered/unioned fs environments (this is already in ubuntu-vivid)
torvalds 4.0: df1a085af VFS: Add a fallthrough flag for marking virtual
dentries
torvalds 4.2-rc2: f25801ee4 overlay: Call ovl_drop_write() earlier in
ovl_dentry_open()
torvalds 4.2-rc2: 4bacc9c92 overlayfs: Make f_path always point to the
overlay and f_inode to the underlay
torvalds 4.2-rc2: 9391dd00d fix a braino in ovl_d_select_inode()
(The commit df1a085af may technically not be needed but it prevents a
conflict when applying 4bacc9c92.)
[Test Case]
Simple script to reproduce the problem:
#!/bin/bash
set -eu
ERROR=0
setup() {
setup_mount
start_python > /dev/null 2>&1 &
BASH_PID=$!
PYTHON_PID=$(ps -C python | awk '/python/ { print $1 }')
sleep 1
}
setup_mount() {
mkdir overlay_test
cd overlay_test
mkdir a b c z
sudo mount -t overlay -o lowerdir=a,upperdir=b,workdir=c overlayfs z
}
start_python() {
python << EOF
import time
fd = open("z/file", "w")
time.sleep(10)
EOF
}
check_path() {
WD=$(pwd)
if ! ls -l /proc/$PYTHON_PID/fd | grep -qw "$WD/z/file"; then
ERROR=1
echo "ERROR! expected $WD/z/file"
set -x
ls -l /proc/$PYTHON_PID/fd
set +x
fi
}
check_mnt_id() {
FDINFO_MNT_ID=$(awk '/mnt_id:/ { print $2 }' /proc/$PYTHON_PID/fdinfo/3)
MOUNTINFO_MNT_ID=$(awk '/overlayfs/ { print $1 }' /proc/self/mountinfo)
if [[ $FDINFO_MNT_ID -ne $MOUNTINFO_MNT_ID ]]; then
ERROR=1
echo "ERROR! mnt_id $FDINFO_MNT_ID not in /proc/self/mountinfo"
set -x
cat /proc/$PYTHON_PID/fdinfo/3
cat /proc/self/mountinfo
set +x
fi
}
finish() {
kill -INT $PYTHON_PID > /dev/null 2>&1
sudo umount z
cd $ORIG_WD
rm -rf overlay_test
}
main() {
ORIG_WD=$(pwd)
setup
check_path
check_mnt_id
finish
[[ $ERROR -eq 0 ]] && echo "OverlayFS looks good."
}
main
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