[release/2.2] Fix unintended dropping of mount flags for read-only bind-mounts in user namespaces#12944
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mxpv merged 2 commits intocontainerd:release/2.2from Feb 27, 2026
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…ead of values The loop `for flag := range unprivilegedFlags` iterates over slice indices (0,1,2,3,4,5,6) rather than the actual flag values (MS_RDONLY, MS_NODEV, etc). This was a porting error from moby/moby where the data structure was a map (where `for k := range m` yields keys/values). As a result, MS_NOEXEC, MS_NOATIME, MS_RELATIME, and MS_NODIRATIME are never detected or preserved. In user namespaces, this causes bind-mount remounts to fail with EPERM when any of these flags are locked on the parent mount, because the kernel requires all CL_UNPRIVILEGED locked flags to be preserved during remount. MS_RDONLY (0x1), MS_NOSUID (0x2), and MS_NODEV (0x4) happened to work by coincidence because their values equal low index numbers. Fix by using `for _, flag := range` to iterate over values. Signed-off-by: Luke Hinds <[email protected]>
Mounts a tmpfs with MS_NOEXEC, MS_NOATIME, and MS_NODIRATIME and verifies that getUnprivilegedMountFlags detects all of them. These three flags were the ones missed by the range-over-indices bug. Also verifies that flags not present on the mount (MS_NOSUID, MS_NODEV, MS_RDONLY) are not falsely reported. Signed-off-by: Luke Hinds <[email protected]>
dcantah
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mxpv
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This is an automated cherry-pick of #12941
/assign AkihiroSuda