core/mount: fix getUnprivilegedMountFlags iterating over indices instead of values#12939
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lukefr09 wants to merge 2 commits intocontainerd:mainfrom
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core/mount: fix getUnprivilegedMountFlags iterating over indices instead of values#12939lukefr09 wants to merge 2 commits intocontainerd:mainfrom
lukefr09 wants to merge 2 commits intocontainerd:mainfrom
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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
approved these changes
Feb 26, 2026
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Summary
getUnprivilegedMountFlagsusesfor flag := range unprivilegedFlagswhich iterates over slice indices (0–6) instead of the actual flag values (MS_RDONLY,MS_NODEV, etc.)map[uint64]string(wherefor k := range myields keys). When converted to[]int, the loop was not updated tofor _, flag := range.MS_NOEXEC,MS_NOATIME,MS_RELATIME, andMS_NODIRATIMEare never detected or preserved during bind-mount remounts in user namespacesMS_RDONLY(0x1),MS_NOSUID(0x2), andMS_NODEV(0x4) work by coincidence because their values equal low slice indicesEPERMwhen any of the missed flags are locked on the parent mountFix
Change
for flag := rangetofor _, flag := rangeto iterate over values.Test plan
rooption succeed in user namespace environments whereMS_NOEXEC,MS_NOATIME,MS_RELATIME, orMS_NODIRATIMEare locked on the parent mountnoexecornoatime